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Introduction

The early evolution of the archosauromorphs during the Triassic is an excellent example of an adaptative radiation in the fossil record (Brusatte et al., 2008; Nesbitt, 2011). In the aftermath of the Permo-Triassic mass extinction, multiple, anatomically well diversified archosauromorph groups appear for the first time in the fossil record, including semi aquatic or entirely aquatic forms (e.g., tanystropheids, doswelliids, proterochampsids, some poposauroids), highly specialized herbivores (e.g., allokotosaurians, rhynchosaurs), and massive predators (e.g., erythrosuchids, “rauisuchians”). As a result, the early evolution of archosauromorphs constitutes an excellent empirical case study to shed light on evolutionary radiations in deep time and the timing and processes of recovery of terrestrial faunas after a mass extinction. However, macroevolutionary studies of early archosauromorphs are substantially limited by poor knowledge of their phylogenetic relationships (Ezcurra, Butler & Gower, 2013). Many early archosauromorph species have not been previously included in a quantitative phylogenetic analysis, and have been historically included within groups that are probably non-monophyletic as often conceived (e.g., “Prolacertiformes,” Proterosuchidae; Dilkes, 1998; Modesto & Sues, 2004; Gottmann-Quesada & Sander, 2009; Ezcurra, Lecuona & Martinelli, 2010; Ezcurra, Butler & Gower, 2013; Ezcurra, Scheyer & Butler, 2014). In addition, the higher-level phylogenetic relationships of the main lineages of archosauromorphs are highly contentious and there is limited consensus between the results recovered by different studies (e.g., Dilkes, 1998; Modesto & Sues, 2004; Gottmann-Quesada & Sander, 2009; Ezcurra, Scheyer & Butler, 2014; Pritchard et al., 2015).

One of the main early archosauromorph groups that need an exhaustive phylogenetic study is “Proterosuchia,” which, as historically conceived, includes members of both Proterosuchidae and Erythrosuchidae (Reig, 1970; Charig & Reig, 1970; Charig & Sues, 1976; Ezcurra, Butler & Gower, 2013). Indeed, most proterosuchian species have not yet been included in quantitative phylogenetic analyses, and their phylogenetic positions among basal archosauriforms or within either Proterosuchidae or Erythrosuchidae is in state of flux (e.g., Guchengosuchus shiguaiensis, Cuyosuchus rusconi, Chalishevia cothurnata, Shansisuchus kuyeheensis, Garjainia madiba, “Chasmatosaurusyuani, “Blomosuchus georgii,” Vonhuenia friedrichi, Chasmatosuchus rossicus, Tasmaniosaurus triassicus, Kalisuchus rewanensis). The proterosuchians represent the most basal known archosauriforms, and, as a result, an understanding of their phylogenetic relationships is crucial to attempts to reconstruct the interrelationships of more crownward archosauriforms and the early evolutionary history of Archosauriformes as a whole. However, the poor current phylogenetic understanding of the proterosuchians hampers the development of diagnoses for Proterosuchidae and Erythrosuchidae, and the taxonomic inclusiveness of these clades remains uncertain (Ezcurra, Butler & Gower, 2013). This contribution focuses on the phylogenetic relationships of non-archosaurian archosauromorphs, with a special emphasis on the interrelationships among taxa historically identified as proterosuchian archosauriforms.

Previous work

In the following pages I discuss the work conducted by previous authors on the higher-level phylogenetic relationships of Archosauromorpha, with emphasis in the historical background of the phylogenetic interrelationships of the “Proterosuchia.” The cladistic history of the relationships among non-proterosuchian archosauriforms has been recently discussed by Nesbitt (2011) and, as a result, is not summarized here.

The higher-level phylogenetic relationships of early archosauromorphs

During the pre-cladistic era, small and gracile Permo-Triassic diapsids (including some early archosauromorphs) were frequently included within the Order “Eosuchia,” which was suggested to have given rise to lepidosauromorphs, archosaurs and even some marine reptiles, such as plesiosaurs (e.g., Romer, 1956; Romer, 1966; Benton, 1982). However, the classification of diapsid reptiles was chaotic and in state of flux prior to the advent of quantitative cladistic analyses. The first cladistic analyses that focused on the higher-level relationships of archosauromorphs were conducted by Benton (1984a), Benton (1985) and Evans (1984). Benton (1984a) and Benton (1985) recovered four main clades within Archosauromorpha, namely Pterosauria, Rhynchosauria, “Prolacertiformes” and Archosauria (Fig. 1A). Pterosauria represented the earliest branching archosauromorphs, and Trilophosaurus and Rhynchosauria were successive sister-taxa of a clade composed of “Prolacertiformes” and Archosauria (Benton, 1985). “Prolacertiformes” included Permo-Triassic long-necked archosauromorphs (e.g., Protorosaurus, Prolacerta and tanystropheids), and archosaurs included more bulky forms, such as Erythrosuchus, Euparkeria, and dinosaur and crocodile precursors (thus being largely equivalent to the current concept of Archosauriformes). In particular, Benton (1985) was uncertain whether the South African archosauromorph Proterosuchus represented a prolacertiform or an archosaur. The analysis of Evans (1984) and subsequent analyses (e.g., Gauthier, Kluge & Rowe, 1988; Chatterjee, 1986; Bennett, 1996) also placed Rhynchosauria as the sister-taxon of a clade composed of “Prolacertiformes”/“Protorosauria” and Archosauria (Figs. 1C1E). In addition, Evans (1988), Evans (1990) and Gauthier, Kluge & Rowe (1988) tentatively added other main lineages to Archosauromorpha, namely the aquatic choristoderans and thalattosaurians, and the gliding kuehneosaurids (Figs. 1B and 1D). As a result, the pioneering cladistic analyses conducted during the 1980s largely agreed in the recognition of three clades of archosauromorphs (i.e., “Prolacertiformes,” Rhynchosauria, and Archosauriformes) and the basal position of rhynchosaurs with respect to prolacertiforms and archosauriforms, a result also recovered by some analyses during the subsequent decade (e.g., Bennett, 1996). However, a point of disagreement between these early analyses was the position of Trilophosaurus, being alternatively placed as the most basal archosauromorph to the exclusion of pterosaurs (Benton, 1985), as the sister-taxon of Rhynchosauria (Chatterjee, 1986), or as the sister-taxon of “Prolacertiformes” + Archosauriformes (Evans, 1988).

Figure 1: Phylogenetic trees depicting selected previous hypotheses for the higher-level relationships of early archosauromorphs in the period 1985–1996.

(A) Benton (1985); (B) Evans (1988); (C) Chatterjee (1986); (D) Gauthier, Kluge & Rowe (1988); and (E) Bennett (1996). Abbreviations: Ar., Archosauromorpha; Ara, Araeoscelidia; Arc., Archosauriformes; Arco., Archosauria; Di., Diapsida; Neo., Neodiapsida; Pr., Prolacertiformes; Sa., Sauria.

Gauthier (1994) recovered a monophyletic “Prolacertiformes” as the earliest branch of Archosauromorpha, whereas rhynchosaurs were the sister-taxon of Trilophosaurus and Archosauriformes, contrasting with previous analyses. Dilkes (1998), Sues (2003) and Modesto & Sues (2004) (the latter two analyses used a modified version of the data matrix of Dilkes (1998)) recovered the South African Prolacerta as more closely related to Archosauriformes than to any other archosauromorph, thus resulting in a polyphyletic “Prolacertiformes” (Fig. 2A). These authors found a monophyletic “Protorosauria” (formed by Protorosaurus, tanystropheids and drepanosaurs) as the earliest branching archosauromorphs and Trilophosaurus (together with Teraterpeton in the case of Sues et al. (2003)) as the sister-taxon of the clade composed of Rhynchosauria, Prolacerta and Archosauriformes. In addition, Dilkes (1998) and Gottmann-Quesada & Sander (2009) recovered the enigmatic choristoderan diapsids outside Sauria (i.e., Lepidosauromorpha and Archosauromorpha) (Fig. 2C), as also suggested by Evans & Hecht (1993).

Figure 2: Phylogenetic trees depicting selected previous hypotheses for the higher-level relationships of early archosauromorphs in the period 1998–2009.

(A) Dilkes (1998); (B) Müller (2004); and (C) Gottmann-Quesada & Sander (2009). Abbreviations: Ar., Archosauromorpha; Arc., Archosauriformes; Ch., Choristodera; Dr., Drepanosauridae; Rhy., Rhynchosauria; Rhyn., Rhynchosauridae; Sa., Sauria; Ta., Tanystropheidae.

Müller (2004) and Bickelmann, Müller & Reisz (2009) also recovered a non-monophyletic “Prolacertiformes,” in which Tanystropheus, Macrocnemus and Prolacerta were successive sister-taxa of a trichotomy composed of Trilophosaurus, Rhynchosauria and Archosauriformes (Fig. 2B). In these analyses, choristoderans were recovered as the earliest branching members of Lepidosauromorpha. Borsuk-Białynicka & Evans (2009) found results consistent with those of Dilkes (1998) and Müller (2004), respectively, based on slightly modified versions of those data matrixes. Gottmann-Quesada & Sander (2009) found Trilophosaurus as the sister-taxon of Rhynchosauria and “Protorosauria” as a paraphyletic group, with a clade composed of Protorosaurus and the drepanosaur Megalancosaurus found as the sister-taxon of tanystropheids and more crownward archosauromorphs. Gottmann-Quesada & Sander (2009) also found Prolacerta as the sister-taxon of Archosauriformes.

Ezcurra, Scheyer & Butler (2014) found a result largely consistent with that of Dilkes (1998), but noted that since the main purpose of their analysis was not to reconstruct the higher-level relationships of archosauromorphs, the recovery of a monophyletic “Protorosauria” was potentially an artefact of incomplete taxon and character sampling, and that Aenigmastropheus and Protorosaurus might in reality be more basal than tanystropheids (Fig. 3B). Pritchard et al. (2015) conducted a phylogenetic analysis that found a topology that clearly contrasts with those of the preceding 10 years. In this analysis, “Prolacertiformes” and “Protorosauria” were recovered as non-monophyletic groups, with Protorosaurus as the earliest branching archosauromorph and Prolacerta the sister-taxon of Archosauriformes (Fig. 3A). Pritchard et al. (2015) found rhynchosaurs, tanystropheids and a clade composed of Trilophosaurus spp. and Teraterpeton as successive sister-taxa of Prolacerta + Archosauriformes. Nesbitt et al. (2015) conducted another analysis based on a modified version of the data matrix of Pritchard et al. (2015), and found tanystropheids, rhynchosaurs, and allokotosaurians (a new group of archosauromorphs formed by Azendohsaurus, Trilophosaurus, and their kin) as successive sister-taxa of Prolacerta + Archosauriformes (Fig. 3C), thus being more consistent with previous analyses that repeatedly recovered tanystropheids as more basal than rhynchosaurs and crownward archosauromorphs (e.g., Gauthier, 1994; Dilkes, 1998; Müller, 2004; Gottmann-Quesada & Sander, 2009; Ezcurra, Scheyer & Butler, 2014).

Figure 3: Phylogenetic trees depicting selected previous hypotheses for the higher-level relationships of early archosauromorphs in the period 2014–2015.

(A) Pritchard et al. (2015); (B) Ezcurra, Scheyer & Butler (2014); and (C) Nesbitt et al. (2015). Abbreviations: All., Allokotosauria; Ar., Archosauromorpha; Ara, Araeoscelidia; Arc., Archosauriformes; Arco., Archosauria; Di., Diapsida; Lep., Lepidosauromorpha; Neo., Neodiapsida; Pro., Proterosuchidae; Prot., Protorosauria; Proto., Protorosauridae; Rh., Rhynchocephalia; Rhy., Rhynchosauria; Sa., Sauria; Saur., Sauropsida; Ta., Tanystropheidae; Young., Younginiformes.

Cladistic analyses focused on the higher-level phylogenetic relationships of Archosauromorpha have found rather disparate results over the last 30 years, but, in the last decade, most analyses have agreed on the polyphyletic nature of “Prolacertiformes” as traditionally conceived and the placement of protorosaurs/tanystropheids as the sister-taxon of rhynchosaurs, Prolacerta, and archosauriforms. However, there is still a substantial lack of consensus as to the monophyly and taxonomic content of “Protorosauria” and the position of allokotosaurians also represents a topic to be explored in the coming years.

Figure 4: Chronostratigraphic diagram of proterosuchian-bearing units (sensu Ezcurra, Butler & Gower, 2013; Ezcurra et al., 2015).

Ages of South African units based on Rubidge (2005) and Rubidge et al. (2013); Russian units based on Newell et al. (2010) and Newell et al. (2012); Chinese and Indian units based on Lucas (2010) and Liu, Li & Li (2013); South American units based on Piñeiro et al. (2003) and Spalletti, Fanning & Rapela (2008); and Australian units based on Ezcurra (2014) and Warren & Hutchinson (1990). Asterisks indicate radioistopically dated boundaries. It should be noted that the lower Ermaying and Heshanggou formations of China, and the South American, Indian and Australian units belong to different basins, respectively. Russian Gorizonts (=Horizonts) include several formations and basins. Abbreviations: Ans, Anisian; AZ, Assemblage Zone; Chx, Changhsingian; Crn, Carnian; Fm, Formation; G, Gorizont; Ind, Induan; Lad, Ladinian; Nor, Norian; Ole, Olenekian; Ryb, Rybinskian; Slu, Sludkian; Sub, Subzone; Supergo, Supergorizont; Ust, Ustmylian; Vok, Vokhmian; Wuc, Wuchiapingian. Geological timescale after Gradstein et al. (2012).

Historical background of the phylogenetic relationships of “Proterosuchia”

The first discovered proterosuchian fossil was collected in the Lower Triassic Panchet Formation of India (Fig. 4) and described by Huxley (1865) as a new genus and species “Ankistrodon indicus.” This species is based on a fragment of tooth-bearing bone interpreted by Huxley (1865: 12) as a “thecodont saurian” with a tooth morphology closely resembling that of other carnivorous “thecodonts” and dinosaurs. During the early 20th century, Broom (1903a) described the remains of a fossil reptile collected in the Lower Triassic part of the Karoo Basin of Eastern Cape Province, South Africa, and erected the new species Proterosuchus fergusi. He stated that Proterosuchus differed so greatly from any hitherto described species that it was difficult to decide its affinities (Broom, 1903a: 162). However, mainly based on the morphology of the palatal teeth, Broom (1903a: 163) concluded that Proterosuchus was a primitive “Rhynchocephalian” (conceived by Broom as a group of primitive reptiles including the extant Sphenodon and taxa like the extinct Procolophon and Protorosaurus) that showed “a considerable degree of specialisation along the line which gave rise to the early Crocodiles and Dinosaurs.” Two years later, the same author named Erythrosuchus africanus from the early Middle Triassic of South Africa and assigned it to the Phytosauria (Broom, 1905). Subsequently, Broom (1906) reviewed the classification of “Diaptosauria” (a group that included several amniote clades, such as protorosaurs, pelycosaurs, rhynchosaurs, procolophonids, choristoderans and rhynchocephalians; sensu Osborn, 1903) and coined the new suborder or order “Proterosuchia,” within which he included Proterosuchus. Broom (1906) interpreted the “Proterosuchia” as more closely related to the Rhynchocephalia than to other Triassic diaptosaurian orders, such as Phytosauria and “Gnathodontia” (e.g., Howesia).

Huene (1908) considered “Proterosuchia” as a family-ranked group, resulting in the new taxon Proterosuchidae. Subsequently, Huene (1908) described a new and more complete specimen of Erythrosuchus and proposed the new order “Pelycosimia,” in which he included Erythrosuchus and the derived rhynchosaur “Scaphonyx” (=Hyperodapedon sensu Langer et al., 2000), among other taxa (Huene, 1911). Huene (1911) interpreted the “Pelycosimia” as closely related to pelycosaurian synapsids. However, Watson (1917) recognized Erythrosuchus as a member of the “Thecodontia” and coined the monospecific, family-ranked clade Erythrosuchidae. Subsequently, Huene (1920) agreed with this new interpretation and included the “Pelycosimia” within the order “Thecodontia” as a suborder.

Haughton (1924) described the new species “Chasmatosaurus vanhoepeni” from the same horizon as Proterosuchus fergusi, and assigned it to its own family, Chasmatosauridae. Willistons (1925) considered the Proterosuchia as a non-thecodont order of diapsids. Subsequently, the suborder Erythrosuchia was erected by Goodrich (1930) in order to include only Erythrosuchus. Kuhn (1933) considered Proterosuchus to be closely related to the probable stem-crocodylomorphs Dyoplax and Erpetosuchus, whereas he interpreted Erythrosuchus and “Chasmatosaurus” as forming a group of closely related taxa together with the aetosaur “Acompsosaurus.” Broili & Schröder (1934) also considered “Chasmatosaurus” and Erythrosuchus to be closely related.

Between the 1940s and 1960s several classifications were proposed that mostly agreed in considering proterosuchids and erythrosuchids as closely related taxa forming a single group (“Proterosuchia” or Proterosuchoidea, depending on the rank employed by each author) within a primitive stock of thecodonts (e.g., Romer, 1945; Romer, 1956; Huene, 1948; Huene, 1956; Hoffstetter, 1955; Kuhn, 1961; Reig, 1961). Ochev (1958) described Garjainia prima from the late Early Triassic of Russia and included it in its own family, Garjainiidae. Similarly, Huene (1960) described “Vjushkoviatriplicostata from the same horizon as Garjainia prima and erected the new family Vjushkoviidae, and Young (1964) described Shansisuchus shansisuchus from the Middle Triassic of China and coined the family Shansisuchidae. These families were included within the “Proterosuchia,” together with Proterosuchidae and Erythrosuchidae, by some authors (e.g., Young, 1964; Reig, 1961; Kuhn, 1966). Tatarinov (1961) proposed that “Vjushkovia”, Garjainia, “Dongusia,” and Cuyosuchus were subjective junior synonyms of Erythrosuchus, a hypothesis that was followed by several other authors (e.g., Hughes, 1963; Ewer, 1965; Romer, 1966; Romer, 1972a; Cruickshank, 1972), but rejected by Young (1964),Charig & Reig (1970), and subsequent workers (e.g., Parrish, 1992; Sennikov, 1995a; Sennikov, 1995b; Gower & Sennikov, 1996; Gower & Sennikov, 1997; Gower & Sennikov, 2000; Desojo, Arcucci & Marsicano, 2002; Ezcurra, Lecuona & Martinelli, 2010; Ezcurra, Butler & Gower, 2013; Ezcurra, Scheyer & Butler, 2014; Ezcurra & Butler, 2015a; Ezcurra & Butler, 2015b).

Charig & Reig (1970) recognized the suborder Proterosuchia as composed of two families: Proterosuchidae (“Chasmatosaurus”-like forms) and Erythrosuchidae (Erythrosuchus-like forms). These authors included Archosaurus, “Chasmatosaurus”, Chasmatosuchus, “Elaphrosuchus,” and Proterosuchus within the Proterosuchidae, and Garjainia, Erythrosuchus, “Vjushkovia,” Shansisuchus, and possibly Cuyosuchus within the Erythrosuchidae. Accordingly, Charig & Reig (1970) considered Shansisuchidae, Garjainiidae and Vjushkoviidae as junior synonyms of Erythrosuchidae, and Chasmatosauridae as a junior synonym of Proterosuchidae. Charig & Reig (1970) considered the proterosuchids as a primitive stock of “thecodonts” from which erythrosuchids evolved. In particular, “Elaphrosuchus” was depicted as more closely related to erythrosuchids than were other proterosuchids (Charig & Reig, 1970: Fig. 6). Subsequently, Bonaparte (1982) proposed a more inclusive suborder “Proterosuchia,” being composed of two distinct infraorders: Proterochampsia and “Rauisuchia.” Within Proterochampsia, Bonaparte (1982) included Proterosuchidae, Cerritosauridae and Proterochampsidae, whereas “Rauisuchia” was composed of Erythrosuchidae and Rauisuchidae. From the late 1970s to early 1990s, multiple Early and Middle Triassic archosauriforms were described from Australia, Russia and China (Camp & Banks, 1978; Ochev, 1979; Ochev, 1980; Thulborn, 1979; Cheng, 1980; Wu, 1981; Peng, 1991; Sennikov, 1992; Sennikov, 1994), and most were assigned to either Proterosuchidae or Erythrosuchidae following the “Chasmatosaurus”-like and Erythrosuchus-like dichotomy.

Benton (1985) reported the first cladistic analysis that included early archosauriforms, although it still was not a numerical (fully explicit) approach. Benton (1985) placed Proterosuchus fergusi either within “Prolacertiformes” or as the sister-taxon of his concept of Archosauria (which in Benton’s usage was a non-crown-group clade including Erythrosuchus, Euparkeria, and “later archosaurs”), with Erythrosuchus africanus recovered as the sister-taxon to all other archosaurs. The first numerical cladistic analysis to include proterosuchians was that of Gauthier (1986), who employed Proterosuchidae to root the tree in which he found Erythrosuchidae as the sister-taxon of Proterochampsidae + Archosauria. Gauthier (1986: 42) restricted the usage of the term Archosauria to the crown group, and Gauthier, Kluge & Rowe (1988) erected the new group Archosauriformes for the clade including all the descendants of the most recent common ancestor of Proterosuchidae, Erythrosuchidae, Proterochampsidae and Archosauria. Several subsequent analyses recovered broadly similar topologies to that of Gauthier (1986), including those of Benton & Clark (1988), Sereno & Arcucci (1990), Sereno (1991), Parrish (1993), Gower (2002) and Benton (2004), but the paraphyly of “Proterosuchia” in these studies was the outcome of choices (implicit or explicit) in rooting and not a result of the analyses (other than that erythrosuchids lie outside of non-proterosuchid, non-erythrosuchid archosauriforms when trees are rooted with proterosuchids). Juul (1994) and Bennett (1996) were the first authors to include both Proterosuchidae and Erythrosuchidae as part of the ingroup in numerical analyses, and, as a consequence, to test the phylogenetic position of proterosuchids among archosauromorphs. The analyses of Juul (1994) and Bennett (1996) recovered proterosuchids and erythrosuchids as successive outgroups of all other archosauriforms, though proterosuchids and erythrosuchids were each represented either as a suprageneric taxon or by a single species, such that the monophyly of Proterosuchidae and Erythrosuchidae were not tested. Parrish (1992) reported an analysis that included six proterosuchian species and an aggregate “other archosauriforms” in the ingroup and Proterosuchus as an outgroup. Within his monophyletic Erythrosuchidae, Shansisuchus shansisuchus, Erythrosuchus africanus, Garjainia prima and Fugusuchus hejiapensis were successive outgroups of a monophyletic “Vjushkovia,” comprising “Vjushkoviatriplicostata (=Garjainia triplicostata) and “Vjushkoviasinensis (=Youngosuchus sinensis) (Fig. 5A).

Figure 5: Phylogenetic trees depicting selected previous hypotheses of relationships for “Proterosuchia.”

(A) Single most parsimonious tree of Parrish (1992); (B) strict reduced consensus tree of Gower & Sennikov (1997); (C) single most parsimonious tree of Dilkes & Sues (2009); (D) strict consensus tree of Ezcurra, Lecuona & Martinelli (2010); and (E) strict consensus tree of Nesbitt (2011). Bremer support (= Decay Index) values greater than one are indicated below each node (support values for the trees of Parrish (1992) and Gower & Sennikov (1997) were calculated using the original data matrices). Abbreviations: Erythr., Erythrosuchidae; Protero., Proterosuchidae. Bold font indicates putative proterosuchians.

Gower & Sennikov (1996) reported a cladistic analysis based only on braincase characters, in which proterosuchians were recovered as monophyletic. Among proterosuchians, distinct proterosuchid and erythrosuchid clades were recognized, with Fugusuchus hejiapensis as well as Proterosuchus fergusi found as members of Proterosuchidae (contra Parrish, 1992). Xilousuchus sapingensis, “Vjushkoviatriplicostata, Erythrosuchus africanus, and Shansisuchus shansisuchus were recovered as members of Erythrosuchidae (Gower & Sennikov, 1996). Within Erythrosuchidae, Gower & Sennikov (1996) found sister-taxon relationships for Xilousuchus sapingensis and “Vjushkoviatriplicostata, and for Erythrosuchus africanus and Shansisuchus shansisuchus. Gower & Sennikov (1997) added non-braincase characters and included a different taxon sampling and recovered a paraphyletic “Proterosuchia,” with erythrosuchids more closely related to Archosauria than to proterosuchids (Fig. 4B). Proterosuchus fergusi was found as sister-taxon to the other putative proterosuchids Fugusuchus hejiapensis and Sarmatosuchus otschevi. Additionally, in contrast to the earlier study of Gower & Sennikov (1996), Xilousuchus sapingensis was recovered as an erythrosuchid in only some of their most parsimonious trees (Gower & Sennikov, 1997). Gower & Sennikov (2000) conducted a review of the Permo–Triassic archosauriforms from Russia and concluded that “Vjushkovia” was a junior synonym of Garjainia, in agreement with previous comments by Kalandadze & Sennikov (1985), Ochev & Shishkin (1988) and Sennikov (1995a) and Sennikov (1995b), and that Garjainia triplicostata was probably also a junior synonym of Garjainia prima.

Recent work by Dilkes & Sues (2009) found results that differ from most previous phylogenetic analyses. Although Proterosuchus fergusi was recovered as the sister-taxon of all other archosauriforms, Euparkeria capensis was found as the sister-taxon of Erythrosuchus africanus and more crownward archosauriforms (Fig. 5C). Thus, Dilkes & Sues (2009) recovered a polyphyletic (rather than the more usual paraphyletic) “Proterosuchia.” Subsequent revision of this dataset by Dilkes & Arcucci (2012) recovered a paraphyletic “Proterosuchia.” Ezcurra, Lecuona & Martinelli (2010) described the new early archosauriform Koilamasuchus gonzalezdiazi and expanded the taxonomic and character sample of the data matrix of Dilkes & Sues (2009), including characters employed in several previous archosauriform phylogenetic analyses (e.g., Dilkes, 1998; Gower & Sennikov, 1997). Among taxa sampled by Ezcurra, Lecuona & Martinelli (2010), the taxonomic content of Proterosuchidae hypothesized by previous authors (e.g., Proterosuchus, Sarmatosuchus and Fugusuchus: Gower & Sennikov, 1997) was recovered as paraphyletic (or even polyphyletic because the specimen that it is now the holotype of Koilamasuchus gonzalezdiazi was interpreted originally as a proterosuchid: Bonaparte, 1981), and the previously hypothesized content of Erythrosuchidae (Erythrosuchus africanus, Shansisuchus shansisuchus, Garjainia triplicostata) was recovered as monophyletic (Fig. 5D). Ezcurra, Lecuona & Martinelli (2010) recovered Proterosuchus fergusi as sister-taxon to all other sampled archosauriforms, with Sarmatosuchus otschevi and Fugusuchus hejiapensis (considered as proterosuchids by Gower & Sennikov, 1996; Gower & Sennikov, 1997; Gower & Sennikov, 2000) being more closely related to other archosauriforms than to Proterosuchus fergusi. Ezcurra, Lecuona & Martinelli (2010) also recovered Koilamasuchus gonzalezdiazi and the proposed euparkeriid Osmolskina czatkowicensis (Borsuk-Białynicka & Evans, 2003) as successive outgroups of Erythrosuchidae and more crownward archosauriforms. Erythrosuchidae was recovered as the sister-group of Euparkeria capensis and more crownward archosauriforms, in contrast to the results of Dilkes & Sues (2009) but in agreement with most other quantitative phylogenetic analyses of Archosauriformes (e.g., Juul, 1994; Bennett, 1996; Gower & Sennikov, 1997; Nesbitt et al., 2009; Nesbitt, 2011). Within Erythrosuchidae, Ezcurra, Lecuona & Martinelli (2010) recovered Shansisuchus shansisuchus as the sister-taxon of Erythrosuchus africanus + “Vjushkovia” (=Garjainia) triplicostata, contrasting with the internal relationships of Erythrosuchidae found by Gower & Sennikov (1996). Desojo, Ezcurra & Schultz (2011) obtained broadly similar results to those of Ezcurra, Lecuona & Martinelli (2010) using a similar data matrix.

Nesbitt (2011) recovered Erythrosuchus africanus and Proterosuchidae as successive outgroups of all non-proterosuchian archosauriforms, resembling most previous numerical analyses. Nesbitt (2011: 249) was the first to include the oldest known archosauriform, Archosaurus rossicus, in a numerical phylogenetic analysis and found it to be the sister-taxon of Proterosuchus fergusi within a monophyletic Proterosuchidae (Fig. 5E). Nesbitt (2011) and Nesbitt, Liu & Li (2011) reinterpreted the Chinese taxon Xilousuchus sapingensis, once considered a member of “Proterosuchia” (see above), as a poposauroid archosaur, a hypothesis followed by recent authors (e.g., Butler et al., 2011). Ezcurra, Scheyer & Butler (2014) revised the Permian saurian record and conducted a phylogenetic analysis including several basal archosauromorphs. These authors found Proterosuchus fergusi and Archosaurus rossicus within a monophyletic Proterosuchidae, in agreement with Nesbitt (2011) (Fig. 3B). The enigmatic Permian diapsid Eorasaurus olsoni was recovered in a polytomy together with Erythrosuchus africanus and Euparkeria capensis, thus potentially representing the oldest known archosauriform (Ezcurra, Scheyer & Butler, 2014). More recently, Nesbitt et al. (2015) included the Chinese archosauriform “Chasmatosaurusyuani for the first time in a quantitative phylogenetic analysis and recovered it within Proterosuchidae, being the sister-taxon of Proterosuchus spp. (Fig. 3C).

In summary, the systematic history of proterosuchians was chaotic through most of the 20th century, but the advent of numerical phylogenetic techniques gave rise to near-unanimous consensus regarding the non-monophyly of “Proterosuchia” (but see Gower & Sennikov, 1996), with erythrosuchids being more closely related to Archosauria than to proterosuchids. However, this stability may be superficial because few proterosuchian species have been included in numerical phylogenetic analyses. Furthermore, the taxonomic contents and internal relationships of Proterosuchidae and Erythrosuchidae have not yet been tested thoroughly. It is important to note that quantitative support for many of the previously recovered relationships among putative proterosuchids and erythrosuchids is low in terms of decay indices, and that topology-based statistical tests of the (non)monophyly of Proterosuchidae, Erythrosuchidae and Proterosuchia have not been carried out. The phylogenetic analysis presented here is intended to shed light on these issues.

Materials and Methods

Objectives and taxonomic sample

The aim of the present phylogenetic analysis is to generate a comprehensive higher-level phylogenetic hypothesis of basal archosauromorphs and shed light on the species-level interrelationships of taxa historically identified as proterosuchian archosauriforms (i.e., taxa usually considered as members either of Proterosuchidae or Erythrosuchidae; Charig & Reig, 1970; Charig & Sues, 1976; Ezcurra, Butler & Gower, 2013). As a result, the taxonomic sample is mainly focused on non-archosaurian archosauromorphs and, more specifically, on proterosuchians, which range chronostratigraphically from the upper Permian (Archosaurus rossicus) to the Upper Triassic (Cuyosuchus huenei). Six non-archosauromorph diapsids were included as outgroups: the early diapsid Petrolacosaurus kansensis, the basal neodiapsids Youngina capensis and Acerosodontosaurus piveteaui, and the early lepidosauromorphs Paliguana whitei, Planocephalosaurus robinsonae and Gephyrosaurus bridensis. All of these taxa have been consistently recovered outside Archosauromorpha in recent phylogenetic analyses (Müller, 2004; Bickelmann, Müller & Reisz, 2009; Reisz, Laurin & Marjanović, 2010; Ezcurra, Scheyer & Butler, 2014), and, as a whole, provide an exhaustive sample of early diapsid character states. The late Carboniferous Petrolacosaurus kansensis has been repeatedly found to be more distantly related to archosauromorphs than are Youngina capensis, Acerosodontosaurus piveteaui, and lepidosauromorphs (Müller, 2004; Senter, 2004; Bickelmann, Müller & Reisz, 2009; Reisz, Modesto & Scott, 2011; Ezcurra, Scheyer & Butler, 2014) and therefore was chosen here to root the phylogenetic trees.

The taxonomic sample of non-archosauriform archosauromorphs is chosen in order to test the higher-level phylogenetic relationships between relatively well-established groups (e.g., Rhynchosauria, Tanystropheidae) and several species with problematic affinities, such as several taxa usually assigned to the likely non-monophyletic “Prolacertiformes.” A total of 19 taxa previously identified as non-archosauriform archosauromorphs are included, including three tanystropheids (Macrocnemus bassanii, Amotosaurus rotfeldensis, Tanystropheus longobardicus), six rhynchosaurs (Noteosuchus colletti, Mesosuchus browni, Howesia browni, Eohyosaurus wolvaardti, Rhynchosaurus articeps, Bentonyx sidensis), eight taxa identified previously as protorosaurs/prolacertiforms (Aenigmastropheus parringtoni, Protorosaurus speneri, Prolacertoides jimusarensis, Boreopricea funerea, Jesairosaurus lehmani, Prolacerta broomi, Kadimakara australiensis, Eorasaurus olsoni), and three allokotosaurians (Pamelaria dolichotrachela, Trilophosaurus buettneri, Azendohsaurus madagaskarensis). Non-proterosuchian archosauriforms are represented by 38 taxa, including four doswelliids (Archeopelta arborensis, Tarjadia ruthae, Jaxtasuchus salomoni, Doswellia kaltenbachi), all known proterochampsid species (see Trotteyn, Arcucci & Raugust, 2013), four basal phytosaurs (Parasuchus agustifrons, Parasuchus hislopi, Nicrosaurus kapffi, Smilosuchus spp.), seven basal ornithodirans (Dimorphodon macronyx, Lagerpeton chanarensis, Marasuchus lilloensis, Lewisuchus admixtus, Silesaurus opolensis, Heterodontosaurus tucki, Herrerasaurus ischigualastensis), two ornithosuchids (Ornithosuchus longidens, Riojasuchus tenuisceps), seven basal suchians (Aetosauroides scagliai, Gracilisuchus stipanicicorum, Turfanosuchus dabanensis, Prestosuchus chiniquensis, Batrachotomus kupferzellensis, Nundasuchus songeaensis, Yarasuchus deccanensis), and five archosauriforms that seem not to fit into any of the aforementioned clades (Euparkeria capensis, Asperoris mnyama, Dorosuchus neoetus, Dongusuchus efremovi, Vancleavea campi). Smilosuchus spp. is scored as a supraspecific terminal because the taxonomy of this phytosaur taxon is currently problematic, although it appears to represent a monophyletic genus (Stocker, 2010; Stocker & Butler, 2013).

The preferred option here was to sample suprageneric taxa using multiple species-level terminals rather than a composite suprageneric terminal because it has been shown by previous authors that the former method considerably outperforms the latter in both simulations and empirical data (Wiens, 1998; Prendini, 2001; Jenner, 2006; Brusatte, 2010). As a result, basal representatives of each clade were sampled (e.g., Noteosuchus colletti, Mesosuchus browni, Howesia browni and Eohyosaurus wolvaardti for rhynchosaurs; Lagerpeton chanarensis, Marasuchus lilloensis, and Lewisuchus admixtus for ornithodirans; Parasuchus angustifrons and Parasuchus hislopi for phytosaurs) as well as species that represent a balance between completeness (thus maximising phylogenetic data) and a relatively basal position in the lineage (e.g., Rhynchosaurus articeps and Bentonyx sidensis for rhynchosaurs; Silesaurus opolensis, Heterodontosaurus tucki and Herrerasaurus ischigualastensis for ornithodirans; Aetosauroides scagliai, Gracilisuchus stipanicicorum, Turfanosuchus dabanensis, Prestosuchus chiniquensis, Batrachotomus kupferzellensis and Nundasuchus songeaensis for suchians).

The proterosuchian sample is intended to be the most comprehensive of the data set, representing a total of 32 terminals that sample all currently valid nominal species (Ezcurra, Butler & Gower, 2013). The holotype of Proterosuchus fergusi (SAM-PK-591) was considered undiagnostic by Ezcurra & Butler (2015a), but this specimen is included as an independent terminal in order to test its phylogenetic position. It is noteworthy that a number of proterosuchian species are included here for the first time in a quantitative phylogenetic analysis, namely “Blomosuchus georgii,” Vonhuenia friedrichi, “Ankistrodon indicus,” Proterosuchus alexanderi, Proterosuchus goweri, Kalisuchus rewanensis, Chasmatosuchus rossicus, “Gamosaurus lozovskii,” “Exilisuchus tubercularis,” Uralosaurus magnus, Shansisuchus kuyeheensis, Cuyosuchus huenei, Guchengosuchus shiguaiensis, Chalishevia cothurnata and Garjainia madiba. Also included are an unnamed taxon represented by isolated dorsal vertebrae from the Early Triassic of southeastern Australia (Kear, 2009), a partial skeleton of a small erythrosuchid from the Cynognathus Assemblage Zone (AZ) of South Africa that was previously considered possibly referable to Erythrosuchus africanus (Gower, 2003), and the probable pseudosuchian “Dongusia colorata” (Gower & Sennikov, 2000). Several species included in the taxonomic sample of the analysis are currently considered as nomina dubia (e.g., “Ankistrodon indicus,” “Gamosaurus lozovskii,” “Dongusia colorata”; Charig & Reig, 1970; Charig & Sues, 1976; Gower & Sennikov, 2000; Ezcurra, Butler & Gower, 2013), but they were included in this data matrix to test their original phylogenetic interpretation and the taxonomic content of Proterosuchidae and Erythrosuchidae. “Crenelosaurus nigrosilvanus,” “Ocolurtaia arquata,” “Seemannia palaeotriadica,” and “Shansisuchus heiyuekouensis” represent four poorly informative proterosuchian species considered nomina dubia (Gower & Sennikov, 2000; Ezcurra, Butler & Gower, 2013) and, as a result, are not included in the analysis. A specifically indeterminate occurrence of “Chasmatosaurus” from the earliest Triassic of India (Satsangi, 1964) is also based on very fragmentary bones and is not also included.

The assignment of the referred specimens of Kadimakara australiensis, Garjainia madiba and Uralosaurus magnus is problematic (see below Remarks about these species) and, as a result, the holotype and the complete hypodigm (i.e., type and referred specimens) of these species were scored as independent terminals. The aim of these independent scorings is to test the effect that the referred material of the hypodigm has on the phylogenetic relationships of the species. Following a similar logic, Chasmatosuchus magnus (=“Jaikosuchus magnus”) and “Gamosaurus lozovskii” were scored as independent terminals in a first analysis and were merged into a single terminal in a second analysis because they are considered here subjective synonyms between each other (see below Remarks about these species). These alternative scorings allow the hypothesis of synonymy to be tested.

The first-hand study of Archosaurus rossicus, “Blomosuchus georgii,” Vonhuenia friedrichi, Chasmatosuchus magnus (=“Jaikosuchus magnus”), “Gamosaurus lozovskii,” Dorosuchus neoetus, Dongusuchus efremovi and Kalisuchus rewanensis as part of this research resulted in modifications to their taxonomy and/or casted doubts about the composition of their hypodigms (see Remarks about these species below). The specimens that have been used for the scorings of these species are summarized as follows: (i) Archosaurus rossicus and (ii) Kalisuchus rewanensis are scored based only on their holotypes; (iii) “Blomosuchus georgii” is scored based on its holotype and an isolated parabasisphenoid previously referred to Vonhuenia friedrichi (PIN 1025/14); (iv) Vonhuenia friedrichi is scored based on its holotype and a referred cervical vertebra (PIN 1025/419); (v) Chasmatosuchus magnus is scored based on its holotype; (vi) “Gamosaurus lozovskii” is scored based on its holotype and five referred vertebrae (PIN 3361/14, 94, 183, 213, 214); (vii) Dorosuchus neoetus is scored based on its type series; and (viii) Dongusuchus efremovi is scored based on its holotype and four unambiguously referred isolated femora.

The resultant taxonomic list of the data matrix is composed of 96 independent taxa, plus the holotype of Proterosuchus fergusi, three hypodigms that partially overlap with the scorings of their respective holotypes (Kadimakara australiensis, Garjainia madiba, and Uralosaurus magnus) and two species that are probably synonyms (“Gamosaurus lozovskii” and Chasmatosuchus magnus) (i.e., 102 operational taxonomic units). The vast majority of species included in the archosauromorph taxonomic sample are Triassic in age, with the exception of four late Permian (Aenigmastropheus parringtoni, Archosaurus rossicus, Eorasaurus olsoni, and Protorosaurus speneri) and three Early Jurassic (Gephyrosaurus bridensis, Dimorphodon macronyx, and Heterodontosaurus tucki) species.

Operational taxonomic units

The terminals used in this phylogenetic analysis are listed as follows.

Petrolacosaurus kansensis Lane, 1945 (OUTGROUP)

Age. Kasimovian–Gzhelian, Late Pennsylvanian, latest Carboniferous (Reisz, 1977; Reisz & Berman, 1986).

Locality. Garnett Quarry, Missourian Series, Anderson County, Kansas, midwest USA (Reisz, 1977; Reisz & Berman, 1986).

Stratigraphic horizon. Rock Lake Member, Stanton Formation, Lansing Group (Reisz, 1977; Reisz & Berman, 1986).

Holotype. KUVP 1424: partial right hindlimb of an adult individual.

Referred material. Multiple immature and mature specimens housed in KUPV and listed by Reisz (1981: 4, 5).

Diagnosis. Early diapsid distinguished from other diapsids on the basis of the following unique combination of characters: well developed supratemporal and infratemporal fenestrae and elongate; narrow suborbital fenestra; parietal without posterolateral process; posterior splenial bone present; marginal dentition unusually thin-walled; six elongate cervical vertebrae; a pair of mammillary processes on the neural spine of first sacral vertebra; large dorsal ischiadic notch; slender forelimbs equal in length to more massive hindlimb; and propodials equal in length to epipodials (Reisz, 1981: 4).

Remarks. Petrolacosaurus kansensis is one of the oldest and more completely known early diapsid (Reisz, 1977) and has been usually included as one of the outgroups in phylogenetic analyses focused on the internal relationships of neodiapsids or basal saurians (e.g., Benton, 1985; Jalil, 1997; Dilkes, 1998; Modesto & Reisz, 2002; Senter, 2004; Modesto & Sues, 2004; Pritchard et al., 2015). Comprehensive osteological descriptions of this species were published by Peabody (1952) and Reisz (1981).

Acerosodontosaurus piveteaui Currie, 1980

Age. Wuchiapingian–Changhsingian, late Permian (Currie, 1980).

Locality. Sakamena River Valley, Tulear, southern Madagascar (Currie, 1980).

Stratigraphic horizon. Lower Sakamena Formation, Sakamena Group (Currie, 1980).

Holotype. MNHN 1908-32-57: partial skeleton of an immature individual mostly preserved as natural moulds in a single concretion preserving part and counterpart (Currie, 1980). The skeleton lacks the anterior portion of the snout, left side of the skull, braincase, tail, most of the pectoral girdle, left manus, left hindlimb, and lower part of the right hindlimb.

Emended diagnosis. Early neodiapsid distinguished from other diapsids on the basis of the following unique combination of character-states: ventrally open infratemporal fenestra; quadratojugal absent; at least 36 tooth positions in the maxilla and 34 in the dentary; cleithrum present; radius twisted; ulna lacking an ossified olecranon; and pubis with long tubercle (modified from Bickelmann, Müller & Reisz, 2009).

Remarks. Acerosodontosaurus piveteaui was originally described by Currie (1980) and more recently redescribed by Bickelmann, Müller & Reisz (2009). The only known specimen consists of natural, well-preserved moulds that provide a very good anatomical record of the postcranial axial skeleton of early neodiapsids.

Youngina capensis Broom, 1914

Age. Capitanian-Changhsingian, latest middle to late Permian (Rubidge et al., 2013).

Localities. New Bethesda, Graaff-Reinet, Eastern Cape Province, South Africa (type locality; Gow, 1975; Smith & Evans, 1996; Gardner, Holliday & O’Keefe, 2010).

Stratigraphic horizons. Dicynodon AZ, Balfour Formation, Karoo Supergroup, and referred specimens have been also collected in the Tropidostoma AZ of the Middelton and Balfour formations, Karoo Supergroup, South Africa (Gow, 1975; Smith & Evans, 1996; Gardner, Holliday & O’Keefe, 2010).

Holotype. AMNH 5561: skull and vertebrae.

Referred material. Multiple specimens housed in the United States and South Africa, and listed by Gow (1975: 90). Subsequently, the following specimens were referred to Youngina capensis, SAM-PK-K10818: cluster of disarticulated juvenile skeletons (Smith & Botha-Brink, 2014); SAM-PK-K10777: anterior skull and lower jaws with some postcranial bones (Smith & Botha-Brink, 2014); SAM-PK-K6205: partial skull; SAM-PK-K7578: dorsoventrally compressed skull; SAM-PK-K7710: an aggregation of five fairly complete to more fragmentary skeletons belonging to immature individuals (Smith & Evans, 1996); SAM-PK-K8565: partial skeleton; GHG K106: dorsoventrally compressed skull and lower jaws; and GHG RS160: partial skull.

Emended diagnosis. Early neodiapsid distinguished from other diapsids on the basis of the following unique combination of character-states: quadratojugal closing the infratemporal fenestra ventrally; long posterolateral process of the frontal; a pair of tabular bones; robust stapes bearing a stapedial foramen; parabasisphenoid with thick parasphenoid crests; radius twisted; ulna lacking an ossified olecranon; pelvic girdle lacking a thyroid fenestra; and metatarsal V with an outer process.

Remarks. Multiple juvenile to adult specimens of Youngina capensis have been collected in the last century and this species represents the most comprehensively studied Permian neodiapsid (Broom, 1914; Broom, 1921; Broom, 1922; Gow, 1975; Currie, 1981; Evans, 1987; Smith & Evans, 1996; Gardner, Holliday & O’Keefe, 2010). Youngina capensis has been repeatedly used in quantitative phylogenetic analyses as a key terminal to reconstruct the ancestral character-states of Sauria (e.g., Benton & Allen, 1997; Dilkes, 1998; Senter, 2004; Gottmann-Quesada & Sander, 2009; Ezcurra, Scheyer & Butler, 2014; Pritchard et al., 2015).

Paliguana whitei Broom, 1903b

Age. Induan–?early Olenekian, Early Triassic (Damiani et al., 2000; Rubidge, 2005; Lucas, 2010).

Locality. Donnybrook, between Tarkastad and Queenstown, South Africa (Carroll, 1975; Kitching, 1977; Groenewald & Kitching, 1995).

Stratigraphic horizon. Lystrosaurus AZ, upper Balfour Formation or lower Katberg Formation, Beaufort Group, Karoo Supergroup (Carroll, 1975; Kitching, 1977; Groenewald & Kitching, 1995).

Holotype. AM 3585: partial skull and lower jaw.

Emended diagnosis. Early saurian distinguished from other diapsids on the basis of the following unique combination of characters-states: at least some maxillary crowns with a convex distal margin; elongated and continuously dorsally curved anterior process of the jugal; anteroventrally oriented ventral process of the squamosal; well-exposed supratemporal fossa medial to the supratemporal fenestra on the parietal; and a quadrate conch.

Remarks. Paliguana whitei historically has been considered as the oldest known lepidosauromorph because of the presence of a quadrate conch (Evans & Borsuk-Białynicka, 2009; Evans & Jones, 2010). This species was recently included for the first time in a quantitative phylogenetic analysis and its position within Lepidosauromorpha was supported (Ezcurra, Scheyer & Butler, 2014). The holotype and only known specimen of Paliguana whitei has been recently further prepared (W De Klerk, pers. comm., 2012) and new information from the palatal region of the skull is available. Unfortunately, the poor state of preservation of these regions hampers the determination of several anatomical features (AM 3585).

Planocephalosaurus robinsonae Fraser, 1982

Age. Rhaetian, Late Triassic (Whiteside & Marshall, 2008).

Locality. Cromhall quarry, south Gloucestershire, UK (Fraser, 1982).

Stratigraphic horizon. Karstic fissures in Dinantian Limestones (Fraser, 1982).

Holotype. AUP No. 11061: left maxilla.

Referred material. Approximately 750 bones housed in the AUP (see Fraser, 1982; Fraser & Walkden, 1984) and the NHMUK PV.

Diagnosis. Early rhynchocephalian distinguished from other diapsids on the basis of the following unique combination of character-states: incomplete lower temporal bar; frontals and parietals fused; broad and flat parietal table with a large central pineal foramen; no supratemporal or lacrimal; deep overlap of the pterygoid and quadrate; quadrate and quadratojugal fused; quadrate foramen present; premaxilla paired; vomers with small scattered teeth; pterygoid with two tooth rows; no teeth on the transverse ramus of the pterygoid; palatines with two rows of conical teeth parallel to the marginal dentition; dentition acrodont; all teeth are radially ribbed; dentary with a posterior process that articulates with the articular complex; and no splenial (Fraser, 1982).

Remarks. Planocephalosaurus robinsonae is one of the best-known early rhynchocephalian lepidosauromorphs and possesses an intermediate morphology between more basal saurians and more advanced members of Rhynchocephalia, such as the species of Clevosaurus (Fraser, 1982; Evans & Jones, 2010). This species has been used in previous higher-level phylogenetic analyses as a representative of the early morphological diversity of Lepidosauromorpha (e.g., Reisz, Laurin & Marjanović, 2010). Planocephalosaurus robinsonae was described in detail by Fraser (1982) and Fraser & Walkden (1984).

Gephyrosaurus bridensis Evans, 1980

Age. Hettangian–Sinemurian, Early Jurassic (Harris, 1957; Kermack, 1975; Kermack, Mussett & Rigney, 1981).

Locality. Pontalun quarry, near Bridgend in South Glamorgan, Wales, UK (Evans, 1980).

Stratigraphic horizon. Lower Liassic fissure infills (Evans, 1980).

Holotype. UCL T.1503: right dentary.

Referred material. More than 1,000 specimens housed in the UCL (see Evans, 1980; Evans, 1981).

Diagnosis. Early rhynchocephalian distinguished from other diapsids on the basis of the following unique combination of character-states: incomplete lower temporal bar and a fixed quadrate; frontals and parietals unpaired; no supratemporal; reduced lacrimal; postfrontal and postorbital discrete elements; exoccipitals normally fused to basioccipital; no fenestra rotunda; quadrate with broad median lamina; quadratojugal reduced and fused to quadrate conch; quadrate foramen present; quadrate head supported in a ventromedial flange of the squamosal; squamosal large and tetradiate with a ventral process holding quadrate; premaxillae paired; well developed palatal dentition but no teeth on parasphenoid or pterygoid flange; dentition pleurodont; dentary has posterior process articulating with articular complex; dentary closes Meckelian fossa in midregion; low coronoid process; partial fusion of articular, surangular and angular; no splenial; amphicoelous notochordal vertebrae; primitive zygosphene/zygantrum; intercentra present throughout column; single headed ribs on all presacral vertebrae except first few cervicals; atlas and axis with ribs; caudal fracture planes; T-shaped interclavicle; scapula and coracoid fused to form a solid plate; humerus with both ectepi- and entepicondylar foramina; pelvic girdle with large thyroid fenestra; large fourth distal tarsal; hooked fifth metatarsal; gastralia present (Evans, 1980: 204, 205).

Remarks. Gephyrosaurus bridensis is currently considered as the sister-taxon of all remaining rhynchocephalian lepidosauromorphs (Evans & Jones, 2010) and, as a result, it is a key taxon to sample early lepidosauromorph morphological diversity. As for Planocephalosaurus robinsonae, this species has been used as a representative of Lepidosauromorpha in previous higher-level phylogenetic analyses (e.g., Senter, 2004; Pritchard et al., 2015). Gephyrosaurus bridensis was described in detail by Evans (1980) and Evans (1981).

Cteniogenys Gilmore, 1928, Cteniogenys sp. (sensu Evans, 1989)

Age. Late Bathonian, Middle Jurassic (Freeman, 1976; Evans, 1990).

Locality. The Old Cement Works quarry, Kirtlington, Oxfordshire, UK (Evans, 1989).

Stratigraphic horizon. Kirtlington Mammal Bed, near the base of the Forest Marble (Evans, 1989).

Material. More than a hundred of mainly isolated cranial and postcranial bones housed in the NHMUK PV (see Evans, 1990; Evans, 1991).

Diagnosis. The genus Cteniogenys was diagnosed by Evans (1989: 582) by the following features: dentary with double lateral rows of sensory foramina with posteriorly directed grooves; dentary with dorsal and ventral splenial facets that taper anteriorly and end well behind the symphysis, leaving the anterior part of the Meckelian fossa opening medially; medially directed symphysis of the lower jaw with the bulk of the symphysial surface along the upper margin of the Meckelian fossa; subthecodont tooth implantation; broad conical teeth with striations confined to the upper part of the crown and more prominent lingually.

Remarks. Cteniogenys antiquus is the type species of the genus and is known from the Upper Jurassic Morrison Formation of Wyoming, USA (Gilmore, 1928). A second species, Cteniogenys reedi, was described from the Late Jurassic of Guimarota, Portugal (Seiffert, 1970; Seiffert, 1973), but was considered more recently a junior synonym of the type species (Estes, 1983). Subsequently, cranial and postcranial remains from a Middle Jurassic microvertebrate site in Oxfordshire, England, were referred to Cteniogenys sp. (Evans, 1989; Evans, 1990; Evans, 1991).These specimens were left unassigned at the species level because of the age difference of at least 15 million years between the British specimens and those from Portugal and North America (Evans, 1989). Most of the cranial and posctcranial anatomy of the Cteniogenys material from Oxfordshire is known and has been described by Evans (1990) and Evans (1991). The scorings of Cteniogenys sp. in the present phylogenetic analysis are based only on the Middle Jurassic specimens from Oxfordshire.

Simoedosaurus lemoinei Gervais, 1877

Age. Thanetian, late Paleocene (Sigogneau-Russell, 1985).

Locality. Mouras Quarry, Cernay-Berru, Marne, France (Sigogneau-Russell, 1985).

Neotype. MNHN BR 1935: left half of a dorsolaterally crushed skull that lacks the braincase.

Referred material. Multiple specimens housed in the MNHN and SMNS collections (see Sigogneau-Russell & Russell, 1978; Sigogneau-Russell, 1981)

Diagnosis. Medium-sized choristoderan that differs from other diapsids in the following combination of features: snout narrow and represents about 40% of the total length of the skull; internal choanae situated in the posterior half of the snout; lacrimal short; contact between postorbitofrontal and parietal situated approximately at the level of the anterior edge of the supratemporal fenestra; premaxillary teeth very large; maxillary teeth large anteriorly and very small at the posterior end of the tooth row (Sigogneau-Russell, 1985: 766).

Remarks. Simoedosaurus lemoinei is the only post-Jurassic terminal included in the taxonomic sample of this phylogenetic analysis. It was chosen to represent the morphology of choristoderans because it is one of the best known and described members of this enigmatic clade of neodiapsids. Simoedosaurus lemoinei was described in detail by Sigogneau-Russell & Russell (1978) and Sigogneau-Russell (1981).

Aenigmastropheus parringtoni Ezcurra, Scheyer & Butler, 2014

Age. Middle–late Wuchiapingian, middle late Permian (Angielczyk et al., 2014).

Locality. Locality B35 of Stockley, close to the road near Ruanda, Songea District, Ruhuhu Valley, southern Tanzania (Ezcurra, Scheyer & Butler, 2014).

Stratigraphic horizon. Usili Formation (formerly Kawinga Formation), Songea Group, Ruhuhu Basin (Ezcurra, Scheyer & Butler, 2014).

Holotype. UMZC T836: partial postcranial skeleton including five posterior cervical–anterior dorsal vertebrae, distal half of the right humerus, fragment of probable left humeral shaft, proximal end of the right ulna, and three indeterminate fragments of bone (one of which may represent part of a radius) (Ezcurra, Scheyer & Butler, 2014).

Diagnosis. Archosauromorph distinguished from other diapsids on the basis of the following unique combination of character-states (autapomorphy marked with an asterisk): posterior cervical and anterior dorsal vertebrae notochordal, with well-developed anterior and posterior centrodiapophyseal and prezygodiapophyseal laminae, and sub-triangular neural spines in lateral view; humerus with a strong diagonal ridge on the anterior surface of the shaft*; humerus with strongly developed capitellum (radial condyle) and trochlea (ulnar condyle) and without entepicondylar and ectepicondylar foramina; ulna with strongly developed olecranon process forming a single ossification with the rest of the bone (Ezcurra, Scheyer & Butler, 2014: 15, 16).

Remarks. Parrington (1956) described the remains of what he considered “an enigmatic reptile” from the Lopingian of Tanzania. He concluded that this specimen (UMZC T836) did not bear close resemblances to any known synapsid, and suggested instead that the specimen might have close affinities with archosaurs because of the vertebral morphology and the presence of hollow limb bones and an ectepicondylar groove on the humerus. Subsequently, Hughes (1963) noted that the vertebrae of UMZC T836 were not as archosaurian in appearance as Parrington originally thought and that laminae on the neural arch also occur in pelycosaurian synapsids. Gower & Sennikov (2000) noted that UMZC T836 is probably indeterminate, but could possibly be archosaurian. Most recently, Ezcurra, Butler & Gower (2013) indicated that UMZC T836 is likely not referable to Archosauriformes. Ezcurra, Scheyer & Butler (2014) redescribed in detail the anatomy of UMZC T386 and considered that it possessed a unique combination of apomorphies that allowed the erection of a new genus and species: Aenigmastropheus parringtoni. These authors included Aenigmastropheus parringtoni for the first time in a quantitative phylogenetic analysis and recovered it at the base of Archosauromorpha, within a clade composed of Protorosaurus speneri and tanystropheids. Nevertheless, Ezcurra, Scheyer & Butler (2014) stated that further tests on the phylogenetic position of this species should be conducted in the future with an improved character and taxonomic sample of early archosauromorphs. Indeed, Ezcurra, Scheyer & Butler (2014) pointed out that the presence of notochordal vertebrae may place Aenigmastropheus parringtoni as the most basal known archosauromorph.

Protorosaurus speneri Meyer, 1832

Age. Middle Wuchiapingian, middle late Permian (Legler, Gebhardt & Schneider, 2005; Legler & Schneider, 2008; Ezcurra, Scheyer & Butler, 2014).

Localities. Glücksbrunn, Thuringia, Germany (type locality; Gottmann-Quesada & Sander, 2009). Referred specimens were recovered in several localities within Thuringia and Hesse, central Germany. Protorosaurus also occurs at Middridge and Quarrington quarries near Durham, England, UK (Evans & King, 1993; Gottmann-Quesada & Sander, 2009). For a full list of the German localities, see Gottmann-Quesada & Sander (2009: Table 1).

Stratigraphic horizons. Kupferschiefer Formation, Zechstein Group, basal cycle of the Zechstein (Z1) in Germany (type horizon) and Marl Slate Formation in the UK (Ezcurra, Scheyer & Butler, 2014).

Lectotype. NHMW 1943I4: almost complete skeleton missing the skull (Gottmann-Quesada & Sander, 2009).

Referred material. Multiple fairly complete to fragmentary skeletons housed in several European institutions. The complete hypodigm of Protorosaurus speneri was listed by Gottmann-Quesada & Sander (2009: 137, Table 1).

Emended diagnosis. Archosauromorph distinguished from other diapsids on the basis of the following unique combination of character-states (autapomorphies marked with an asterisk): premaxilla with three tooth positions; frontal-nasal suture transverse; squamosal posterior process extends posterior to the head of the quadrate; surangular-angular suture anteroposteriorly convex ventrally in lateral view; distinct mammillary processes on the lateral surface of the neural spine extend up to the tenth presacral*; middle and distal caudal vertebrae with bifurcated neural spine*; coracoid with large biceps process; ulna with olecranon process as a separate ossification; and femoral shaft diameter distally narrowed.

Remarks. Protorosaurus speneri is by far the best-known Permian archosauromorph, being represented by multiple individuals from marine beds of Europe. A fairly complete skeleton of this species provides the best available evidence of a Permian archosauromorph body plan (Gottmann-Quesada & Sander, 2009; Ezcurra, Scheyer & Butler, 2014). The anatomy of Protorosaurus speneri has been recently described in detail by Gottmann-Quesada & Sander (2009). This species has been alternatively recovered in quantitative phylogenetic analyses within a monophyletic Protorosauria (together with tanystropheids; e.g., Benton, 1985; Dilkes, 1998; Ezcurra, Scheyer & Butler, 2014), as one of the sister-taxa of tanystropheids and more crownward archosauromorphs (Gottmann-Quesada & Sander, 2009), or the most basal archosauromorph (Pritchard et al., 2015). Therefore, despite the rather complete knowledge of the anatomy of Protorosaurus speneri, its phylogenetic position among archosauromorphs is still much debated.

Macrocnemus bassanii Nopcsa, 1930

Age. Late Anisian–early Ladinian, Middle Triassic.

Localities. Besano, Italy (type locality); Monte San Giorgo, Switzerland.

Stratigraphic horizons. Scisti bituminosi, Besano Formation, Italy (type horizon); Alla Cascina Member, Meride Limestone Formation, Switzerland.

Holotype. MSNM specimen Besano I (probably destroyed during WWII): partial skeleton including skull, complete vertebral column, humerus, tibia and fibula.

Referred material. Several specimens housed in the collections of MSNM and PIMUZ (see Peyer, 1937; Rieppel, 1989a).

Emended diagnosis. Small tanystropheid that differs from other archosauromorphs in the following combination of features: anteriorly curved, “U”-shaped suture between frontal and parietal in dorsal view; posterolateral processes of the parietal strongly posterolaterally oriented; marginal teeth recurved, with posteriorly concave distal margin; 24 presacral vertebrae; humerus less than 10% longer than radius; and tibia and fibula at least 20% longer than femur. This diagnosis is composed of the synapomorphies of the genus Macrocnemus found by Pritchard et al. (2015) and the differences reported by Li, Zhao & Wang (2007) and Fraser & Furrer (2013) between Macrocnemus bassanii and Macrocnemus fuyuanensis and Macrocnemus obristi, respectively.

Remarks. Macrocnemus bassanii is a tanystropheid known from several rather complete skeletons that lack the extremely long necks present in more deeply nested members of the group (e.g., Tanystropheus longobardicus, Tanytrachelos ahynis) (Peyer, 1937). Peyer (1937) provided a detail description of the species, which was partially complemented by Rieppel (1989a). Macrocnemus bassanii was repeatedly used as a representative member of Tanystropheidae in phylogenetic analyses (e.g., Dilkes, 1998; Senter, 2004; Gottmann-Quesada & Sander, 2009) and recently has been recovered as the basalmost tanystropheid together with the congeneric species Macrocnemus fuyuanensis (Pritchard et al., 2015).

Amotosaurus rotfeldensis Fraser & Rieppel, 2006

Age. Early Anisian, early Middle Triassic.

Locality. Kossig quarry, Rotfelden, in district of Calw, Germany (Fraser & Rieppel, 2006).

Stratigraphic horizon. Röt Formation, ‘Violet horizon 5’ of Ortlam (1967), Upper Buntsandstein (Fraser & Rieppel, 2006).

Holotype. SMNS 50830: partial skull, cervical series, scattered dorsal vertebrae, and pectoral and pelvic elements (Fraser & Rieppel, 2006).

Referred material. Multiple slabs preserving partially articulated cranial and postcranial bones, including SMNS 50691, 54783, 54784a, 54784b, 54810, 90540, 90543, 90544, 90552, 90559, 90563, 90564, 90566, 90599–90601 and several unnumbered specimens.

Diagnosis. Amotosaurus rotfeldensis is a small tanystropheid that was diagnosed by Fraser & Rieppel (2006: 867) on the basis of the following features: eight cervical vertebrae; the centra of cervicals 4 and 5 are the longest and are at least 2.5 times as long as their minimum height; elongate cervical ribs extending across at least three intervertebral articulations anteriorly; 25 presacral vertebrae; second sacral rib distinctly bifurcate; length of metatarsals asymmetric with IV being the longest, then III, then II, then I and V being the shortest; proximal phalanx on digit V elongate and ‘metatarsal-like’; three distal tarsals in the ankle; the ischium and pubis almost touch below the level of the thyroid fenestra; the vomers, palatines and pterygoids are all covered by a fine shagreen of denticles.

Remarks. Wild (1980) interpreted multiple tanystropheid specimens from the Middle Triassic of the Black Forest (southwest Germany) as juveniles of “Tanystropheusantiquus (Wild, 1980), but this hypothesis was subsequently questioned by several authors who suggested that they may belong to a new genus (e.g., Evans, 1988; Wild, 1987). Fraser & Rieppel (2006) revised the taxonomy of these specimens and concluded that they belong to a new genus and species, Amotosaurus rotfeldensis. Fraser & Rieppel (2006) thus considered the new species distinct from “Tanystropheusantiquus, which was subsequently transferred to the new genus Protanystropheus by Sennikov (2011), resulting in the new combination Protanystropheus antiquus. Fraser & Rieppel (2006) described briefly the anatomy of Amotosaurus rotfeldensis and a detailed description of the species is needed. Based on limited character data, Pritchard et al. (2015) found Amotosaurus rotfeldensis as more closely related to Tanystropheus longobardicus than to other sampled tanystropheids. My examination of available specimens of Amotosaurus rotfeldensis allowed me to score a vast number of characters that were not described or figured in the original description of the species. However, a detailed description of Amotosaurus rotfeldensis would require further preparation of multiple specimens and is beyond the scope of the present paper.

Tanystropheus longobardicus (Bassani, 1886)

Age. Late Anisian–early Ladinian, Middle Triassic.

Localities. Besano, Varese Province, Lombardy, Italy (type locality; Bassani, 1886); Monte San Giorgo, Valporina, Switzerland (neotype locality; Wild, 1973).

Stratigraphic horizons. Besano Formation, Italy (type horizon; Bassani, 1886); Meride Formation, Switzerland (neotype horizon; Wild, 1973).

Neotype. PIMUZ T 2791: fairly complete and partially articulated skeleton of a probably young individual that lacks the distal half of the tail (Wild, 1973).

Referred material. Dozens of juvenile and adult specimens housed in the collections of MSNM, PIMUZ and SMNS (see lists of specimens in Wild, 1973; Nosotti, 2007).

Emended diagnosis. Large tanystropheid that differs from other archosauromorphs in the following combination of features: frontals flared laterally as wing-like structures above the orbits; large pineal foramen enclosed beween frontals and parietals; ventrally flexed anterior end of dentary; strongly posteriorly developed retroarticular process of the lower jaw; conical and straight marginal tooh crowns with longitudinal ridges; 13 cervical vertebrae; length of the centra of the fourth and fifth cervical vertebrae at least 14 times their heights; distal end of second sacral rib not bifurcated; two ossified distal carpals; and manual digit IV composed of four phalanges.

Remarks. The genus Tanystropheus and species Tanystropheus conspicuus were erected by Meyer (1847–1855) based on isolated bones from the European Upper Muschelkalk, which were interepreted as strongly elongated caudal vertebrae of a reptile. Subsequently, Bassani (1886) named the new genus and species Tribelesodon longobardicus based on cranial and postcranial remains from the Middle Triassic of Besano (Italy), interpreting it as a flying reptile (Nopsca, 1923). Peyer (1931) described new specimens of Tanystropheus from Monte San Giorgo (Switzerland) and reinterpreted the elongated type bones of Tanystropheus conspicuus as cervical vertebrae. In addition, Peyer (1931) proposed that Tribelesodon and Tanystropheus were cogeneric, referred all the specimens from Besano and Monte San Giorgio to Tanystropheus longobardicus, and designated Tanystropheus longobardicus as the type species of the genus. Peyer (1931) reinterpreted Tanystropheus as a terrestrial reptile with an extremely long neck adapted to catch prey from the shore of water bodies. Wild (1973) provided a detailed description of Tanystropheus longobardicus, and the anatomical knowledge of the species was further improved by Nosotti (2007) with the description of new specimens. Tanystropheus longobardicus has been commonly included in the taxonomic sampling of phylogenetic analyses focused on early archosauromorph interrelationships and represents the best-known tanystropheid (e.g., Benton, 1985; Dilkes, 1998; Gottmann-Quesada & Sander, 2009; Ezcurra, Scheyer & Butler, 2014; Pritchard et al., 2015).

Jesairosaurus lehmani Jalil, 1997

Age. Late Olenekian–Anisian, Early to Middle Triassic (Lehman, 1971; Jalil & Taquet, 1994).

Locality. Site 5003 of Busson, east Algeria (Jalil, 1997).

Stratigraphic horizon. Lower sandstones of the lower Zarzaïtine Formation, Zarzaitine Series (Jalil, 1997).

Holotype. ZAR 06: skull, neural arches of the last five cervical vertebrae, pectoral girdle and proximal end of the left humerus (modified from Jalil, 1997).

Referred material. ZAR 07: partial, dorsoventrally compressed skull; ZAR 08: partial skull and postcranium; ZAR 09: two partial postcranial skeletons preserved in the same block (ZAR 09A is a skull originally articulated with one of the postcraniums of ZAR 09 and prepared by serial grinding); ZAR 10: poorly preserved scapula and at least four dorsal vertebrae; ZAR 11: pelvic girdle, at least three dorsal and three caudal vertebrae and some gastralia; ZAR 12: poorly preserved pelvic girdle and at least five dorsal and three caudal vertebrae; ZAR 13: seven articulated presacral vertebrae (ZAR 13A is a pelvic girdle originally articulated to ZAR 13 and prepared by serial grinding); ZAR 14: pelvic girdle; and ZAR 15: pelvic girdle and partial hindlimb (modified from Jalil, 1997).

Emended diagnosis. Small archosauromorph that differs from other diapsids in the following combination of features: posterior process of the maxilla well developed and forming most of the ventral border of the orbit; extensive contact between palatine and maxilla; ascending process of the jugal well developed extending posteriorly to the posterior border of the orbit and contacting or lying close to the squamosal; postfrontal subequal in size to the postorbital; small pineal foramen restricted to and enclosed by the anterior end of the parietals; palatal teeth not arranged in distinct rows; neck anteroposteriorly shorter than the skull; basioccipital with a faint median keel on the ventral surface; middle and posterior dorsal vertebrae with anteroposteriorly or posteriorly expanded distal ends of the neural spines; scapulacoracoid inverted L-shape in lateral view, with a strongly posteriorly developed coracoid; humerus with apparently fully closed ectepicondylar foramen; pubis and ischium of the hemipelvis fused to each other; and hindlimb longer than forelimb and relatively large in comparison with the rest of the postcranial skeleton (modified from Jalil, 1997: 508).

Remarks. Jesairosaurus lehmani was described in detail by Jalil (1997). Despite its short neck, this species has been considered since its original description as a member of “Prolacertiformes.” Nevertheless, the phylogenetic position of this species has not been further tested in more recent quantitative analyses. Some comments on the anatomy of the species are added here that are informative for the phylogenetic analyses conducted here. The holotype specimen (ZAR 06) is a partial skull with articulated lower jaw. In this specimen, the anterior end of the dentary and its symphysis are complete and, as a result, the premaxillae should be fairly complete. The right premaxilla preserves six teeth in place, but there is room in the alveolar margin of the bone for nine to ten tooth positions (ZAR 06), resembling the high premaxillary tooth count present in some basal saurians (e.g., Gephyrosaurus bridensis: Evans, 1980). The anterodorsal margin of the maxilla is strongly concave and there is no evidence for a facet for reception of a postnarial process of the premaxilla. The lateral surface of the anterior process of the maxilla possesses a large, oval foramen at the level of the third maxillary tooth, which seems to be homologous with the anterior maxillary foramen of other saurians (e.g., Planocephalosaurus robinsonae: NHMUK PV R9954; Protorosaurus speneri: Gottmann-Quesada & Sander, 2009; Prolacerta broomi: Modesto & Sues, 2004). A row of smaller neurovascular foramina extends posteriorly, posterior to the level of the third maxillary tooth position. A total of 20 or 21 tooth positions are estimated in the maxillae of ZAR 06. The maxillary tooth crowns are straight, with convex mesial and distal margins in labial view. The teeth are not fused to the tooth bearing bones and they possess long roots, indicating that they were deeply implanted in the sockets (ZAR 06, 09). In one specimen (ZAR 09) there is a distinct medial wall to the alveoli and, as a result, the tooth implantation was probably subthecodont.

Figure 6: Jesairosaurus lehmani.
Partial skull of a referred specimen (ZAR 07) in dorsal view, and close up of the pineal foramen and frontal–parietal suture. Numbers indicate character-states scored in the data matrix and the arrow indicates anterior direction. Abbreviations: ax, axis; fr, frontal; or, orbit; pfr, prefrontal; po, postorbital; sq, squamosal; stf, supratemporal fenestra. Scale bar equals 5 mm.

The quadrate is shallowly emarginated posteriorly and lacks the distinct lateral projection of its anterior magin that characterizes the quadrate conch of lepidosauromorphs (Gauthier, Kluge & Rowe, 1988). The pineal foramen is small and oval, with an anteroposterior main axis, and is mostly or probably completely enclosed by both parietals (contra Jalil, 1997) (Fig. 6). The parietal lacks a dorsal emargination on the posterior margin of the posterolateral process (ZAR 06, 08), contrasting with the condition in other basal archosauromorphs (Müller, 2004). The paroccipital process of the opisthotic is laterally well developed and contacts extensively with the posterolateral process of the parietal. As a result, the posttemporal fenestra was very small, if it was present. The anterior end of the dentary curves gently ventrally and medially, resembling the condition in Gephyrosaurus bridensis (Evans, 1980) and Protorosaurus speneri (Gottmann-Quesada & Sander, 2009). The lateral surface of the dentary of ZAR 06 possesses four neurovascular foramina aligned in a mainly longitudinal row. There is at least one posterior dentary tooth that possesses a gentle mesiodistal constriction between the crown and the root in ZAR 08.

A total number of nine cervical vertebrae can be estimated based on the position of the pectoral girdle with respect to the axial skeleton in ZAR 06. All the neural spines exposed in ZAR 06 are anterodorsally oriented, as occurs in the eighth and ninth cervical vertebrae of ZAR 08. By contrast, the probable sixth and seventh cervicals of ZAR 08 possess vertical neural spines. This intraspecific variation in the orientation of the cervical neural spines resembles that present among specimens of Proterosuchus fergusi (GHG 231, SAM-PK-11208, K140). There is no fossa immediately lateral to the base of the neural spine in the cervicals of ZAR 08 and the cervical neural spines lack a transverse distal expansion or mammillary processes in ZAR 06 and ZAR 08. The seventh cervical neural spine of ZAR 08 possesses an anteroposteriorly expanded distal end, with an acute anterior projection.

The dorsal series is represented by 15 vertebrae in ZAR 08. There is no evidence of laminae on the dorsal neural arches in the available specimens (e.g., ZAR 11, 12). The dorsal vertebrae lack fossae immediately lateral to the base of the neural spine in two specimens (ZAR 08, 09), but they are present as deep, subcircular pits in another specimen (ZAR 13). The neural spines of the middle dorsal vertebrae possess a strong posterior projection of their distal end (ZAR 08), whereas an anterior projection is variable in the two individuals assessed as ZAR 09. The distal ends of the neural spines may have contacted each other and lack a transverse expansion of the distal and mammillary processes (ZAR 09, 13). Broken dorsal centra show an internal structure composed of trabeculae, but there is no large, central opening that would indicate the presence of a notochordal canal (ZAR 13). The same condition was observed in the postcranial axial series of other specimens and, as a result, the vertebrae of Jesairosaurus lehmani are reinterpreted here as not notochordal (contra Jalil, 1997).

Three probable sternal plates are preserved immediately posterior to the coracoids and posterolateral to the posterior ramus of the interclavicle in ZAR 09. The right sternal plate is preserved as a mould and the two left elements are preserved as poorly mineralized elements aligned anteroposteriorly to each other. The sternal plates are oval, with a transversely oriented main axis. Two of the sternal plates are paired in the transverse plane and seem to have had a median longitudinal contact. As described by Jalil (1997), the ectepicondylar foramen of the humerus appears to have been fully closed (ZAR 09).

The proximal articular surface of the femur is convex in ventral view, suggesting a rather well ossified head (ZAR 14), contrasting with the flat or concave and poorly ossified proximal end present in rhynchosaurs (e.g., Mesosuchus browni: SAM-PK-7416; Stenaulorhynchus stockleyi: Huene, 1938), Prolacerta broomi (BP/1/2675), Proterosuchus fergusi (SAM-PK-140) and erythrosuchids (e.g., Erythrosuchus africanus: NHMUK PV R3592). The presence of an internal or fourth trochanter is equivocal (ZAR 14) and the distal end of the femur does not taper distally in side view (ZAR 15), contrasting with the condition in Protorosaurus speneri (SMNS 55387, cast of Simon/Bartholomäus specimen) and tanystropheids (Amotosaurus rotfeldensis: SMNS 54783). The proximal tarsals were not described by Jalil (1997), but they are present in ZAR 15, although poorly preserved, and it can be at least determined that the calcaneum lacks a calcaneal tuber. It is not possible to assess the presence or absence of a perforating foramen between the proximal tarsals.

Pamelaria dolichotrachela Sen, 2003

Age. Anisian, early Middle Triassic (Lucas, 2010).

Localities. Three adjacent sites about 4 kilometres north–northwest of the Yerrapalli village, Adilabad district, Andhra Pradesh, India (Sen, 2003).

Stratigraphic horizon. Yerrapalli Formation, Gondwana Supergroup, Pranhita-Godavari Basin (Sen, 2003).

Holotype. ISI R316: partial cranial and postcranial skeleton (Sen, 2003).

Referred material. ISI R317: partial cranial, presacral series and some appendicular bones; ISI R318–333: isolated bones found in association with the holotype of Yarasuchus deccanensis (Sen, 2003; Sen, 2005).

Diagnosis. Pamelaria dolichotrachela is a medium-sized basal archosauromorph that was diagnosed by Sen (2003: 664) on the basis of the following features: external naris small and confluent; vomer posteriorly wide; ventrally directed plate-like process of prootic anterior to ventral ramus of opisthotic; coronoid process prominent; dentary with approximately 19 teeth; and additional spinous projection placed anteriorly with abrupt shift in the position of neural spine in the posterior caudals.

Remarks. Sen (2003) originally erected and described Pamelaria dolichotrachela as a prolacertiform archosauromorph. More recently, Nesbitt et al. (2015) recovered this species as the most basal member of Allokotosauria. Sen (2003) provided a good account of the anatomy of the species, but a revised description and updated comparisons with other allokotosaurians would improve the anatomical knowledge of Pamelaria dolichotrachela. A detailed revision of the anatomy of this species is beyond the scope of this contribution and is currently in preparation by the author and colleagues.

Azendohsaurus madagaskarensis Flynn et al., 2010

Age. Late Ladinian–early Carnian, late Middle Triassic–early Late Triassic (Nesbitt et al., 2015).

Locality. Drainage of the Malio River, southwestern Madagascar (Flynn et al., 2010; Nesbitt et al., 2015).

Stratigraphic horizon. Basal ‘Isalo II’ of Besairie (1972), termed the Makay Formation by Razafimbelo (1987); Morondava Basin (Flynn et al., 2010; Nesbitt et al., 2015).

Holotype. UA 7-20-99-653 (field number 7-20-99-653): a nearly complete skull with associated vertebrae (Flynn et al., 2010).

Paratypes. FMNH PR 2751 (field number 8-30-98-376), nearly complete disarticulated skull (associated with postcranial specimens FMNH PR 2788, FMNH PR 2789, FMNH PR 2792 and possibly FMNH PR 2796) (Nesbitt et al., 2015).

Referred material. Around 300 specimens that preserve cranial and postcranial bones and were listed by Nesbitt et al. (2015: Appendix 1).

Diagnosis. Azendohsaurus madagaskarensis is a medium-sized (2–3 m in length), early-diverging archosauromorph that differs from all other archosauromorphs in possessing the following unique combination of character-states: ventral curvature of the anterior portion of the dentary; a robust dorsal process of the maxilla, the base of which occurs on the anterior third of the bone; a concave anterior margin of the dorsal process of the maxilla; lanceolate teeth with denticles; a series of small nutrient foramina on the medial surface of the maxilla; elongated cervical vertebrae with small epipophyses dorsal to the postzygapophyses; small tuber located on the ventrolateral surface of the prezygapophyseal stalk in the middle to posterior cervical vertebrae; deep fossae between well developed laminae in the posterior cervical vertebrae; hyposphene-hypantra intervertebral articulations in the posterior cervical, anterior trunk, and sacral vertebrae; well-defined fossa at the base of the neural spine, just posterior to the prezygapophyses in the second sacral vertebra; oval and proximodistally oriented tuber on the lateral surface of the scapula that nearly contacts the edge of the glenoid fossa; posteriorly expanded, T-shaped interclavicle; lateral side of the calcaneal tuber expanded laterally and ventrally, with the ventral expansion being clearly visible in proximal view; and proximal projection on the proximal surface of metatarsal IV (Flynn et al., 2010; Nesbitt et al., 2015).

Remarks. Azendohsaurus laaroussii was named by Dutuit (1972) based on teeth and tooth-bearing elements from the Argana Formation of Morocco. Dutuit (1972) identified Azendohsaurus laaroussii as an ornithischian dinosaur, but it subsequently was reidentified as a sauropodomorph dinosaur (Thulborn, 1973; Bonaparte, 1976; Gauffre, 1993; Flynn et al., 1999). Flynn et al. (2010) named the new species Azendohsaurus madagaskarensis from the Makay Formation of Madagascar and the remains of this species provided for the first time a comprehensive knowledge of the cranial anatomy of the genus. This new information allowed Flynn et al. (2010) to reinterpret Azendohsaurus laaroussii as a non-archosaurian archosauromorph rather than an herbivorous dinosaur. More recently, Nesbitt et al. (2015) described in detail the postcranial anatomy of Azendohsaurus madagaskarensis and, as a result, this species is currently one of the best-known early archosauromorphs. Nesbitt et al. (2015) included both species of Azendohsaurus in a phylogenetic analysis and recovered them as members of the new clade Allokotosauria, which was found as the sister-taxon of the clade composed of Prolacerta broomi and Archosauriformes.

Trilophosaurus buettneri Case, 1928

Age. Middle Norian to possibly Rhaetian; late Late Triassic (Parker & Martz, 2011).

Localities. Near Walker’s Tank, Texas, USA (type locality; Case, 1928); multiple localities that belong to several late Upper Triassic formations in Texas, New Mexico and Arizona, southwest USA (Long & Murry, 1995; Spielmann et al., 2008).

Stratigraphic horizons. Tecovas Formation (type horizon; Case, 1928) and several other late Upper Triassic formations (see Long & Murry, 1995; Spielmann et al., 2008).

Holotype. UMMP 2338: an incomplete right dentary fragment bearing parts of five teeth.

Referred material. Hundreds of specimens composed of cranial and postcranial remains that were listed by Spielmann et al. (2008: Appendix 1).

Diagnosis. Spielmann et al. (2008: 11) diagnosed the genus Trilophosaurus as an archosauromorph that can be distinguished from all other archosauromorphs by its transversely broad, tricuspid teeth and a femur with a prominent internal trochanter that extends one-third of the way down the shaft. In addition, Spielmann et al. (2008: 11) distinguished Trilophosaurus buettneri from Trilophosaurus jacobsi by the lack of prominent cingula linking the cusps both labiolingually across the center of the tooth and also along the mesial and distal margins of the tooth; central cusp subequal in height to the labial and lingual cusps; central cusp not displaced labially or lingually, so tooth crown is labiolingually symmetrical in occlusal view; skull possessing a single parasaggital crest; cervical vertebrae with bifurcate postzygapophyses; procoelous cervical centra; double keeled sacral centra; a lack of prominent ridges on the sacral vertebrae extending from the posterior margin of the pre- and postzygapophyses to the base of the neural spine; sacral neural spines extend nearly the entire length of the centra; rectangular ectepicondyle; radial condyle of humerus larger than ulnar condyle; proximal femur is rhombus-shaped; astragalus with pointed calcaneal articular surface; ridge developed on posterior astragalus; and “neck” of astragalus gracile and elongate.

Remarks. Trilophosaurus buettneri was named by Case (1928) based on a partial dentary bearing labiolingually broad, tricuspid teeth. Subsequently, more complete specimens and partial skeletons were collected from the Triassic of the southwest USA and Gregory (1945) described in detail the anatomy of the species. The cranial anatomy of Trilophosaurus buettneri was revised by Parks (1969) and Spielmann et al. (2008) redescribed and figured comprehensively the anatomy of the species. More recently, Nesbitt et al. (2015) reinterpreted and redescribed the carpal and hand anatomy of Trilophosaurus buettneri. This species has been frequently included in phylogenetic analyses focused on early archosauromorphs, but its position among the main lineages of the group has been a matter of debate. Trilophosaurus buettneri has been alternatively recovered as one of the most basal archosauromorphs (Benton, 1985), the sister-taxon of rhynchosaurs (Gottmann-Quesada & Sander, 2009), the sister-taxon of the clade composed of rhynchosaurs, Prolacerta broomi and archosauriforms (Dilkes, 1998; Ezcurra, Scheyer & Butler, 2014), or the sister-taxon of Prolacerta broomi and archosauriforms (Pritchard et al., 2015). More recently, Nesbitt et al. (2015) recovered Trilophosaurus buettneri as closely related to Azendohsaurus within the new clade Allokotosauria. Trilophosaurus buettneri and other allokotosaurians were recovered as the sister-taxon of Prolacerta broomi and archosauriforms by Nesbitt et al. (2015).

Noteosuchus colletti Watson, 1912a

Age. Induan, earliest Triassic (Carroll, 1976).

Locality. Near Grassy Ridge, Eastern Cape Province, South Africa (Watson, 1912a; Carroll, 1976).

Stratigraphic horizon. Base of the Lystrosaurus AZ, Katberg Formation, Tarkastad Subgroup, Beaufort Group, Karoo Supergroup, Karoo Basin (Watson, 1912a; Carroll, 1976).

Holotype. AM 3591: partial postcranium, missing the neck, pectoral girdle, right forelimb and distal half of the tail. The vast majority of the bones of the specimen were mechanically destroyed in order to study their natural moulds (Carroll, 1976).

Emended diagnosis. Small rhynchosaur that differs from other basal archosauromorphs in the following unique combination of features: second sacral rib bifurcated distally, with a tapering posterolateral process (squared in Mesosuchus browni); anterior caudal vertebrae with a neural spine 2.1 times dorsoventrally taller than their anteroposterior length at base (ratio equals 3.0–3.5 in Mesosuchus browni); manual unguals considerably longer than preungual phalanges; ilium without preacetabular process (small preacetabular process in Mesosuchus browni) and postacetabular process mainly posteriorly oriented (posterodorsally oriented in Mesosuchus browni); and length of metatarsal I around 0.40 times the length of metatarsal III.

Remarks. Dilkes (1998) suggested that Noteosuchus colletti is potentially a subjective junior synonym of the rhynchosaur Mesosuchus browni from the early Anisian of South Africa. This potential synonymy was based on the presence of a consistent morphology between both species and the shared features of a median ventral groove on the centra of the first two caudal vertebrae and a flattened first distal tarsal (Dilkes, 1998). Noteosuchus colletti has been largely ignored in discussions of rhynchosaur evolution (e.g., Benton, 1983; Benton, 1990; Wilkinson & Benton, 1995; Hone & Benton, 2008; Montefeltro et al., 2013; Mukherjee & Ray, 2014). Ezcurra, Scheyer & Butler (2014) scored Noteosuchus colletti and Mesosuchus browni as independent terminals in their phylogenetic analysis because the temporal gap between the two species apparently spans most of the Early Triassic (ca. 5 million years) and the former species could potentially shed light on the minimal divergence time of Rhynchosauria. Ezcurra, Scheyer & Butler (2014) recovered Noteosuchus colletti and Mesosuchus browni within Rhynchosauria in a trichotomy with Howesia browni, and a consistent result was recovered by Ezcurra, Montefeltro & Butler (2016) using an independent dataset. Ezcurra, Montefeltro & Butler (2016) revisited some anatomical features of Noteosuchus colletti and highlighted differences between the sacral and caudal vertebrae and ilium of this species and those of Mesosuchus browni (e.g., tapering posterolateral process of the distally bifurcated second sacral rib, proportionally lower neural spines of the anterior caudal vertebrae, absence of preacetabular process and posterodorsally oriented postacetabular process on the ilium), which support the hypothesis that Noteosuchus colletti is a valid taxon.

Mesosuchus browni Watson, 1912b

Age. Early Anisian, early Middle Triassic (Rubidge, 2005).

Locality. Site along a road between Aliwal North and Lady Grey (exact location of the site unknown), Eastern Cape Province, South Africa (Dilkes, 1998).

Stratigraphic horizon. Burgersdorp Formation, Cynognathus AZ subzone B, Tarkastad Subgroup, Beaufort Group, Karoo Supergroup, Karoo Basin (Dilkes, 1998).

Holotype. SAM-PK-5882: partial snout, palate, braincase, lower jaws, sections of articulated presacral vertebral column, nine articulated caudal vertebrae, portions of scapula and pelvic girdle, and partial forelimb and hindlimbs (Dilkes, 1998).

Referred material. SAM-PK-6046: incomplete right maxilla, an articulated series of the last ten presacrals, both sacrals, and first six caudals, partial forelimbs, left and right pelvic girdles, right hindlimb, elements of left tarsus; SAM-PK-6536: virtually complete skull with lower jaws, articulated cervical vertebrae and ribs, dorsal vertebrae and ribs, complete left scapulocoracoid and partial right scapula, interclavicle, clavicles, distal end of left humerus, and gastralia; SAM-PK-7416: an articulated vertebral column composed of the last dozen presacrals, both sacrals and at least the first 15 caudal vertebrae, fragments of right forelimb, pelvic girdle, complete right femur, right crus and partial left crus, and right and left tarsi and pedes (Dilkes, 1998).

Diagnosis. Dilkes (1998: 503) diagnosed Mesosuchus browni on the basis of the following autapomorphies: multiple rows of maxillary and dentary teeth with each row consisting of only a very small number of teeth; two premaxillary teeth that are approximately twice the size of the maxillary teeth; maxillary teeth inset medially and project below the internal naris; occlusion between vomerine teeth and dentary teeth; saddle-shaped vomers that overhang dorsally the premaxillary symphysis; length of axis neural spine greater than length of axis centrum; anteroposteriorly narrow neural spine of third cervical; and prominent midventral groove on first two caudal centra.

Remarks. Mesosuchus browni is the best-known non-rhynchosaurid rhynchosaur species (Dilkes, 1998) and has been used as a representative of rhynchosaur morphology in higher-level phylogenetic analyses focused on archosauromorphs (e.g., Dilkes, 1998; Gottmann-Quesada & Sander, 2009; Ezcurra, Scheyer & Butler, 2014; Pritchard et al., 2015) and to root the comprehensive phylogenetic analysis focused on early archosauriforms of Nesbitt (2011). Mesosuchus browni possesses an intermediate morphology between that of non-rhynchosaurian basal archosauromorphs and that of later rhynchosaurs, lacking, for example, the distinct blade and groove dental apparatus that is characteristic of rhynchosaurids (Dilkes, 1998). This species was described in detail by Dilkes (1998).

Howesia browni Broom, 1905

Age. Early Anisian, early Middle Triassic (Rubidge, 2005).

Locality. Unknown locality near the town of Aliwal North, Eastern Cape Province, South Africa (Dilkes, 1995).

Stratigraphic horizon. Burgersdorp Formation, Cynognathus AZ subzone B, Tarkastad Subgroup, Beaufort Group, Karoo Supergroup, Karoo Basin (Dilkes, 1995).

Holotype. SAM-PK-5884: partial skull with palate and incomplete lower jaws (Dilkes, 1995).

Referred material. SAM-PK-5885: dorsoventrally crushed skull with partial palate, braincase and atlas-axis complex; SAM-PK-5886: partial, articulated postcranium consisting of the posterior four dorsal, both sacral and first dozen caudal vertebrae, incomplete pelvic girdle, partial left hindlimb, and complete right tarsus (Dilkes, 1995).

Diagnosis. Dilkes (1995: 666) diagnosed Howesia browni as a small rhynchosaur diapsid characterized by the following autapomorphies: multiple rows of small, conical teeth with ankylothecodont implantation in medially expanded maxillae that lack longitudinal, occlusal grooves; multiple rows of numerous conical teeth on the dentaries; broad ventral process of squamosal that does not extend below middle of infratemporal fenestra; horizontal shelf on medial side of quadrate ramus of pterygoid; contact between ectopterygoid and jugal reduced to less than half of the length of the distal expansion of the ectopterygoid; deep pockets on neural arches of posterior dorsal and sacral vertebrae; and tall, posteriorly inclined neural spines of proximal caudal vertebrae.

Remarks. Howesia browni is a non-rhynchosaurid rhynchosaur from the Cynognathus AZ that is less well known than Mesosuchus browni (Dilkes, 1995; Dilkes, 1998). Howesia browni contrasts with the latter species in the presence of a medially expanded maxillary tooth plate, bearing multiple tooth rows, as occurs in rhynchosaurids (Dilkes, 1995). This species was described in detail by Dilkes (1995) and its tarsal anatomy was previously revised by Carroll (1976). The whereabouts of a pectoral girdle and a humerus described by Broom (1906) are currently unknown for SAM-PK-5885 (Dilkes, 1995), and the only available information for these elements is the original description of the species by Broom (1906).

Eohyosaurus wolvaardti Butler et al., 2015

Age. Early Anisian, early Middle Triassic (Rubidge, 2005).

Locality. Farm Lemoenfontein 44, Rouxville District, Free State Province, South Africa (Butler et al., 2015).

Stratigraphic horizon. Burgersdorp Formation, Cynognathus AZ subzone B, Tarkastad Subgroup, Beaufort Group, Karoo Supergroup, Karoo Basin (Butler et al., 2015).

Holotype. SAM-PK-K10159: partial skull missing the anterior end, with associated incomplete lower jaw and two partial limb bones, one of them preserved as a natural mould (Butler et al., 2015).

Diagnosis. Eohyosaurus wolvaardti is a small rhynchosaur that was diagnosed by Butler et al. (2015: 575) by the following autapomorphy: jugal with elongate dorsal process that forms the entire anterior margin of the infratemporal fenestra and that articulates anteriorly with the entire posterior margin of an elongate ventral process of the postorbital. In addition, Butler et al. (2015) distinguished this species from other rhynchosaurs on the basis of the following unique combination of character-states: maxillae and dentaries mediolaterally expanded; teeth present on the occlusal and lingual surfaces of the maxillae and dentaries; maxilla lacks a longitudinal occlusal groove and dentary lacks occlusal blade; occlusal margin of maxilla offset ventrally from the ventral margin of the main body of the jugal; presence of a short anguli oris crest on the lateral surface of the maxilla; posterior process of jugal is short and terminates at approximately 50% of the anteroposterior length of the infratemporal fenestra; elongate posterior process of the postorbital terminates above the anterior margin of the ventral process of the squamosal; elongate ventral process of the squamosal extends for more than 50% of the posterior margin of the infratemporal fenestra; and sagittal crest on parietal.

Remarks. Butler et al. (2015) named Eohyosaurus wolvaardti based on a single, partial skull and two partial limb bones (one preserved as a natural mould). This species was recovered as the sister-taxon of Rhynchosauridae (i.e., Rhynchosaurus articeps and more advanced rhynchosaurs), thus partially bridging the morphological gap between the other early rhynchosaurs from the Cynognathus AZ of South Africa and rhynchosaurids (Butler et al., 2015).

Rhynchosaurus articeps Owen, 1842

Age. Anisian, early Middle Triassic (Benton et al., 1994; Lucas, 2010).

Locality. Grinshill quarry, north of Shrewsbury, central England, UK (Benton, 1990; Benton & Spencer, 1995).

Stratigraphic horizon. Tarporley Siltstone Formation (Benton, 1990).

Lectotype. SHYMS 1: nearly complete skull and mandible.

Paralectotype. SHYMS 2: anterior part of a postcranium, including dorsal vertebrae and ribs, right scapula and coracoid, interclavicle, and right humerus.

Referred material. SHYMS 3: nearly complete skull, cervical and dorsal vertebrae and ribs, some gastralia, left coracoid, left forelimb, and partial left hindlimb; SHYMS 4: part and counterpart of a partial postcranium, including cervical and dorsal vertebrae and ribs, gastralia, right scapula and forelimb, part of the pelvic girdle and hindlimbs; SHYMS 5: fragments of dorsal vertebrae and ribs, gastralia, partial right pelvic girdle, fragments of left femur and complete right hindlimb; SHYMS 6: dorsal vertebrae and ribs, partial right pectoral girdle, right forelimb and possible skin impressions; SHYMS 7: partial right ischium, anterior caudal vertebrae and proximal end of right femur; SHYMS G3851: a sequence of anterior–middle caudal vertebrae and ribs; SHYMS G07537: an articulated series of posterior dorsal, sacral and anterior caudal vertebrae; NHMUK PV R1236: nearly complete skull and mandible; NHMUK PV R1237: partial skull and mandible that goes with the postcranium NHMUK PV R1238; NHMUK PV R1238: partial postcranium that misses left forelimb and hindlimb and tail; NHMUK PV R1239: part and counterpart that preserve impressions of the left hemimandible, gastralia, pectoral girdle, partial right forelimb, pelvic girdle and left hindlimb; NHMUK PV R1240: two blocks with caudal vertebrae that fits with NHMUK PV R1241; NHMUK PV R1241: hindlimb fragments; BRLSI M20a, b: two blocks with dorsal and caudal vertebrae, dorsal ribs, gastralia, partial pelvic girdle and right hindlimb; MANCH L7642: skull and cervical vertebrae; MANCH L7643: ribs; Keele University, unnumbered: skull and partial skeleton embedded within three blocks (unprepared) (modified from Benton, 1990).

Emended diagnosis. Small rhynchosaur that differs from other archosauromorphs in the following combination of features: laterally facing and sub-circular orbit with a raised and thickened border; anterior process of the jugal dorsoventrally narrow, being lower than the portion of maxilla located immediately below it; short and subtriangular posterior process of the jugal that does not reach the quadratojugal dorsal surface, resulting in an incomplete lower temporal bar; incipient anterior process of the quadratojugal; flat dorsal surface of the prefrontal; dorsal surface of the frontal with a deep, V-shaped depression on its posterior end; maxillary lateral tooth bearing area crest-shaped; posteromedially-to-anterolaterally oriented ridge on the posterior end of the palatal process of the pterygoid; posterior dorsal and sacral vertebrae with a deep fossa placed immediately lateral to the base of the neural spine; and second sacral rib bifurcated distally, with a tapering posterolateral process.

Remarks. Rhynchosaurus articeps was the first rhynchosaur genus and species to be erected (Owen, 1842), but it was not comprehensively described until the monographic work by Benton (1990). Rhynchosaurus articeps is currently the best-known Middle Triassic rhynchosaurid. Some reinterpretations of the anatomy of the species were recently made by Ezcurra, Montefeltro & Butler (2016), such as the presence of an open lower temporal bar and a distinctly bifurcated second sacral rib. This species has been frequently included as a representative of rhynchosaur anatomy in phylogenetic analyses focused on basal archosauromorphs (e.g., Dilkes, 1998; Gottmann-Quesada & Sander, 2009; Pritchard et al., 2015).

Bentonyx sidensis Langer et al., 2010a

Age. Late Anisian, Middle Triassic (Benton et al., 1994; Hounslow & McIntosh, 2003).

Locality. Pennington Point, 20 metres west of the Sid River outfall, Devon, southwest England, UK (Hone & Benton, 2008; Langer et al., 2010a).

Stratigraphic horizon. Otter Sandstone Formation (Hone & Benton, 2008; Langer et al., 2010a).

Holotype. BRSUG 27200: nearly complete skull, lacking the lower part and the posterolateral corners of the temporal areas, and partial mandible lacking most of the post-dentary bones (Langer et al., 2010a).

Diagnosis. Langer et al. (2010a: 1884) recognized two autapomorphies in their diagnosis of Bentonyx sidensis: a rounded depression on the ventral surface of the basisphenoid; and exceptionally large basal tubera. In addition, Langer et al. (2010a) listed the following features to distinguish Bentonyx sidensis from the likely sympatric species Fodonyx spenceri: narrower posterior margin of the skull (maximum width subequal to total skull length); a slender anterior process of the jugal (subequal in depth to the underlying portion of the maxilla); anterior margin of the quadrate process of the pterygoid forming an angle of less than 50°to the sagittal line; and maxillary tooth-bearing plates corresponding to more than half of the palatal length, measured from the anterior tip of the vomer to the posterior margin of the pterygoid (not including the posterior projection of the quadrate process).

Remarks. Hone & Benton (2008) described a new, fairly complete skull from the Otter Sandstone (BRSUG 27200) and referred it to Fodonyx spenceri. Subsequently, Langer et al. (2010a) revisited the taxonomy of the Devon rhynchosaur specimens and found strong evidence in support of a taxonomic distinction between the holotype of Fodonyx spenceri (EXEMS 60/1985.292) and the recently described skull (BRSUG 27200). The latter specimen was interpreted as the holotype of a new genus and species: Bentonyx sidensis. The holotype of Bentonyx sidensis represents one of the most exquisitely preserved Middle Triassic rhynchosaur skulls.

Eorasaurus olsoni Sennikov, 1997

Age. Late Capitanian–Wuchiapingian, midde–late Permian (Taylor et al., 2009; Ezcurra, Scheyer & Butler, 2014).

Locality. Right bank of the Volga River, village of Il’inskoe, Tetyushi District, European Russia (Sennikov, 1997).

Stratigraphic horizon. North Dvina Gorizont, Tarstan (Sennikov, 1997).

Holotype. PIN 156/109: two middle cervical vertebrae, one fairly complete and the second represented by the anterior half (Ezcurra, Scheyer & Butler, 2014).

Referred specimens. PIN 156/108: three posterior cervical vertebrae, the first of which is represented by the posterior end only; PIN 156/110: four partial anterior dorsal vertebrae and proximal portion of left anterior rib; PIN 156/111: two indeterminate long bones and some bone fragments (Ezcurra, Scheyer & Butler, 2014). The holotype and referred specimens are interpreted as belonging to the same individual (Sennikov, 1997; Ezcurra, Scheyer & Butler, 2014).

Emended diagnosis. Small archosauromorph that differs from other diapsids in the following combination of features (autapomorphies indicated with an asterisk): posterior cervical vertebrae with paradiapophyseal, posterior centrodiapophyseal and prezygodiapophyseal laminae; accessory, posterodorsally-to-anteroventrally oriented lamina partially subdividing the centrodiapophyseal fossa*; median keel on the ventral surface of the posterior cervical vertebrae; posterior cervical intercentra; long diapophysis in anterior dorsal vertebrae; and anterior dorsal rib with a thin lamina connecting the tuberculum and capitulum.

Remarks. Eorasaurus olsoni was originally erected and identified as a protorosaurid archosauromorph by Sennikov (1997). Although this species is one of the oldest known archosauromorphs, subsequent authors have ignored it. Ezcurra, Scheyer & Butler (2014) revisted the anatomy of Eorasaurus olsoni and reinterpreted some features, and included it for the first time in a quatitative phylogenetic analysis. Sennikov (1997) interpreted Eorasaurus olsoni as closely related to Protorosaurus speneri, but Ezcurra, Scheyer & Butler (2014) recovered this species as a possible member of Archosauriformes and Protorosaurus speneri as a basal archosauromorph. As a result, Eorasaurus olsoni is potentially the oldest known archosauriform (and also saurian) body fossil (Ezcurra, Scheyer & Butler, 2014; Bernardi et al., 2015).

Prolacertoides jimusarensis Young, 1973a

Age. Induan, Early Triassic (Young, 1973a; Lucas, 2010).

Locality. Dongxiaolongkou, Xinjiang Autonomous Region, China (Young, 1973a).

Stratigraphic horizon. Lower part of the Jiucaiyuan Formation, Cangfanggou Group (Young, 1973a).

Holotype. IVPP V3233: dorsoventrally compressed partial snout.

Emended diagnosis. Small archosauromorph that differs from other diapsids in the following combination of features: maxilla with a convex anterodorsal margin; 19 tooth positions in the maxilla; straight, conical and unserrated maxillary tooth crowns; well developed and subtriangular medial process on the prefrontal; and anterior processes of the pterygoids contact to each other extensively.

Remarks. Prolacertoides jimusarensis was briefly described by Young (1973a). The specimen is rather dorsoventrally compressed and, as a result, the lateral surfaces of the left maxilla and lacrimal face dorsolaterally (Fig. 7). Part of the possible left premaxilla is preserved in semiarticulation with the maxilla. Both maxillae, nasals, prefrontals, vomers, palatines, pterygoids, left ectopterygoid, partial right ectopterygoid, and probably the anterior ends of the jugals are preserved. The surfaces of the bones are generally well preserved, but some of them are severely damaged, such as the right maxilla and the anterior end of the left maxilla. The specimen is covered with glue and, as a consequence, sutures are usually difficult to discern.

Figure 7: Prolacertoides jimusarensis.
Holotype partial skull (IVPP V3233) in (A) dorsal; (B) ventral; (C) right lateral; and (D) left lateral views, and close up of right anterior maxillary tooth crowns. Numbers indicate character-states scored in the data matrix and the arrows indicate anterior direction. Abbreviations: bs, basisphenoid; ect, ectopterygoid; ju, jugal; la, lacrimal; lmtr, left maxillary tooth row; lprf, left prefrontal; mx, maxilla; na, nasal; pl-pt, palatine-pterygoid; rmtr, right maxillary tooth row; rprf, right prefrontal. Scale bars equal 5 mm, and 0.5 mm in the close up.

The snout is anteriorly tapering both in lateral and dorsal views. Indeed, the maxillae are strongly divergent from each other posteriorly, but this could be exaggerated by the post-mortem dorsoventral compression that the specimen has suffered. The posterior border of the external nares and the anterior half of the border of the orbit are preserved. An antorbital fenestra is absent. The anterior portion of the maxilla tapers anteriorly and its anterodorsal margin is slightly convex in lateral view, contrasting with the concave margin present in Jesairosaurus lehmani (ZAR 06) and some tanystropheids (e.g., Amotosaurus rotfeldensis: SMNS 90601; Tanystropheus longobardicus: Nosotti, 2007). As a result, it seems that the maxilla did not participate in the border of the external naris. The ascending process is anteroposteriorly broad and well developed dorsally, reaching the lateral margin of the skull roof. The suture with the lacrimal extends anterodorsally-to-posteroventrally and is posteriorly concave. It appears that the anterior process of the jugal overlaps laterally the posterior end of the maxilla, but this interpretation should be treated with caution. The anterior tip of the jugal apparently extended anteriorly beyond the level of the anterior border of the orbit, contrasting with the condition in several basal saurians (e.g., Jesairosaurus lehmani: ZAR 06; Gephyrosaurus bridensis: Evans, 1980). The maxillary tooth row finishes well anterior to the level of the anterior border of the orbit, contrasting with the more posteriorly extending tooth row present in other basal saurian (e.g., Gephyrosaurus bridensis: Evans, 1980; Protorosaurus speneri: Gottmann-Quesada & Sander, 2009; Jesairosaurus lehmani: ZAR 07; Macrocnemus bassanii: PIMUZ T4822). There are approximately 19 tooth positions based on the right maxilla, but the tooth count in the left maxilla cannot be determined because its posterior end is still covered with matrix. The maxillary tooth crowns are straight in labial view and lack denticles. In cross-section the anterior and middle maxillary crowns are circular and the posterior crowns are circular to slightly labiolingually compressed. The morphology of the teeth resembles that of Jesairosaurus lehmani (ZAR 06, 07), Amotosaurus rotfeldensis (SMNS 90601) and Youginia capensis (SAM-PK-K6205), but contrasts with the distally curved crowns of Macrocnemus bassanii (PIMUZ T4822) and Prolacerta broomi (BP/1/471, 4504a). Young (1973a) described and figured a middle maxillary tooth with a mesiodistal constriction at the base of the crown. Unfortunately, this tooth is now broken off and this feature could not be checked. Nevertheless, the first maxillary tooth crown is fairly complete and lacks a constriction at its base. There is no evidence of ankylosis between the teeth and the maxilla.

The anterior end of the nasals is damaged, but it seems that the posterior border of the external nares is preserved (cf. Young, 1973a). It seems that the external nares are marginal and extended posteriorly to the level of the suture between the premaxilla and maxilla. The external naris does not taper posterodorsally, contrasting with some basal lepidosauromorphs (e.g., Gephyrosaurus bridensis: Evans, 1980). The nasal is laterally expanded at its posterior end and possesses a long, anterolaterally oriented suture with the prefontal. By contrast, the suture between the prefrontal and nasal is mainly anteroposteriorly oriented in Prolacerta broomi (BP/1/471) and archosauriforms (e.g., Proterosuchus fergusi: BSPG 1934 VIII 514, RC 846, SAM-PK-K10603; Erythrosuchus africanus: BP/1/5207, NMQR 1473). The lacrimal is a slit-like, anterodorsally-to-posteroventrally oriented bone that resembles in morphology that of Prolacerta broomi (BP/1/471). There is no anterior process of the lacrimal and the bone possibly formed part of the anterior border of the orbit, but the latter condition cannot be determined confidently. The lacrimal is relatively anteroposteriorly broad and, as a result, the bone is well exposed on the lateral surface of the snout. The anterior process of the jugal seems to have been anteroposteriorly long and forms the ventral border of the orbit. The prefontals are widely exposed on the skull roof at level with the anterior border of the orbits, resembling the condition in Prolacerta broomi (Modesto & Sues, 2004). The prefrontal possesses a subtriangular medial projection that strongly constrictes transversely the suture between the nasals and frontals, as occurs in Trilophosaurus buettneri (Spielmann et al., 2008) and Gephyrosaurus bridensis (Evans, 1980). The dorsal surface of the prefrontal is smooth and transversely convex, lacking any change in slope between the dorsal and lateral surfaces of the bone. The prefrontal forms the anterodorsal border of the orbit, but the ventral process is not preserved on both sides and, as a result, it is not possible to determine how ventrally it extended. There is a circular, large foramen on the lateral surface of the prefrontal, immediately dorsal to the suture with the lacrimal and adjacent to the anterior border of the orbit. This foramen may represent the exit of the naso-lacrimal duct.

The pterygoids contact each other extensively at the median line, contrasting with the condition in Prolacerta broomi (Modesto & Sues, 2004) and basal archosauriforms (e.g., Proterosuchus fergusi: RC 59; Proterosuchus goweri: NM QR 880), in which there is an interpterygoid vacuity. It is not possible to discern the suture between vomers and pterygoids, nor between palatines and pterygoids. The choanae cannot be recognized, but they should have been placed anteriorly in the palate. The pterygoids-palatines are strongly expanded transversely and anteroposteriorly in the palate. The transverse process of the pterygoid possesses a posterolaterally oriented posterior margin. The left ectopterygoid is well preserved and was labelled as pterygoid by Young (1973a: Fig. 1). The ectopterygoid expands anteroposteriorly at its lateral end, acquiring a fan-shaped morphology in ventral view, closely resembling the morphology present in Gephyrosaurus bridensis (Evans, 1980). The ectopterygoid articulates laterally only with the jugal. It was not possible to recognize any palatal teeth in the pterygoids and palatines, but this could be a result of poor preservation. The quadrate process of the pterygoid is posterolaterally oriented and long, but the contact with the quadrate is not preserved or discernable. The suborbital fenestra is antroposteriorly very short, contrasting with the condition usually present in basal archosauriforms. Between the quadrate processes of the pterygoids there is a bone with a strongly concave ventral surface that likely represents the parasphenoid or parabasisphenoid (cf. Young, 1973a).

Prolacerta broomi Parrington, 1935

Age. Induan, earliest Triassic (Groenewald & Kitching, 1995).

Localities. Harrismith Commonage, Harrismith District, Free State, South Africa (type locality; Parrington, 1935). Referred specimens were collected from several localities in the Katberg Formation (Lystrosaurus AZ), South Africa (see Gow, 1975; Modesto & Sues, 2004).

Stratigraphic horizon. Katberg Formation, Lystrosaurus AZ, Tarkastad Subgroup, Beaufort Group, Karoo Supergroup, Karoo Basin (Parrington, 1935; Gow, 1975; Modesto & Sues, 2004). In addition, Colbert (1987) referred specimens from the Fremouw Formation (earliest Triassic) of the Transantarctic Mountains of Antarctica to Prolacerta broomi (see below).

Holotype. UMZC 2003.40: a partial skull and mandible.

Referred material. AMNH 9502: postcranial skeleton; BP/1/471: complete skull with attached mandible; BP/1/2675: nearly complete skull, now mostly disarticulated, with postcranial skeleton; BP/1/2676: nearly complete skeleton; BP/1/4504a: skull of a small individual; BP/1/5066: partial, flattened skull; BP/1/5375: skull, complete from mid-snout to occiput with partial mandible; GHG 431: partial skull and mandible, lacking the snout; SAM-PK-K10018: fairly complete, somewhat weathered skull and mandible; SAM-PK-K10797: well-preserved skull and posterior half of mandible attached to anterior cervical vertebrae; UCMP 37151: complete skull with articulated cervical vertebrae.

Emended diagnosis. Modesto & Sues (2004: 336) provided a diagnosis of Prolacerta broomi, which is modified here as follows. Prolacerta broomi is a basal archosauromorph distinguished from other saurians by the presence of: septomaxillae; notch on the ventral margin of the alveolar margin along the premaxilla–maxilla suture; conspicuous posterolateral exposure of the lacrimal duct openings; well developed posterolateral process on the frontal, resulting in an acute-angled and V-shaped suture between frontals and parietals; parietals lacking a sub-rectangular fossa on the posterior half of the dorsal surface of the bones; absence of postparietals; extensive contact between the surangular and the prearticular in the articular region of the lower jaw.

Remarks. Parrington (1935) named Prolacerta broomi and considered it as a thecodont intermediate between basal diapsids and lizards. Subsequently, Camp (1945) described a new specimen and interpreted it as the closest relative of the Permian Protorosaurus speneri, thus germinating the concept of a monophyletic “Protorosauria.” More specimens of Prolacerta broomi were collected from the Lystrosaurus AZ of South Africa during the subsequent 30 years and Gow (1975) provided for the first time a rather comprehensive description of the anatomy of the species. Colbert (1987) reported the presence of Prolacerta broomi from earliest Triassic beds of Antarctica, but these specimens are not considered for the scorings of the present analysis because a detailed, updated taxonomic revision of this material is needed. Modesto & Sues (2004) redescribed in detail the cranial anatomy of Prolacerta broomi based on both historical and recently collected specimens. Prolacerta broomi has been considered a key taxon in phylogenetic analyses, mainly to optimize the ancestral character-states of Archosauriformes. There is currently a general consensus that Prolacerta broomi represents the sister-taxon or one of the most closely related taxa of Archosauriformes (e.g., Dilkes, 1998; Modesto & Sues, 2004; Gottmann-Quesada & Sander, 2009; Nesbitt, 2011; Ezcurra, Scheyer & Butler, 2014; Pritchard et al., 2015), contrasting with early cladistics analyses that found this species as more closely related to Protorosaurus speneri and tanystropheids (e.g., Benton, 1985; Jalil, 1997) than to archosauriforms.

First-hand study of most available specimens of Prolacerta broomi allowed the reinterpretion of some anatomical features that do not agree with the skull reconstruction recently published by Nesbitt (2011). Since some of these features are of potential phylogenetic significance, they are discussed as follows. The anterior tip of the maxilla of the referred specimen of Prolacerta broomi BP/1/471 possesses an anteriorly opening notch, which is placed immediately below the articulation between the maxilla and the postnarial process of the premaxilla. This condition is very similar to that present in proterosuchids (e.g., RC 846) and is identified as an interruption of the alveolar margin of the skull at the level of the premaxilla–maxilla suture, which was not described or illustrated by previous authors (Gow, 1975; Modesto & Sues, 2004; Nesbitt, 2011). An interrupted alveolar margin between the premaxilla and maxilla is also preserved in the referred specimen of Prolacerta broomi BP/1/4504a. Nesbitt (2011: Fig. 16A) reconstructed the jugal of Prolacerta broomi as completely lacking a posterior process. However, this process was described and illustrated by previous authors (Gow, 1975; Modesto & Sues, 2004) and its presence is supported here based on multiple specimens (e.g., BP/1/2675, 5375; SAM-PK-K10797). The quadratojugal has been reconstructed by Gow (1975) as a slightly ventrally extended, splint-like bone that does not reach the distal end of the quadrate. However, the quadratojugal reaches and partially overlap the ventral end of the quadrate in lateral view, with a moderately posteriorly expanded ventral end, in at least one well-preserved referred specimen (SAM-PK-K10797). The retroarticular process of the lower jaw is strongly bowed dorsally, resembling the condition in Proterosuchus alexanderi (NMQR 1484), but contrasting with previous reconstructions (e.g., Gow, 1975; Nesbitt, 2011).

Kadimakara australiensis Bartholomai, 1979

Age. Induan, earliest Triassic (Warren & Hutchinson, 1990; Warren, Damiani & Yates, 2006).

Locality. 72 kilometres southwest of Rolleston, central Queensland, Australia (Bartholomai, 1979).

Stratigraphic horizon. Lower beds of the upper part of the Arcadia Formation, Rewan Group (Bartholomai, 1979).

Holotype. QMF 6710: temporal region of skull and right post-dentary bone of the lower jaw.

Referred material. QMF 6676: partial snout and anterior half of the lower jaw.

Emended diagnosis. Kadimakara australiensis is a basal archosauromorph distinguished from other saurians by the presence of (autapomorphy indicated with an asterisk): well developed posterolateral process on the frontal, resulting in an acute-angled and V-shaped suture between frontals and parietals; parietals with a sub-rectangular fossa on the posterior half of the dorsal surface of the bones*; and absence of postparietals. Although Bartholomai (1979: 226) included in his original diagnosis of the species the autapomorphy enumerated here for the species, an emended diagnosis was provided here because the putative postorbital and postfrontal described by Bartholomai (1979) are reinterpreted here as squamosal, and postorbital and postfrontal, respectively (see below).

Remarks. Bartholomai (1979) named the new genus and species Kadimakara australiensis and recognized its close similarities with the South African species Prolacerta broomi. Subsequent authors proposed that Kadimakara australiensis is possibly a subjective junior synonym of Prolacerta broomi (Borsuk-Białynicka & Evans, 2009; Evans & Jones, 2010). However, this hypothesis of synonymy is not followed here because Kadimakara australiensis possesses a median subrectangular fossa on the posterior half of the parietals that is separated from the margins of the supratemporal fossae by broad flat surfaces (QM F6710) (Fig. 8: mfo). This condition resembles in its position the pineal fossa of proterosuchids (e.g., Proterosuchus fergusi: TM 201, SAM-PK-K10603; Proterosuchus goweri: NMQR 880; Proterosuchus alexanderi: NMQR 1484) and some erythrosuchids (e.g., Erythrosuchus africanus: BP/1/5207, NHMUK PV R3592, NMQR 1473). By contrast, all studied specimens of Prolacerta broomi lack a fossa on the posterior half of the parietals or possesses a median fossa that is confluent with the margins of the supratemporal fossae (BP/1/471, 2675, 4504a, 5375; GHG 431; SAM-PK-K10797; UMCZ 2003.41R). As a result, the morphology of the dorsal surface of the parietals allows these closely related species to be distinguished from each other.

Figure 8: Kadimakara australiensis.
(A, B) Holotype postorbital region of skull (QMF 6710) and (C, D) referred snout (QMF 6676) in (A) dorsal; (B, C) right lateral; (D) and left lateral views. Numbers indicate character-states scored in the data matrix and the arrows indicate anterior direction. Abbreviations: apsq, anterior process of the squamosal; dt, dentary; fr, frontal; la, lacrimal; mfo, median fossa; mpsq, medial process of the squamosal; mx, maxilla; po, postorbital; pofr, postfrontal; ppsq, posterior process of the squamosal; qj, quadratojugal; sa, surangular; stf, supratemporal fenestra; stfo, supratemporal fossa; vpsq, ventral process of the squamosal. Scale bars equal 2 mm.

The first-hand study of the hypodigm of Kadimakara australiensis allowed the reinterpretion of some of the bones originally identified by Bartholomai (1979). This author described the postorbital as having a long, deep and anteriorly directed medial process and that the sutural relationship with the squamosal is difficult to interpret because it appears to be very close. The reinterpretion presented here is that the element identified by Bartholomai (1979) mainly as a postorbital is actually a squamosal and only the distal end of the ascending process of the postorbital is preserved (Fig. 8). The reinterpreted squamosal possesses a morphology that closely resembles that of Prolacerta broomi, with an anteroventrally oriented, straight and subrectangular ventral process that forms with the anterior process a squared posterodorsal corner of the infratemporal fenestra (QMF 6710). The preserved distal end of the ascending process of the postorbital is medially oriented and forms the anterior border of the supratemporal fenestra, excluding the postfrontal from the border of this opening.

The holotype of Kadimakara australiensis is based on the postorbital region of a skull (QMF 6710). A partial snout (QMF 6676) from the same locality was referred to the species, but with no clear association (Bartholomai, 1979). There are no overlapping bones between the specimens, and, as a result, their assignment to the same species is ambiguous. Nevertheless, the morphologies of both specimens are consistent with that of an animal similar to the non-archosauriform archosauromorph Prolacerta broomi. As such, the referral of QMF 6676 to Kadimakara australiensis can be considered a working hypothesis until there is more complete information that would allow it to be supported or rejected. Therefore, the holotype and complete hypodigm (holotype + referred specimen) of Kadimakara austaliensis were included as different terminals.

Boreopricea funerea Tatarinov, 1978

Age. Olenekian, late Early Triassic (Sennikov, 2008).

Occurrence. Core sample at 1,112.3 metres depth, Kolguyev Island, Arkhangel Province, Arctic Russia (Tatarinov, 1978; Benton & Allen, 1997).

Holotype. PIN 3708/1: nearly complete skull and postcranium, lacking the pelvis, posterior dorsal and anterior caudal vertebrae (Benton & Allen, 1997).

Referred material. PIN 3708/2: anterior end of the snout (Tatarinov, 1978). This specimen could not be located by Benton & Allen (1997).

Emended diagnosis. Benton & Allen (1997: 932) provided an emended diagnosis for Boreopricea funerea, which is modified here based on some anatomical reinterpretations of the specimen. Boreopricea funerea is a basal archosauromorph distinguished from other saurians by the presence of: jugal-squamosal contact; straight fronto-parietal suture; extremely reduced or absence of posterior process of jugal; more than seven cervical vertebrae; mammillary processes on the neural spines of cervico-dorsal vertebrae; metacarpal III equal in length to, or longer than, metacarpal IV; and second phalanx on pedal digit V is long compared to other phalanges.

Remarks. Tatarinov (1978) named the new Triassic genus and species Boreopricea funerea and considered that it was an intermediate form between Prolacerta broomi from South Africa and Macrocnemus bassanii from western Europe. The anatomy of the species was reviewed by Benton & Allen (1997) and they mentioned that the specimen had been considerably damaged since its original description. These authors agree in the general similarity between Boreopricea funerea and Prolacerta broomi. Benton & Allen (1997) included Boreopricea funerea in a quantitative phylogenetic analysis for the first time, which was focused almost exclusively in prolacertiforms, and recovered it as more closely related to tanystropheids than to Prolacerta broomi and Protorosaurus speneri. A very similar result was found independently by Jalil (1997). Boreopricea funerea was scored based on first-hand observations of the specimen and complemented with the publications of Tatarinov (1978) and Benton & Allen (1997). The interpretation of some anatomical features from the skull differs between both authors and cannot be evaluated due to the very bad current state of preservation of this anatomical region (PIN 3708/1). These characters were scored as missing data in the current data matrix.

Archosaurus rossicus Tatarinov, 1960

Age. Late Changhsingian, latest Permian (Rubidge, 2005; Sennikov & Golubev, 2006; Sennikov & Golubev, 2012; Benton, Tverdokhlebov & Surkov, 2004; Krassilov & Karasev, 2009).

Locality. Vyazniki locality, near Vyazniki, Vladamir Province, Russia (Tatarinov, 1960; Sennikov, 1988a).

Stratigraphic horizon. Uppermost part of the Tatarian series, “Vyazniki Biotic Assemblage” (Tatarinov, 1960; Sennikov, 1988a).

Holotype. PIN 1100/55: isolated left premaxilla lacking the distal portion of the prenarial and postnarial processes and teeth.

Putative referred material. PIN 1100/78: left dentary; PIN 1100/48: skull roof; PIN 1100/85: four tooth crowns; PIN 1100/66, 66a, 66b: three cervical vertebrae. Tatarinov (1960) and Sennikov (1988a) also referred other cranial and postcranial bones that are not included here among the putative referred material of the species because their morphology is not consistent with that of a proterosuchid (e.g., squamosal reinterpreted as an indeterminate bone by Ezcurra, Scheyer & Butler (2014)) or also resemble that of other archosauromorph lineages and lack archosauriform apomorphies (e.g., proximal end of tibia) (Ezcurra, Scheyer & Butler, 2014).

Emended diagnosis. Archosaurus rossicus is a proterosuchid distinguished from other diapsids on the basis of the following unique combination of characters-states: main axis of the palatal process of the premaxilla forming an angle of about 20°with respect to the main axis of the postnarial process, probably indicating the presence of a strongly downturned premaxilla; more than five tooth positions in the premaxilla; first four premaxillary alveoli open lateroventrally; and strongly acute angle formed between the anterior margin of the premaxillary body and the alveolar margin. The premaxilla of Archosaurus rossicus is extremely similar to that of Proterosuchus fergusi, Proterosuchus goweri and “Chasmatosaurusyuani, but it differs in the last feature listed in the diagnosis.

Remarks. Archosaurus rossicus is the oldest known unequivocal archosauriform (Tatarinov, 1960; Charig & Reig, 1970; Charig & Sues, 1976; Sennikov, 1988a; Gower & Sennikov, 2000; Nesbitt, 2011; Ezcurra, Butler & Gower, 2013; Ezcurra, Scheyer & Butler, 2014), but it has been included only recently in quantitative phylogenetic analyses (Nesbitt, 2011; Ezcurra, Scheyer & Butler, 2014). These analyses recovered Archosaurus rossicus as a proterosuchid, as proposed by previous authors. Nesbitt (2011) and Ezcurra, Scheyer & Butler (2014) discussed the assignment of the specimens previously referred to Archosaurus rossicus and considered these referrals problematic because of the lack of overlapping characters with the holotype and the fact that the specimens come from different stratigraphic levels within a geographically large locality with a stratigraphic thickness of around 25 metres (Ezcurra, Scheyer & Butler, 2014). As a result, Nesbitt (2011) and Ezcurra, Scheyer & Butler (2014) restricted the scorings of Archosaurus rossicus to its holotype premaxilla, and this decision is also followed here. The hypodigm of Archosaurus rossicus was described by Tatarinov (1960) and Sennikov (1988a), and the anatomical knowledge of the holotype was recently complemented by Ezcurra, Scheyer & Butler (2014).

Holotype of Proterosuchus fergusi

Age. Induan, earliest Triassic (Rubidge, 2005; Lucas, 2010).

Locality. Farm Wheatlands, Tarkastad, Chris Hani District, Eastern Cape Province, South Africa (Broom, 1903a).

Stratigraphic horizon. Upper Balfour Formation or lower Katberg Formation, Lystrosaurus AZ, Beaufort Group, Karoo Supergroup (Broom, 1903a).

Holotype. SAM-PK-591: partial, poorly preserved skull and lower jaw (Broom, 1903a; Welman, 1998; Ezcurra & Butler, 2015a).

Remarks. Proterosuchus fergusi has a long and conflicting taxonomic history that has been recently summarized by Ezcurra & Butler (2015a). Broom (1903a) erected this genus and species on the basis of the first proterosuchid specimen collected from the Early Triassic of South Africa: a poorly preserved partial skull and lower jaw (SAM-PK-591) that was diagnostic at that time. Subsequently, Hughes (1963) considered Proterosuchus fergusi an invalid archosauriform species, but this interpretation was not followed by subsequent authors (e.g., Hoffman, 1965; Charig & Reig, 1970; Cruickshank, 1972; Charig & Sues, 1976; Welman, 1998). Welman (1998) considered that all the proterosuchid species described at that time from the Lystrosaurus AZ of South Africa were subjective junior synonyms of Proterosuchus fergusi and proposed a revised diagnosis for the genus and species. However, Ezcurra & Butler (2015a) revised the taxonomy of the proterosuchid specimens from South Africa, in which they redescribed in detail the holotype of Proterosuchus fergusi and argued that it cannot be distinguished from other proterosuchids (e.g., “Chasmatosaurusyuani from China). As a result, following the recommendations of the International Code of Zoological Nomenclature, Ezcurra & Butler (2015a) proposed a neotype (RC 846) for Proterosuchus fergusi. The South African proterosuchid species “Chasmatosaurus vanhoepeni” and “Elaphrosuchus rubidgei” were considered junior synonyms of Proterosuchus fergusi by Ezcurra & Butler (2015a). I decided here to score the holotype of Proterosuchus fergusi alone in order to test if the specimen represents a member of Proterosuchidae.

Proterosuchus fergusi Broom, 1903a

Age. Induan, earliest Triassic (Rubidge, 2005; Lucas, 2010).

Localities. Farm Ruygte Valley 321, Middelburg, Chris Hani District, Eastern Cape Province, South Africa (neotype locality). Referred specimens have been collected in multiple localities from the same horizon as the neotype locality in South Africa (see Ezcurra & Butler, 2015a: Table 3).

Stratigraphic horizon. Upper Balfour Formation and/or lower Katberg Formation, Lystrosaurus AZ, Beaufort Group, Karoo Supergroup (see Ezcurra & Butler (2015a) and references herein).

Proposed neotype. RC 846 (mistakenly referred to as RC 96 by Welman & Flemming (1993) and subsequent authors), large fairly complete skull and lower jaw, atlas, axis, partial third cervical vertebra and first three cervical ribs.

Referred material. BP/1/3993: medium-sized (38.8 cm total skull length) partial skull and lower jaw (lacking right temporal region and the posterior ends of the mandibular rami), axis and five anterior–middle postaxial cervical vertebrae; BP/1/4016: small (c. 24 cm total skull length) partial skull and lower jaw (lacking the anterior ends of the premaxillae and the anterior half of skull roof), first four cervical vertebrae and probable atlantal rib and postaxial cervical ribs; BP/1/4224: small (c. 23 cm total skull length) posterior half of skull and lower jaw, axis and one cervical rib; BSPG 1934 VIII 514: large (43.5 cm total skull length) partial skull and complete lower jaw, first four cervical vertebrae with their ribs and intercentra; GHG 231: large (47.7 cm total skull length) partial skull (lacking the left maxilla) and complete lower jaw, first seven cervical vertebrae, and atlantal, axial, fourth and fifth cervical ribs; GHG 363: large partial snout, three cervicodorsal vertebrae with two right ribs in partial articulation, two middle dorsal vertebrae, one middle caudal vertebra, one posterior caudal vertebra, and interclavicle; RC 59 (holotype of “Elaphrosuchus rubidgei”): small (17.8 cm total skull length) partial skull and lower jaw (lacking prefrontals, lacrimals, left squamosal and quadratojugal, epipterygoids and braincase), an atlantal neural arch and some cervical ribs; SAM-PK-11208: medium-sized (35.0 cm total skull length) partial skull and lower jaw (lacking most of the skull roof and with the left side severely damaged), axis, third and fourth cervical vertebrae in articulation, probable fifth cervical to first dorsal vertebrae in articulation, three anterior dorsal vertebrae in articulation, possible first sacral vertebra and some long bone fragments; SAM-PK-K140: small (28.7 cm total skull length) partial skull (lacking the skull roof and braincase) and lower jaw, first four cervical vertebrae in articulation, a series of seven middle cervical to anterior dorsal vertebrae, two middle dorsal vertebrae, sacral vertebrae (now lost), several cervical and dorsal ribs and gastralia, right scapula (now lost), left ulna, radius, carpus and hand, partial pelvic girdle (currently lost), partial hindlimbs, including well-preserved left femur, right astragalus and calcaneum, and left foot in articulation and a bone previously identified as an isolated osteoderm (now only preserved as a mould); SAM-PK-K10603: large (c. 41 cm total skull length) fairly complete skull and lower jaw (missing most of the premaxillae) and atlas; and TM 201 (holotype of “Chasmatosaurus vanhoepeni”): large (c. 44 cm total skull length) partial skull and lower jaws. Botha-Brink, Huttenlocker & Modesto (2014: 300) briefly reported, but not figured, a new specimen (NMQR 3924) that was assigned to Proterosuchus fergusi on the basis of ‘the skull roof and tooth morphology’. This specimen was not discussed by Ezcurra & Butler (2015a) and in this contribution because it was not examined by the author.

Diagnosis. Proterosuchid archosauriform (skull length reaching up to approximately 50 cm and total body length up to 3–3.5 m) distinguished from other archosauromorphs on the basis of the following unique combination of character-states: premaxilla lacking a groove on the lateral surface of the main body; ratio of total length of maxilla versus length of maxilla anterior to the antorbital fenestra greater than 2.5; maxilla lacks an anterolaterally opening longitudinal groove adjacent to the anterior margin of the bone; minimum height of the horizontal process of maxilla is equal to or less than 13% of the total length of the maxilla; maxillary alveolar margin straight to gently convex in lateral view; quadrate with an angle between the posterior margins of the dorsal and ventral ends of less than 130°; presacral vertebrae with mammillary processes on the neural spines of at least cervicals 6 and 7 and absent on dorsals 4–7; and presence of postaxial intercentra (Ezcurra & Butler, 2015a: 164).

Remarks. See comments for the holotype of Proterosuchus fergusi. Different specimens currently referred to Proterosuchus fergusi have been described by several authors (e.g., Broom, 1903a; Broom, 1932; Broom, 1946; Haughton, 1924; Broili & Schröder, 1934; Gow, 1975) and the most comprehensive anatomical description of the species was conducted by Cruickshank (1972) and complemented by Welman (1998), Ezcurra & Butler (2015a) and Ezcurra & Butler (2015b). Nevertheless, a detailed and complete osteological description of the species is still unavailable and now in preparation by the author.

Proterosuchus goweri Ezcurra & Butler, 2015a

Age. Induan, earliest Triassic (Rubidge, 2005; Lucas, 2010).

Locality. Farm Kruisvlei (Kruisvlei 1095 in Brink (1955) and Kruisvlei 279 in Welman (1998)), east of Winburg, Lejweleputswa District, Free State Province, South Africa (Brink, 1955).

Stratigraphic horizon. Upper Balfour Formation or lower Katberg Formation, Lystrosaurus AZ, Beaufort Group, Karoo Supergroup (Brink, 1955).

Holotype. NMQR 880: partial skull with detached braincase, a right dorsal rib, and left tibia and fibula.

Diagnosis. Proterosuchid archosauriform (skull length of the only known individual c. 39 cm and total body length estimated in 2.5–3 m) distinguished from other archosauromorphs by the following combination of character-states (autapomorphies marked with an asterisk): premaxilla lacking grooves on the lateral surface; ratio of total length of maxilla versus length of maxilla anterior to the antorbital fenestra greater than 2.5; maxilla with an edentulous anterior end, the length of which is equivalent to that of two tooth positions; maxilla lacking an anterolaterally opening longitudinal groove adjacent to the anterior margin; minimum height of the horizontal process of maxilla is equal to or greater than 15% of the total length of the maxilla*; maxillary alveolar margin distinctly sigmoid in lateral or medial views, with a concave anterior two-thirds and a convex posterior third*; and quadrate with an angle between the posterior margins of the dorsal and ventral ends greater than 145°(Ezcurra & Butler, 2015a: 166, 167).

Remarks. Brink (1955) reported a new proterosuchid specimen (NMQR 880) from the Lystrosaurus AZ of South Africa that he assigned to “Chasmatosaurus vanhoepeni”. Welman (1998) considered all the proterosuchid specimens from South Africa referable to Proterosuchus fergusi, including NMQR 880. Ezcurra & Butler (2015a) noted that NMQR 880 possesses a unique combination of features that distinguish it from other archosauromorphs and used this specimen to erect the new species Proterosuchus goweri. The holotype of Proterosuchus goweri was briefly described by Brink (1955), and recently some anatomical comments were added by Ezcurra & Butler (2015a). A detailed description of the species is currently in preparation by the author.

Proterosuchus alexanderi (Hoffman, 1965)

Age. Induan, earliest Triassic (Rubidge, 2005; Lucas, 2010).

Locality. Farm Zeekoegat, four miles from Venterstad, Joe Gqabi District, Eastern Cape Province, South Africa (Hoffman, 1965).

Stratigraphic horizon. Upper Balfour Formation or lower Katberg Formation, Lystrosaurus AZ, Beaufort Group, Karoo Supergroup (Hoffman, 1965).

Holotype. NMQR 1484: small, fairly complete skull (lacking most of the premaxillae) and postcranial axial skeleton (lacking the posterior half of the caudal series) and partial appendicular skeleton.

Diagnosis. Proterosuchid archosauriform distinguished from other archosauromorphs by the following combination of character-states (autapomorphies marked with an asterisk): ratio of total length of maxilla versus length of maxilla anterior to the antorbital fenestra less than 2.3*; minimum height of the horizontal process of maxilla is equal to or less than 13% of the total length of the maxilla; maxillary alveolar margin straight to gently convex in lateral view; frontals with a dorsal surface ornamented by a series of anastomosed shallow grooves and subcircular pits with a seemingly random arrangement* (Ezcurra & Butler, 2015a: Figs. 4A and 4B); quadrate with an angle between the posterior margins of the dorsal and ventral ends greater than 145 degree; presacral vertebrae with mammillary processes on the neural spines present in presacrals 14–16 (dorsals 5–7)*; (7) presence of postaxial intercentra; and first sacral rib distally subdivided* (Ezcurra & Butler, 2015a: 166).

Remarks.Chasmatosaurusalexanderi was erected by Hoffman (1965) on the basis of a specimen that represents the most complete proterosuchid skeleton collected so far from the Lystrosaurus AZ of South Africa. This species was considered a subjective junior synonym of “Chasmatosaurus vanhoepeni” by later authors (e.g., Charig & Reig, 1970; Cruickshank, 1972; Charig & Sues, 1976; Welman, 1998), but Ezcurra & Butler (2015a) resurrected the species because it possessed a unique combination of character-states and autapomorphies that distinguish it from other proterosuchids. Since “Chasmatosaurus vanhoepeni” was considered a subjective junior synonym of Proterosuchus fergusi by Ezcurra & Butler (2015a), these authors tranfered “Chasmatosaurusalexanderi to the genus Proterosuchus, resulting in the new combination Proterosuchus alexanderi. The holotype of Proterosuchus alexanderi was originally briefly described by Hoffman (1965) and described more in detail by Cruickshank (1972). Clark et al. (1993), Welman (1998), Klembara & Welman (2009) and Ezcurra & Butler (2015a) provided additional anatomical observations.

Chasmatosaurusyuani Young, 1936

Age. Induan, earliest Triassic (Rubidge, 2005; Lucas, 2010).

Localities. Shoukou Fukanghsien, Fuyuan County, Heilongjiang Province, People’s Republic of China (type locality). Referred specimens come from Hungshantig, Hotung, Heilongjiang Province, People’s Republic of China, and the same stratigraphic horizon as the holotype (Young, 1936; Young, 1963).

Stratigraphic horizon. Jiucaiyuan Formation, Lystrosaurus AZ (Young, 1936; Young, 1963).

Holotype. IVPP V36315: fragmentary skeleton composed of a partial snout and postcranium. The postcranium included axial and appendicular bones (see Young, 1936), but they could not be located in the collection of the IVPP (May 2013) and should be considered currently lost.

Referred material. IVPP V2719: partial braincase and postcranium, including elements of the axial series, pectoral girdle, forelimb, pelvic girdle and hindlimb; IVPP V4067: fairly complete articulated skeleton, missing the distal two-thirds of the tail, gastralia, right hand and left himdlimb stilopodium and autopodium.

Emended diagnosis.Chasmatosaurusyuani is a medium-sized basal archosauriform that differs from other basal archosauromorphs by the following combination of features (autapomorphies indicated with an asterisk): lateral surface of the premaxillary body with a pair of grooves originated dorsally from a circular neurovascular foramen situated on the anterior half of the premaxillary body*; anterior process of the maxilla with a distinct shelf extending posterodorsally from the anteroventral tip of the bone and restricted to the anterior third of the process*; and anterior tip of the maxilla edentulous and slightly ventrally oriented.

Remarks. See Nesbitt et al. (2015).

Chasmatosaurus ultimusYoung, 1964 nomen dubium

Age. Anisian, early Middle Triassic (Liu, Li & Li, 2013).

Locality. Louzeyu Village, Wuhsiang County, Shanxi Province, People’s Republic of China (Young, 1958; Liu et al., 2015).

Stratigraphic horizon. Upper member of the Ermaying Formation (Young, 1958; Liu et al., 2015).

Holotype. IVPP V2301: incomplete anterior part of skull with lower jaw.

Remarks. IVPP V2301was originally described by Young (1958) as a referred specimen of “Chasmatosaurusyuani, but subsequently Young (1964) erected the new species “Chasmatosaurus ultimus” on the basis on this specimen. This species has been considered the youngest known member of Proterosuchidae until recently (Ezcurra, Butler & Gower, 2013). The original diagnosis of “Chasmatosaurus ultimus” differentiated this species from “Chasmatosaurusyuani on the basis of its smaller size and larger, more strongly recurved tooth crowns (Young, 1964). Liu et al. (2015) revised the specimen and concluded that it represents an indeterminate archosaur and the species is a nomen dubium. Although this species is invalid, it was included in the taxonomic sample of the present phylogenetic analysis to test the hypothesis that “Chasmatosaurus ultimus” is an archosaur, which was proposed by Liu et al. (2015) based on qualitative grounds.

Ankistrodon indicusHuxley, 1865 nomen dubium

Age. Induan, earliest Triassic (Rubidge, 2005; Lucas, 2010).

Locality. Deoli locality, close to Deoli village, West Bengal Province, India (Blanford in Huxley, 1865).

Stratigraphic horizon. Panchet Formation, Damodar Basin (Blanford in Huxley, 1865).

Holotype. GSI 2259: portion of distal end of horizontal process of the right maxilla with two teeth.

Remarks. The holotype of “Ankistrodon indicus” is based on an isolated maxillary fragment with two teeth. This species was the first proterosuchid taxon to be named (Huxley, 1865). Subsequently, Huene (1942) transferred “Ankistrodon indicus” to the genus “Chasmatosaurus” and referred to this species several vertebrae previously assigned to the dicynodont Dicynodon orientalis by Huxley (1865). Charig & Reig (1970) considered the holotype of “Ankistrodon indicus” indeterminate and, as a result, the genus and species should be regarded as nomina dubia, as previously proposed by Gower (1994). I agree with the conclusion of Charig & Reig (1970) after a first-hand study of the holotype, but the species was included in the taxonomic sampling of the present phylogenetic analysis in order to test its supposed proterosuchid affinities.

Tasmaniosaurus triassicus Camp & Banks, 1978

Age. Induan–early Olenekian, Early Triassic (Ezcurra, 2014).

Locality. Crisp and Gunn’s Quarry at the head of Arthur Street (42°52′50.0″S 147°18′10.6″E±100 metres), Hobart, Tasmania, Australia (Thulborn, 1986; Ezcurra, 2014).

Stratigraphic horizon. Upper levels of the Poets Road Siltstone Member, Knocklofty Formation, Upper Parmeener Supergroup, Tasmania Basin (Thulborn, 1986; Ezcurra, 2014).

Holotype. UTGD 54655: partial skeleton, mostly disarticulated, composed of right premaxilla; left maxilla; probable right maxilla; right lacrimal; both frontals, postfrontals and parietals; interparietal; ?supraoccipital; right pterygoid; ?epipterygoid; both dentaries; left splenial; one cervico-dorsal and one anterior or middle dorsal vertebra; fourteen to sixteen caudal vertebrae; several ribs, gastralia and haemal arches; interclavicle; ?femur; both tibiae; and multiple metatarsals and pedal phalanges (Ezcurra, 2014).

Supposed referred material. Some bone fragments from other localities in Tasmania were previously referred to Tasmaniosaurus triassicus (Warren, 1972; Forsyth et al., 1974) but could not be located in the collection of the UTGD in August of 2012. Thulborn (1986) considered these bones indeterminate.

Diagnosis. Tasmaniosaurus triassicus is a small-sized basal archosauromorph distinguished from other members of the clade by the following unique combination of character-states: premaxilla with posterodorsally oriented posterior process and ankylothecodont tooth implantation; maxilla with anteroposteriorly short anterior process; frontal with almost straight lateral margin; pterygoid with medial row of palatal teeth; dorsal vertebrae with paradiapophyseal and prezygodiapophyseal laminae and without distinct distal expansion of the neural spine; probable absence of osteoderms; and interclavicle with a diamond-shaped anterior end and a gracile and slightly transversely expanded posterior process (Ezcurra, 2014: 5).

Remarks. Camp & Banks (1978) named the proterosuchid species Tasmaniosaurus triassicus, which was redescribed by Thulborn (1986). This species was barely cited in the scientific literature during the subsequent 20 years (Ezcurra, Butler & Gower, 2013), until it was redescribed and figured in detail by Ezcurra (2014). Tasmaniosaurus triassicus has not been included in any quantitative phylogenetic analysis.

Exilisuchus tubercularisOchev, 1979nomen dubium

Age. Early Olenekian, Early Triassic (Gower & Sennikov, 2000).

Locality. Kzyl-Sai III 2 locality, Akbulak district, Orenburg Province, Russia (Ochev, 1979; Gower & Sennikov, 2000).

Stratigraphic horizon. Sludkian Gorizont, Vetlugian Supergorizont (Ochev, 1979; Gower & Sennikov, 2000).

Holotype. PIN 4171/25: partial left ilium.

Remarks.Exilisuchus tubercularis” was named by Ochev (1979) and interpreted as a possible proterosuchian. Sennikov (1995b) concluded that the systematic position of the species is very problematic, but it might represent a proterosuchid archosauriform. Gower & Sennikov (2000) and Ezcurra, Butler & Gower (2013) listed “Exilisuchus tubercularis” as a possible proterosuchid species. The isolated ilium lacks part of the preacetabular process, dorsal margin of the iliac blade and most of the postacetabular process (PIN 4171/25) (Fig. 9). The base of the preacetabular process possesses a tuberosity that does not reach the supraacetabular crest, resembling the condition in tanystropheids (e.g., Macrocnemus bassanii: Rieppel, 1989a; Tanystropheus longobardicus: Nosotti, 2007) and some dinosauriforms (e.g., Silesaurus opolensis: Dzik, 2003; Saturnalia tupiniquim: Langer, 2003). By contrast, this tuberosity is absent in early archosauriforms (e.g., Proterosuchus alexanderi: NMQR 1484; “Chasmatosaurusyuani: IVPP V2719; Erythrosuchus africanus: NHMUK PV R3592). An anteroposteriorly concave depression is placed immediately posterior to the tuberosity of the preacetabular process. The supraacetabular crest is poorly laterally developed. The medial surface of the ilium possesses two distinct facets for articulation with the sacral ribs. The ventral margin of the acetabular wall is damaged, but ventrally convex as preserved.

Figure 9: Exilisuchus tubercularis.”
Holotype partial left ilium (PIN 4171/25) in (A) lateral; (B) medial; and (C) dorsal views. Numbers indicate character-states scored in the data matrix and the arrows indicate anterior direction. Abbreviations: acw, acetabular wall; f.S1–2, facet for articulation with the first and second sacral ribs, respectively; isp, ischial peduncle; prap, preacetabular process; poap, postacetabular process; pup, pubic peduncle. Scale bar equals 2 mm.

The morphology of the holotype of “Exilisuchus tubercularis” differs from that present in proterosuchids and other archosauriforms but closely resembles that of tanystropheid archosauromorphs. Indeed, PIN 4171/25 cannot be distinguished from the ilia of Tanystropheus longobardicus and Macrocnemus bassanii and, as a result, “Exilisuchus tubercularis” is considered a nomen dubium, as previously proposed by Gower (1994). This species is included within the taxonomic sample of the current analysis in order to test quantitatively the phylogenetic position of the specimen.

Blomosuchus georgii” (Sennikov, 1992) nomen dubium

Age. Induan, earliest Triassic (Sennikov, 1992).

Locality. Spasskoe I locality, Vetluga River, Nizhnii Novgorod Province, Russia (Sennikov, 1992).

Stratigraphic horizon. Vokhmian Gorizont (Sennikov, 1992).

Holotype. PIN 1025/348: partial parabasisphenoid.

Putative referred material. PIN 1025/14: partial parabasisphenoid.

Remarks. Two putative proterosuchid species have been named from the same locality (Spasskoe I) of the Early Triassic Vokhmian Gorizont of Russia: “Blomosuchus gregorii” and Vonhuenia friedrichi (Sennikov, 1992). Sennikov (1992) named “Blomosuchus georgii” on the basis of an isolated partial parabasisphenoid that lacks most of the cultriform process and part of the intertuberal plate and the dorsolateral surface of the bone (PIN 1025/348) (Fig. 10A). Subsequently, Sennikov (1995b) referred to “Blomosuchus georgii” some isolated postcranial bones from the same locality. The holotype of Vonhuenia friedrichi is an isolated posterior cervical vertebra (PIN 1025/11) (Figs. 10D10F). An isolated parabasisphenoid, some vertebrae and other fragmentary postcranial bones collected in the type locality were referred to Vonhuenia friedrichi (Sennikov, 1992; Sennikov, 1995b) (Figs. 10B and 10G10I).

Figure 10: Blomosuchus georgii” and Vonhuenia friedrichi.
(A) holotype (PIN 1025/348) and (B) referred (PIN 1025/14) partial parabasisphenoids of “Blomosuchus georgii”; (C) parabasisphenoid of Proterosuchus alexanderi (NMQR 1484); and (D–F) holotype (PIN 1025/11) and (G–I) referred (PIN 1025/419, mirrored) cervico-dorsal vertebrae of Vonhuenia friedrichi in (A–C, F, I) ventral; (D) left lateral; (E, H) anterior; and right lateral (G) views. Numbers indicate character-states scored in the data matrix and the arrows indicate anterior direction. Abbreviations: af, accessory facet; btpbs, basal tubera of the parabasisphenoid; clp, clinoid process; cup, cultriform process; di, diapophysis; fo, foramina; pa, parapophysis; prz, prezygapophysis; vk, ventral keel. Scale bars equal 2 mm in (A, B, D–I) and 4 mm in (C).

The isolated partial parabasisphenoid (PIN 1025/14) referred to Vonhuenia friedrichi was distinguished from the holotype of “Blomosuchus gregorii” (PIN 1025/348) because of the presence of a proportionally longer parabasisphenoid body and differences in the shape of the basipterygoid processes (A Sennikov, pers. comm., 2013). However, the breakage of the median region of the intertuberal plate gives the artificial appearance that the body of the parabasisphenoid is anteroposteriorly shorter along the median line in the holotype of “Blomosuchus georgii” than it is in PIN 1025/14 (Figs. 10A and 10B). The right basipterygoid process of PIN 1025/14 is completely missing and only the base of the left process is preserved, with the latter having a strongly weathered surface. The position of the base of the basipterygoid process is identical in the holotype of “Blomosuchus georgii” and PIN 1025/14, and the orientation and shape of the distal articular surface of the basipterygoid process cannot be determined in PIN 1025/14. Accordingly, no substantial difference is recognised here between the holotype of “Blomosuchus georgii” and PIN 1025/14. As a result, both specimens probably belong to the same species, and a redescription and comparisons of these specimens with other early archosauriforms are provided as follows.

The parabasisphenoid of “Blomosuchus georgii” is horizontal in lateral view, constrasting with the posterodorsally-to-anteroventrally oriented braincases of Sarmatosuchus and erythrosuchids (Gower & Sennikov, 1996; Gower & Sennikov, 1997). The ventral surface of the basal tubera is strongly transversely convex and its lateral surface possesses a semilunar depression. This depression is slightly more anteriorly placed than that of Sarmatosuchus otschevi (Gower & Sennikov, 1997), but resembles the position present in Proterosuchus fergusi (NMQR 880) and Fugusuchus hejiapensis (Gower & Sennikov, 1996). The dorsal surface of the basal tubera is strongly transversely concave, and should have received the basioccipital contribution of the basal tubera and probably formed the floor of the unossified passage of the pseudolagenar recess. The intertuberal plate is developed as a posteriorly projected and curved shelf, which is completely preserved in the referred specimen (PIN 1025/14). The ventral surface of the parabasisphenoid possesses a shallow depression immediately anterior to the intertuberal plate. The foramina for the exit of the internal carotid arteries are placed posteromedially to the base of the basipterygoid processes, on the ventral surface of the braincase. These foramina are oval, with an anteromedially-to-posterolaterally oriented main axis. Well developed parasphenoid crests on the ventral surface of the parabasisphenoid originate posterior to the foramina for the passage of the internal carotids, curve anteriorly and run parallel to each other between the bases of the basipterygoid process and onto the base of the cultriform process. The morphology of the parasphenoid crests of “Blomosuchus georgii” is identical to that present in Prolacerta broomi (BP/1/2675), Proterosuchus alexanderi (NMQR 1484), Proterosuchus goweri (NMQR 880) and Fugusuchus hejiapensis (Gower & Sennikov, 1996). The parasphenoid crest is thicker on the cultriform process than more posteriorly. The basipterygoid processes are posteroventrally oriented in lateral view, as occurs in Proterosuchus alexanderi (NMQR 1484), Proterosuchus goweri (NMQR 880) and Fugusuchus hejiapensis (Gower & Sennikov, 1996). The groove for the palatine ramus of the facial nerve is very deep on the lateral surface of the bone and anteriorly defined by the clinoid process.

These comparisons between the holotype and probably referred parabasisphenoid of “Blomosuchus georgii” and other basal archosauriforms indicate that this species cannot be distinguished from the parabasisphenoids of other closely related species, such as Proterosuchus fergusi (BP/1/3993), Proterosuchus alexanderi (NMQR 1484), Proterosuchus goweri (NMQR 880) and Fugusuchus hejiapanensis (Gower & Sennikov, 1996). Therefore,“Blomosuchus” and “Blomosuchus georgii” are considered here as nomina dubia, as previously proposed by Gower (1994). Nevertheless, this species is included in the taxonomic sampling of the analysis to test quantitatively the phylogenetic affinities of the species for the first time and the presence of proterosuchids in the Lower Triassic beds of Russia. The lack of anatomical overlap between the postcranial bones previously referred to “Blomosuchus georgii” and the holotype, combined with the presence of another nominal species of putative proterosuchid (Vonhuenia friedrichi) at the same locality and horizon, suggests that caution is warranted in the taxonomic assignment of these specimens. As a result, the hypodigm of “Blomosuchus georgii” is restricted to and scored here based on the holotype (PIN 1025/348) and the parabasisphenoid PIN 1025/14 (previously referred to Vonhuenia friedrichi).

Vonhuenia friedrichi Sennikov, 1992

Age. Induan, earliest Triassic (Sennikov, 1992).

Locality. Spasskoe I locality, Vetluga River, Nizhnii Novgorod Province, Russia (Sennikov, 1992).

Stratigraphic horizon. Vokhmian Gorizont (Sennikov, 1992).

Holotype. PIN 1025/11: posterior cervical vertebra.

Referred material. PIN 1025/419: anterior portion of a posterior cervical vertebra.

Emended diagnosis. Vonhuenia friedrichi is a small-sized basal archosauromorph differentiated from the cervico-dorsal vertebrae of other members of the clade by the following unique combination of character-states: median keel on the ventral surface of the centrum; prezygodiapophyseal and postzygodiapophyseal laminae on the neural arch; accessory rib facet; and absence of mammillary processes on the neural spine.

Remarks. Sennikov (1992) erected the new genus and species Vonhuenia friedrichi on the basis of an isolated posterior cervical vertebra with three rib facets (Figs. 10D10F) and referred to the species several fragmentary postcranial, isolated bones. Sennikov (1995b) referred additional isolated specimens from the type locality to this species. As was the case for “Blomosuchus georgii”, there is no direct overlap between the isolated posterior cervical vertebra that represents the holotype of Vonhuenia friedrichi (PIN 1025/11) and the specimens referred to this taxon, with the probable exception of a single vertebra that also possesses a third rib articular facet (PIN 1025/419) (Figs. 10G10I). This condition is not present among the other referred vertebral specimens, which have only two articular facets for the ribs. This suggests that the other referred vertebrae are from different positions in the vertebral column than the holotype and PIN 1025/419. The latter specimen shares with the holotype (PIN 1025/11) the presence of prezygodiapophyseal and postzygodiapophyseal laminae, as well as a median longitudinal keel on the ventral surface of the centrum. This combination of features is not present in the cervico-dorsal vertebrae of other basal archosauromorphs and thus is diagnostic for Vonhuenia friedrichi and, as a result, the genus and species seems to be valid (contra Gower, 1994). The other previously referred vertebrae do not possess this combination of features, although it may be because they are from a different region of the vertebral column than PIN 1025/11 and PIN 1025/419. As a result, the hypodigm of Vonhuenia friedrichi is restricted here to the holotype (PIN 1025/11) and a referred cervico-dorsal vertebra (PIN 1025/419).

Chasmatosuchus rossicus Huene, 1940 (=“Tsylmosuchus samarensisSennikov, 1990)

Age. Early Olenekian, Early Triassic (Gower & Sennikov, 2000).

Locality. Vakhnevo locality, southern Cis-Urals, Vologda Oblast, Russia (Huene, 1940; Gower & Sennikov, 2000).

Stratigraphic horizon. Rybinskian Gorizont (Huene, 1940; Gower & Sennikov, 2000).

Lectotype. PIN 2252/381: two articulated posterior cervical vertebrae (ca. Cvs. 8–9) and their two respective intercentra.

Referred material. PIN 3200/217, 2424/6 (holotype of “Tsylmosuchus samarensis”): very anterior cervical vertebra (ca. Cv. 3); PIN 3200/472: anterior or middle cervical vertebra lacking most of the neural arch; PIN 3200/212: posterior dorsal vertebra; PIN 2243/167, 2252/384, 386: anterior caudal vertebrae lacking the transverse processes and distal portion of the neural spine.

Emended diagnosis. Small archosauromorph that differs from other diapsids in the following unique combination of features: vertebrae with a deep fossa present laterally to the base of the neural spine; anterior and middle cervical vertebrae with a shelf-like laterally flaring, thick tuberosity projected posteriorly from the base of the diapophysis along the lateral surface of the centrum, and an anterodorsally-to-posteroventrally oriented, thin lamina that delimits the anterolateral border of the fossa placed laterally to the base of the neural spine; and posterior cervical and dorsal vertebrae lacking an anteroventrally-to-posterodorsally oriented bulbous tuberosity placed on the centrodiapophyseal fossa (tuberosity present in Chasmatosuchus magnus).

Figure 11: Chasmatosuchus rossicus.
(A) holotype posterior cervical vertebrae (PIN 2252/381) and (B, C: PIN 3200/217; E, F: PIN 2424/6, holotype of Tsylmosuchus samariensis, mirrored) referred anterior cervical vertebrae; and Chasmatosuchus magnus (D, G) referred anterior cervical vertebra (PIN 3361/13, holotype of “Gamosaurus lozovskii,” mirrored) in left lateral (A, B), ventral (C, F, G), and right lateral (D, E) views. Numbers indicate character-states scored in the data matrix and the arrows indicate anterior direction. Abbreviation: dr, diagonal ridge. Scale bars equal 5 mm.

Remarks. Chasmatosuchus rossicus was named by Huene (1940) based on two articulated posterior cervical vertebrae (PIN 2252/381) (Fig. 11A) and a referred proximal end of a left tibia (PIN 2355/25). In the same contribution, Huene (1940) erected a second species for the genus, “Chasmatosuchus parvus,” based on an isolated probable middle cervical centrum (PIN 2252/382). However, this second species was synonymized with Chasmatosuchus rossicus by Tatarinov (1961) and referred to Microcnemus efremovi by Sennikov (1995b). The referral of the isolated proximal end of tibia to Chasmatosuchus rossicus is problematic because of the absence of overlapping features with the type specimen. As a result, this tibia is not included here within the hypodigm of Chasmatosuchus rossicus. Nevertheless, some cervical, dorsal and caudal vertebrae can be referred to Chasmatosuchus rossicus because of the presence of a unique combination of features not present in other archosauriforms (contra Gower, 1994), including a very deep, anteroposteriorly elongated fossa placed immediately lateral to the base of the neural spine. In addition, the cervical vertebrae of Chasmatosuchus rossicus possess an anterodorsally-to-posteroventrally oriented, thin ridge that delimits the anterolateral border of the fossa placed laterally to the base of the neural spine and extends onto the lateral surface of the base of the prezygapophysis. The presence of this lamina is only shared with “Tsylmosuchus samarensis,” named on the basis of an anterior-middle cervical vertebra (Figs. 11E and 11F) from the same stratigraphic level as Chasmatosuchus rossicus (“Tsylmosuchus samarensis” was considered a nomen dubium by Gower (1994)), and cervical and anterior dorsal proteroschid-like vertebrae collected in the Lower Triassic Panchet Formation of India (e.g., GSI 2111, 2116). However, the anterior and middle cervical vertebrae of Chasmatosuchus rossicus and “Tsylmosuchus samarensis” differ from the Panchet proterosuchid vertebrae in the presence of a shelf-like laterally flaring, thick tuberosity projected posteriorly from the base of the diapophysis along the lateral surface of the centrum, a condition that is only shared with Chasmatosuchus magnus and “Gamosaurus lozovskii” (Figs. 11B11G). Therefore, the unique combination of characters present in Chasmatosuchus rossicus and “Tsylmosuchus samarensis” suggests that these species are synonymous. The presence of the shelf-like tuberosity is also present in the type anterior cervical and single known specimen of the type species of the genus Tsylmosuchus, Tsylmosuchus jakovlevi (PIN 4332/1), and strongly suggests that it is a proterosuchian-grade archosauriform rather than a suchian archosaur, contrasting with its original assignment (Sennikov, 1990). In addition, the third species of the genus, Tsylmosuchus donensis, is distinguished only tentatively from the other species because of their general anatomical similarities (Sennikov, 1990; Gower & Sennikov, 2000) and may also represent a proterosuchian-grade archsauriform. Tsylmosuchus jakovlevi and Tsylmosuchus donensis cannot be clearly distinguished from Chasmatosuchus rossicus and Chasmatosuchus magnus beyond some subtle features and probably are nomina dubia, as was previously proposed by Gower (1994).

Chasmatosuchus magnus Ochev, 1979 (=“Jaikosuchusmagnus (Ochev, 1979), =“Gamosaurus lozovskiiOchev, 1979)

Age. Late Olenekian, late Early Triassic (Ochev, 1979; Gower & Sennikov, 2000).

Locality. Rassypnaya locality, Orenburg region, Russia (Ochev, 1979; Gower & Sennikov, 2000).

Stratigraphic horizon. Upper Yarenskian Gorizont (Ochev, 1979; Gower & Sennikov, 2000).

Holotype. PIN 951/65: anterior cervical vertebra.

Referred material. PIN 3361/13 (holotype of “Gamosaurus lozovskii”): anterior or middle cervical vertebra; PIN 3361/94, 183: two anterior or middle cervical vertebrae, respectively, lacking most of the neural arch; PIN 3361/14: posterior cervical vertebra; PIN 3361/213, 214: anterior dorsal vertebrae lacking most of the neural arch.

Emended diagnosis. Small archosauromorph that differs from other diapsids in the following combination of features: vertebrae with a deep fossa present laterally to the base of the neural spine; anterior and middle cervical vertebrae with a shelf-like laterally flaring, thick tuberosity projected posteriorly from the base of the diapophysis along the lateral surface of the centrum; and posterior cervical and dorsal vertebrae with an anteroventrally-to-posterodorsally oriented bulbous tuberosity placed on the centrodiapophyseal fossa.

Remarks. Two putative proterosuchids have been described from the upper Olenekian Yarenskian Gorizont of Russia: “Gamosaurus lozovskii” and Chasmatosuchus magnus (Ochev, 1979). The holotype of “Gamosaurus lozovskii” is an isolated partial anterior cervical vertebra (PIN 3361/13) (Ochev, 1979) (Figs. 11D and 11G), and Sennikov (1995b) referred to this species a middle (PIN 3361/213) and a posterior (PIN 3361/214) cervical vertebrae. The holotype of Chasmatosuchus magnus is an isolated anterior cervical vertebra (PIN 951/65), and Ochev (1979) referred to this species some vertebrae from the type horizon and the underlying Ustmylian Gorizont, as well as a fibula from the type locality and horizon. Subsequently, Sennikov (1990) erected the new genus “Jaikosuchus” for the species, resulting in the new combination “Jaikosuchusmagnus. He also restricted the referred material of this species to a single neural arch. “Gamosaurus lozovskii” is considered here a subjective junior synonym of Chasmatosuchus (=“Jaikosuchus”) magnus because the anterior cervical vertebrae of the former species are identical in morphology to the holotype of Chasmatosuchus magnus and they share the presence of a strongly developed, shelf-like tuberosity on the lateral surface of the centrum that extends posteriorly from the base of the diapophysis. This feature is not present in other basal archosauromorphs with the exception of Chasmatosuchus rossicus. The distinction between Chasmatosuchus magnus and Chasmatosuchus rossicus is problematic because their type specimens belong to different regions of the cervical series, but at least one feature (i.e., posterior cervical and dorsal vertebrae with an anteroventrally-to-posterodorsally oriented bulbous tuberosity placed on the centrodiapophyseal fossa) present in the lectotype of the latter species and absent in the former species suggests the presence of two different taxa (contra Gower, 1994). As a result, though the distinction between the species is relatively weak, it is followed here and should be tested in the future when further specimens become available. In order to test this hypothesis of synonymy both species (i.e., “Gamosaurus lozovskii” and Chasmatosuchus magnus) were scored as independent terminals in a first phylogenetic analysis and then merged together as a combined Chasmatosuchus magnus in a second phylogenetic analysis (see below).

ChasmatosuchusvjushkoviOchev, 1961

Age. Late Olenekian, late Early Triassic (Ochev, 1961; Gower & Sennikov, 2000).

Stratigraphic horizon. Yarenskian Gorizont, Russia (Ochev, 1961).

Holotype. PIN 2394/4: left premaxilla that lacks most of the prenarial process.

Emended diagnosis. Small archosauromorph that differs from other diapsids in the following unique combination of features: anteroposteriorly narrow base of the prenarial process of the premaxilla; large, subcircular foramina on the anterior surface of the premaxillary body; dorsal flange along the base of the postnarial process of the premaxilla that gradually inceases in height posteriorly; ankylothecodont tooth implantation; more than five tooth positions in the premaxilla; and serrations on both sides of the premaxillary tooth crowns.

Figure 12: “Chasmatosuchus” vjushkovi.
Holotype partial left premaxilla (PIN 2394/4) in (A) lateral and (B) medial views. Numbers indicate character-states scored in the data matrix and the arrows indicate anterior direction. Abbreviations: pap, palatal process; pnp, postnarial process; prp, prenarial process; rap, reabsorption pit. Scale bar equals 5 mm.

Remarks. Ochev (1961) erected the new species “Chasmatosuchusvjushkovi based on an isolated premaxilla (Fig. 12), but this author stated that the assignment of this new species to the genus Chasmatosuchus was very tentative. The overall morphology of the holotype is very similar to that of other archosauriforms with a strongly downturned premaxilla, such as Archosaurus rossicus, Proterosuchus spp., and Sarmatosuchus otschevi (Ezcurra, Butler & Gower, 2013). Indeed, “Chasmatosuchusvjushkovi shares with these species the presence of more than five premaxillary teeth with ankylotheocodont implantation, and a palatal process distinctly divergent from the main axis of the postnarial process, which indicates the presence of a strongly downturned premaxilla (PIN 2394/4). The postnarial process possesses a dorsal flange that increases gradually in height posteriorly, resembling the condition in Archosaurus rossicus (PIN 1100/55), Proterosuchus fergusi (BP/1/3993, RC 846), Proterosuchus goweri (NMQR 880), and “Chasmatosaurusyuani (IVPP V4067, 36315). By contrast, the dorsal flange on the postnarial process of Sarmatosuchus otschevi increases abruptly in height posteriorly at its base and forms a distinct inflexion with the rest of the dorsal margin of the process in lateral view (PIN 2865/68-9). The prenarial process of “Chasmatosuchusvjushkovi possesses an anteroposteriorly narrow base, as occurs in Sarmatosuchus otschevi (PIN 2865/68-9), but contrasting with the deeper base of the process present in Archosaurus rossicus (PIN 1100/55), Proterosuchus fergusi (BP/1/3993, RC 846), Proterosuchus goweri (NMQR 880), and “Chasmatosaurusyuani (IVPP V4067, 36315). Therefore, “Chasmatosuchusotschevi possesses a combination of features absent in other archosauriforms with a downturned premaxilla and seems to be a valid species based on the currently available evidence (contra Gower, 1994).

Proterosuchid from Long Reef

Age. Middle Early Triassic (Kear, 2009).

Locality. Long Reef, noth of Sydney, New South Wales, Australia (Kear, 2009).

Stratigraphic horizon. Bulgo Sandstone, Narrabeen Group, Sydney Basin (Kear, 2009).

Material. SAM P41754: two associated anterior dorsal vertebrae, one of them missing most of the neural arch.

Remarks. Kear (2009) reported the discovery of two associated archosauriform anterior dorsal vertebrae from the Early Triassic Sydney Basin, which represented the first occurrence of a diapsid in this stratigraphic unit. These vertebrae were interpreted as belonging to a proterosuchid because of their anteroposteriorly elongate centra, dorsal neural spines with height greater than length, the possible presence of intercentra, double-headed rib articulations and well-developed distal tables on the neural spines. This specimen was included in the present phylogenetic analysis to test quantitatively its affinities for the first time.

Koilamasuchus gonzalezdiazi Ezcurra, Lecuona & Martinelli, 2010

Age. Ladinian–Carnian, Middle–Late Triassic (Ottone et al., 2014). This age is based on a single radioisotopic date, but correlations based on vertebrate biostratigraphy suggest an Early Triassic age (Bonaparte, 1981; Martinelli, De la Fuente & Abdala, 2009; Ezcurra, Lecuona & Martinelli, 2010).

Locality. Agua de los Burros locality, 35 km south of the city of San Rafael, Mendoza Province, Argentina (Bonaparte, 1981; Ezcurra, Lecuona & Martinelli, 2010).

Stratigraphic horizon. Quebrada de Los Fósiles Formation, Puesto Viejo Group (Bonaparte, 1981; Ezcurra, Lecuona & Martinelli, 2010).

Holotype. MACN-Pv 18119: very well preserved natural external molds of three dorsal vertebrae, at least six osteoderms, a dorsal rib, a probable gastralium, a chevron, a humerus, a probable radius, an ilium, an incomplete ungual phalanx, two metapodial fragments, and some indeterminate bone fragments.

Diagnosis. Koilamasuchus gonzalezdiazi is a small diapsid (total length of ca. 50 cm) distinguished among archosauriforms by the following combination of features (autapomorphy indicated with as asterisk): dorsal vertebral centra with a deep, well-defined, and ovoid lateral fossa; dorsal neural spines moderately tall and sub-triangular in lateral view; dorsal rib with a laterally curved proximal end and a sharp medial inflection below it, deep longitudinal sulcus on the proximal two-thirds of the shaft, and holocephalous; humerus with strongly expanded proximal and distal ends; oblique tuberosity on the shaft of the humerus*; ilium with well-developed preacetabular process; and presence of osteoderms (Ezcurra, Lecuona & Martinelli, 2010: 1436).

Remarks. Bonaparte (1981) reported and briefly described the remains of a proterosuchid from the Early Triassic of western Argentina (but more recently reinterpreted as Middle–Late Triassic in age; Ottone et al., 2014). This specimen was mostly overlooked in the scientific literature until it was redescribed by Ezcurra, Lecuona & Martinelli (2010). These authors found a unique combination of features in MACN-Pv 18119 to support the erection of the new genus and species Koilamasuchus gonzalezdiazi. Ezcurra, Lecuona & Martinelli (2010) included this species in a quantitative phylogenetic analysis and recovered it as more crownward than the putative proterosuchids Proterosuchus spp., Sarmatosuchus otschevi and Fugusuchus hejiapanensis, and as the sister-taxon of erythrosuchids and more crownward archosauriforms.

Kalisuchus rewanensis Thulborn, 1979

Age. Induan, earliest Triassic (Warren & Hutchinson, 1990; Warren, Damiani & Yates, 2006).

Locality. The Crater locality, 11 km south of Rewan, central Queensland, Australia (Thulborn, 1979).

Stratigraphic horizon. Lower beds of the upper part of the Arcadia Formation, Rewan Group (Thulborn, 1979).

Holotype. QM F8998: partial left maxilla.

Emended diagnosis. Medium-sized archosauriform distinguished from other archosauromorphs by the following unique combination of features: absence of antorbital fossa on the ascending and horizontal processes of the maxilla; vertical ascending process of the maxilla with a very slightly concave anterior border of the antorbital fenestra; absence of a maxillo-nasal tuberosity; more than 14 maxillary tooth positions; and teeth with ankylothecodont tooth implantation.

Remarks. Kalisuchus rewanensis was erected by Thulborn (1979) on the basis of an isolated maxilla (QMF 8998) (Figs. 13A, 13C and 13D) and multiple referred cranial and postcranial isolated bones from different localities of the Arcadia Formation. The assignment of the referred specimens to Kalisuchus rewanensis is problematic because of the lack of overlapping features with the holotype. The referred specimens of Kalisuchus rewanensis that were available for study first-hand (most of the bones figured by Thulborn (1979) are not currently housed in the QMF collection and should be considered lost at present, M Ezcurra, pers. obs., 2012) possess a morphology consistent with that of a non-archosaurian archosauriform, but they do not possess a combination of apomorphies congruent with those expected in only one archosauriform subclade. Indeed, the holotype of Kalisuchus rewanensis seems to have an intermediate morphology between that of Proterosuchus spp. and erythrosuchids. As a result, the scorings for Kalisuchus rewanensis were based upon its holotype only, in order to avoid the artefacts that a chimaeric taxon composed of multiple non-closely-related taxa could potentially cause in character optimizations and ultimately in the tree topologies. A first-hand study of the holotype maxilla of Kalisuchus rewanensis (QM F8998) resulted in a substantial reinterpretation of the element and, therefore, it is redescribed as follows.

Figure 13: Kalisuchus rewanensis.
(A, C, D) Holotype partial left maxilla (QM F8998) and close up of an erupting posterior maxillary crown, and (B) formerly referred right pterygoid (QM F9521) in (A) lateral; (C) medial; and (B, D) ventral views. Numbers indicate character-states scored in the data matrix and the arrows indicate anterior direction. Abbreviations: ar, anterior ramus; asp, ascending process; f.ju, facet for articulation with the jugal; hp, horizontal process; lr, lateral ramus; ppr, palatal process; pr, posterior ramus. Scale bars equal 1 cm in (A–D), and 1 mm in the close up.

The holotype of Kalisuchus rewanensis was originally interpreted as a right maxilla by Thulborn (1979: 332, 333), with the presence of an unusual articulation with the premaxilla: “at the front of the maxilla a dorsal groove received the sub-narial ramus of the premaxilla in normal archosaur fashion, but lateral to this there was a more extensive secondary contact missing the posterior half.” However, the holotype is reidentified here as a left maxilla and the unusual secondary contact is reinterpreted as the palatal process (Fig. 13C: ppr), which closely resembles that present in other basal archosauriforms (e.g., Garjainia prima: PIN 951/55). Furthermore, a fragment of tooth bearing bone was located in the collection (collected from the same locality as the holotype but after the publication of Kalisuchus rewanensis; R. Thulborn field note housed with the specimen) that fits perfectly with the cleanly broken margin of the anterior half of the horizontal process. This distal half of the horizontal process preserves interdental plates on the same face of the bone as the shelf-like process, demostrating clearly that the latter structure is on the medial surface and that the element is a left maxilla (contra Thulborn, 1979).

The anterior tip of the maxilla is damaged, but the position of the palatal process indicates that only a very small portion of the anterior process is missing. As a result, the anterior process of the maxilla is proportionally very short in comparison with the length of the horizontal process, resembling the condition in an isolated archosauriform maxilla from the Early Triassic of South Africa (NMQR 3570), Fugusuchus hejiapanensis (Cheng, 1980) and erythrosuchids (e.g., Erythrosuchus africanus: BP/1/5207; Garjainia prima: PIN 2394/5-1). By contrast, the anterior process of the maxilla is proportionally longer in Proterosuchus fergusi (SAM-PK-11208; RC 846), Proterosuchus alexanderi (NMQR 1484), Proterosuchus goweri (NMQR 880), and “Chasmatosaurusyuani (IVPP V4067, 36315). The anterodorsal margin of the anterior process of the maxilla in Kalisuchus rewanensis is broken and, as a result, the shape of the transition between the anterior and ascending processes cannot be determined. The anterior tip of the maxilla possesses a dorsoventrally concave and anteroventrally-to-posterodorsally oriented depression that represents part of the facet for reception of the postnarial process of the premaxilla. The maxilla curves slightly laterally in ventral or dorsal view, but to a lower degree than in Proterosuchus goweri (NMQR 880). The ascending process of the maxilla lacks its anterior margin and distal end. This process is very dorsoventrally tall and vertical, resulting in a broadly, very gently concave anterior border of the antorbital fenestra in lateral view, as occurs in the isolated archosauriform maxilla from South Africa (NMQR 3570), and contrasting with the more concave border present in other basal archosauriforms (e.g., Proterosuchus fergusi: SAM-PK-11208, RC 846; Fugusuchus hejiapanensis: Cheng, 1980; Erythrosuchus africanus: BP/1/5207). There is no antorbital fossa on the preserved portion of the ascending process (i.e., immediately anterior to the antorbital fenestra), neither on the horizontal process, as occurs in Proterosuchus spp. (e.g., Proterosuchus fergusi: SAM-PK-11208, RC 846; “Chasmatosaurusyuani: IVPP V4067, 36315) and Fugusuchus hejiapanensis (Cheng, 1980). The base of the asending process is medially inset with respect to the anterior and horizontal processes and its lateral surface is anteroposteriorly convex, contrasting with the flatter lateral surface of the maxilla of proterosuchids (e.g., Proterosuchus fergusi: SAM-PK-11208, RC 846; “Chasmatosaurusyuani: IVPP V4067, 36315). The ascending process of the maxilla of Kalisuchus rewanensis gradually narrows transversely, becoming laminar towards its distal end. Articular facets for the nasal and lacrimal are not preserved. The ventral border of the antorbital fenestra, on the horizontal process, is concave in lateral view, resembling the condition in other early archosauriforms with the exception of Tasmaniosaurus triassicus (Ezcurra, 2014).

The medial surface of the maxilla is dorsoventrally convex above the alveolar margin at the anterior end and on the base of the horizontal processes. The distal half of the horizontal process is flat. The palatal process is placed immediately above the alveolar margin of the bone and curved ventrally in medial view. As a result, the distal end of the process is distinctly anteroventrally oriented in a stronger degree than in erythrosuchids (e.g., Garjainia prima: PIN 951/55), which may indicate that the premaxilla of Kalisuchus rewanensis was strongly downturned. The dorsal surface of the palatal process possesses a series of longitudinal striations on its most anterior end that merge gradually with the rest of the surface of the bone posteriorly. The medial surface of the ascending process is anteroposteriorly convex immediately anterior to the border of the antorbital fenestra. This convex surface delimits posteriorly an extensive, shallowly concave fossa. A pair of large, medial foramina is placed below the ascending process and level with the mid-height of the horizontal process. The most anterior foramen opens anteroventrally and the most posterior one is more ventrally placed and opens mainly ventrally. The medial surface of the horizontal process possesses a faint facet that becomes dorsoventrally higher anteriorly and probably articulated with the palatine. The dorsal surface of the horizontal process possesses a laminar, laterally placed vertical lamina. This lamina delimits laterally a longitudinal groove on the posterior half of the process, which may have received the anterior process of the jugal. If this was the case, the maxilla and jugal possessed an extensive, diagonal suture, as occurs in Proterosuchus fergusi (SAM-PK-11208).

The alveolar margin of the maxilla is rather damaged and there are 14 preserved alveoli, but the most posterior alveoli are missing. The alveoli are oval in ventral view, with an anteroposterior main axis. Partial teeth are preserved in the fourth, sixth, tenth and twelfth alveoli, but the most complete crown is placed in the fourth tooth socket. The teeth are ankylosed to the bone and the crowns are labiolingually compressed, distally recurved and with distal denticles along most of the margin and mesial denticles restricted to the apical half, resembling the condition in other archosauriforms (Nesbitt, 2011). Interdental plates are preserved on the posterior half of the horizontal process, though they are not well preserved. The interdental plates seem to have been sub-triangular to pentagonal, and their medial surfaces are ornamented with multiple pits.

One of the referred specimens that also deserves comment is the bone interpreted by Thulborn (1979) as a left jugal (QM F9521) (Fig. 13B). Thulborn (1979) thought that this putative jugal possessed a very strange morphology, with a ventrolateral projection below the anterior border of the orbit and a suture with the postorbital inverted from the common diapsid condition (i.e., with the postorbital articulating posteriorly to the jugal). This bone is reinterpreted here as a right pterygoid, with a morphology completely congruent with that present in other archosauriforms, such as Erythrosuchus africanus (NHMUK PV R3592) and Sarmatosuchus otschevi (PIN 2865/68-2). QM F9521 preserves the base of the anterior ramus, most of the posterior ramus and a complete lateral process. The facet interpreted by Thulborn (1979) as the articulation with the postorbital is reinterpreted as the facet to receive the ectopterygoid, whereas the supposed unusual ventrolateral flange is reinterpreted as the projection that partially wraps the distal end of the basipterygoid process of the parabasisphenoid in the basal articulation. The ventral surface of the base of the anterior ramus was originally partially covered with matrix, but after some repreparation of the specimen it was possible to determine the absence of palatal teeth, resembling the condition present in erythrosuchids (Gower, 2003; Ezcurra, Butler & Gower, 2013).

Fugusuchus hejiapaensis Cheng, 1980

Age. Late Olenekian–early Anisian, Early–Middle Triassic (Cheng, 1980).

Locality. Fugu County, Shanxi Province, People’s Republic of China (Cheng, 1980).

Stratigraphic horizon. Heshanggou Formation (Cheng, 1980).

Holotype. GMB V 313: fairly complete skull, an intercentrum, ulna, radius, and partial manus (modified from Parrish, 1992).

Emended diagnosis. Medium-sized archosauriform distinguished from other archosauromorphs by the following unique combination of features: anterior process of the maxilla shorter than the antorbital fenestra; less than 20 tooth positions in the maxilla; absence of maxillo-nasal tuberosity; posterior process of jugal with a semi-circular ventral expansion; squamosal forming a broadly concave posterodorsal corner of the infratemporal fenestra; otoccipial with a deep, teardrop-shaped fossa laterally to the foramen magnum; and sub-horizontal parabasisphenoid in lateral view.

Remarks. Cheng (1980) erected Fugusuchus hejiapaensis and provided a description in Chinese of the specimen. This author assigned Fugusuchus hejiapaensis to the Proterosuchidae, but subsequently Parrish (1992) recovered this species as the most basal member of Erythrosuchidae in a cladistic analysis. Gower & Sennikov (1996) redescribed and figured in detail the braincase of this species and recovered it as the sister-taxon of Proterosuchus spp. based on a phylogenetic analysis restricted to braincase characters. The same result was also recovered by Gower & Sennikov (1997) using characters of the entire skeleton. Ezcurra, Lecuona & Martinelli (2010) found Fugusuchus hejiapaensis in a trichotomy composed of Sarmatosuchus otschevi and other archosauriforms to the exclusion of Proterosuchus spp., thus resulting in a paraphyletic Proterosuchidae. Gower (1994) stated that the premaxilla indentified by Cheng (1980) is poorly preserved, incomplete and even possibly misindentified. In addition, Gower (1994) did not include the putative quadratojugal in his revised reconstruction of the skull of Fugusuchus hejiapaensis. The quadratojugal is reinterpreted here as an ectopterygoid (GMB V 313, unpublished photographs).

Sarmatosuchus otschevi Sennikov, 1994

Age. Anisian, early Middle Triassic (Tverdokhlebov et al., 2003; Lucas, 2010).

Locality. Locality Berdyanka 11, near Mikhailovka village, Berdyanka River basin, Sol-Iletsk district, Orenburg region, southern Cis-Urals, Russia (Gower & Sennikov, 1997).

Stratigraphic horizon. Upper part of the Donguz Gorizont (Gower & Sennikov, 1997).

Holotype. PIN 2865/68: partial skeleton of a single individual, including right premaxilla, right squamosal, incomplete right frontal, incomplete right parietal, right and left quadrates and incomplete jugals, left pterygoid and palatine, braincase without laterosphenoid and cultriform process, right dentary, both probable splenials, right prearticular, isolated teeth, second to eleventh presacral vertebrae, two isolated dorsal centra, one caudal vertebra, ribs, left and right scapulocoracoid, left ulna, and unidentified bone fragments (modified from Gower & Sennikov, 1997).

Diagnosis. Gower & Sennikov (1997: 62) diagnosed Sarmatosuchus otschevi as an archosauriform with estimated total body length of approximately two metres and distinguished from other archosauromorphs by the following unique combination of features: premaxilla downturned; jugal with slender anterior, and broad, semi-elliptical posterior processes; large foramen between quadrate and quadratojugal; teeth present on palatine and palatal ramus of pterygoid, but absent from posteroventral flange of pterygoid; braincase relatively short and high; intercentra present; centra of cervicals as tall as they are long; pectoral ribs three-headed; and scapula and coracoid relatively short and broad. In addition the following autapomorphy distinguishes Sarmatosuchus otschevi from other archosauromorphs: premaxilla with a dorsal flange on the postnarial process that increases abruptly in height posteriorly at its base and forms a distinct inflexion with the rest of the dorsal margin of the process in lateral view.

Remarks. Sennikov (1994) erected Sarmatosuchus otschevi based on a partial skeleton that represents the most complete specimen of a putative proterosuchid from Russia. This species was subsequently described in detail and included for the first time in a quantitative phylogenetic analysis by Gower & Sennikov (1997). These authors recovered Sarmatosuchus otschevi within a monophyletic Proterosuchidae, together with Proterosuchus spp. and Fugusuchus hejiapanensis. More recently, Ezcurra, Lecuona & Martinelli (2010) found Sarmatosuchus otschevi as the sister-taxon of erythrosuchids and more crownward archosauriforms.

Guchengosuchus shiguaiensis Peng, 1991

Age. Late Olenekian–early Anisian, late Early–early Middle Triassic (Peng, 1991; Fröbisch, 2009).

Locality. Gucheng, Fugu County, Shanxi Province, People’s Republic of China (Peng, 1991).

Stratigraphic horizon. Lower Ermaying Formation (Peng, 1991).

Holotype. IVPP V8808: left maxilla, partial skull roof, left pterygoid, partial braincase, posterior portion of the right hemimandible, two anterior–middle cervical vertebrae; one probable anterior dorsal lacking most of the centrum; a fragment of presacral vertebra; four cervical and dorsal ribs; partial right scapula, humerus, ulna, and radius, a metatarsal, and an ungual pahalanx.

Emended diagnosis. Medium-sized archosauriform distinguished from other archosauromorphs by the following unique combination of features (autapomorphies indicated with an asterisk): secondary antorbital fenestra formed by maxilla, nasal and probably premaxilla; maxilla with 14 tooth positions and ankylothecodont tooth implantation; maxilla without maxillo-nasal tuberosity and antorbital fossa; pterygoid without palatal teeth; anterior–middle cervical vertebrae with a strongly transversely convex and rugose distal expansion of the neural spine*; three-headed cervico-dorsal rib; and scapular blade with strongly concave posterior margin.

Remarks. Guchengosuchus shiguaiensis was erected by Peng (1991) based on a partial skeleton. This species has not been frequently mentioned in the scientific literature and has never been included in a quantitative phylogenetic analysis. Unfortunately, several of the bones originally figured and described by Peng (1991) could not be located in the collection of the IVPP and may be lost (scapula and limb bones), and other bones have been damaged (maxilla and pterygoid) since the original description. A detailed redescription of Guchengosuchus shiguaiensis is currently in preparation by the author and colleagues.

Cuyosuchus huenei Reig, 1961

Age. Late Carnian–early Norian, early Late Triassic (Spalletti, Fanning & Rapela, 2008; Ezcurra, Butler & Gower, 2013).

Locality. Cerro Bayo locality, Bajada de la Obligación, southwest of Mendoza city, Las Heras Department, Mendoza Province, Argentina (Rusconi, 1951).

Stratigraphic horizon. Cacheuta Formation, Cuyo Basin (Rusconi, 1951).

Holotype. MCNAM 2669: partial skeleton, including a left jugal, cervical, dorsal, sacral and caudal vertebrae, scapular and pelvic girdle bones and forelimb and hindlimb elements.

Diagnosis. Desojo, Arcucci & Marsicano (2002: 144) rediagnosed Cuyosuchus huenei as an archosauriform distinguished from other archosauromorphs by the following unique combination of features (autapomorphies marked with an asterisk): cervical and first dorsal vertebrae with anterior articular laminae that limit a cavity on each side of the neural arch; first to third caudal vertebrae the tallest of the vertebral column*; sub-rectangular scapular blade, well expanded anteroposteriorly, with the presence of a rounded coracoid; low iliac blade; subcircular, finely pitted, ventral osteoderms lacking articular facets*.

Remarks. Cuyosuchus huenei from the Late Triassic of western Argentina was originally assigned to the temnospondyl Chigutisaurus (Rusconi, 1951), but later reinterpreted as a proterosuchian thecodont and named by Reig (1961). Subsequently, Tatarinov (1961) and Hughes (1963) considered Cuyosuchus huenei an erythrosuchid and a junior synonym of Erythrosuchus africanus. However, Charig & Reig (1970: Fig. 6) interpreted Cuyosuchus huenei as a distinct erythrosuchid and, more recently, Desojo, Arcucci & Marsicano (2002) considered it as an archosauriform closer to crown archosaurs than to erythrosuchids. Thus, Cuyosuchus huenei would be among the youngest known non-archosaurian archosauriforms, but it has not yet been included in a quantitative phylogenetic analysis. A partial left jugal was identified among the indeterminate bones of the holotype during a recent first-hand restudy of the specimen. A detailed redescription of the species is currently in preparation by the author and colleagues.

Garjainia prima Ochev, 1958

Age. Late Olenekian, late Early Triassic (Ochev, 1958; Gower & Sennikov, 2000).

Locality. Kzyl-Sai (=Kzyl-Say) II 2 locality (locality 29 of Tverdokhlebov et al. (2003)), 0.5–1 km west of the village Andreevka, Akbulak district, Orenburg Province, Russia (Ochev, 1958; Gower & Sennikov, 2000).

Stratigraphic horizon. Petropavlovskaya Svita, Yarengian (=Yarenskian) Gorizont (Ochev, 1958; Gower & Sennikov, 2000).

Holotype. PIN 2394/5 (formerly SGU 104/3-43): partial skeleton of a single individual, including an almost complete skull (PIN 2394/5-1–5-7) and lower jaw (PIN 2394/5-8, 5-9), second to fifth cervical vertebrae (PIN 2394/5-10–5-13), two posterior cervical or anterior dorsal vertebrae (PIN 2394/5-16), at least four dorsal vertebrae (PIN 2394/5-14, 5-15, 5-17–5-19), both scapulae and coracoids (PIN 2394/5-32, 5-33), right clavicle (PIN 2394/5-35), interclavicle (PIN 2394/5-34), left fourth metatarsal (PIN 2394/5-36), several presacral ribs (PIN 2394/5-21–5-31), probable gastralia (PIN 2394/5-37), and some indeterminate fragments of bone (PIN 2394/5-37).

Referred material. Multiple specimens housed at the PIN, which previously composed the hypodigm of “Garjainia (=“Vjushkovia”) triplicostata” (Gower & Sennikov, 2000).

Emended diagnosis. Garjainia prima is a medium-sized erythrosuchid distinguished from other archosauromorphs by the following unique combination of character-states (autapomorphies indicated with an asterisk): premaxilla with a longitudinal groove on the lateral surface of the premaxillary body; nasal with an anteroposteriorly long descending process that forms an extensive longitudinal suture with the maxilla*; antorbital fossa absent on the horizontal process of the maxilla; antorbital fenestra trapezoidal and with an anteroventrally-to-posterodorsally orientated main axis*; prefrontal strongly flared laterally in dorsal view*; skull roof with a longitudinal fossa on its dorsal surface that harbours a longitudinal median prominence in its posterior half*; straight suture between postfrontal and postorbital; basioccipital with a median tuberosity on its ventral surface*; trigeminal cranial nerve (CN V) completely enclosed by prootic*; dentary with a posterodorsal process longer than the central posterior process; and interclavicle with a rhomboidal posterior ramus*.

Remarks. Ochev (1958) erected the new erythrosuchid genus and species Garjainia prima based on a fairly complete skull and associated partial postcranium from the late Early Triassic of Russia. This author described the general anatomy of the species in a series of papers (Ochev, 1958; Ochev, 1975; Ochev, 1981), but a detailed, comprehensive description is still missing. Huene (1960) named “Vjushkovia triplicostata”, a second erythrosuchid genus and species from the same gorizont as Garjainia prima. This new species was based on multiple and very well preserved cranial and postcranial specimens (Huene, 1960). Tatarinov (1961) proposed that both Garjainia and “Vjushkovia” were subjective junior synonyms of Erythrosuchus, and this hypothesis was followed by several later authors (e.g., Hughes, 1963; Ewer, 1965; Romer, 1966; Romer, 1972a; Cruickshank, 1972). However, this synonymy was rejected by Young (1964) and Charig & Reig (1970), and more recent authors (e.g., Parrish, 1992; Sennikov, 1995a; Sennikov, 1995b; Gower & Sennikov, 1996; Gower & Sennikov, 1997; Gower & Sennikov, 2000; Desojo, Arcucci & Marsicano, 2002; Ezcurra, Lecuona & Martinelli, 2010; Ezcurra, Butler & Gower, 2013; Ezcurra, 2014; Ezcurra & Butler, 2015a). Gower & Sennikov (2000) concluded that “Vjushkovia” is a subjective junior synonym of Garjainia, in agreement with previous comments by Kalandadze & Sennikov (1985), Ochev & Shishkin (1988), Sennikov (1995a) and Sennikov (1995b), and that “Garjainia triplicostata” is possibly also a subjective junior synonym of Garjainia prima. This taxonomic decision was recently followed by Gower et al. (2014). Indeed,“Garjainia triplicostata” differs from Garjainia prima only in the absence of palatal teeth on the pterygoid and palatine and the presence of completely thecodont tooth implantation. Both characters may be intraspecificlly variable and the hypothesis of synonymy is followed here because of the extremely similar morphology between the two nominal species. For example, the presence or absence of palatal teeth has been found to be intraspecifically variable in several lepidosauromorph species (Mahler & Kearney, 2006). Therefore, the scorings of Garjainia prima were based on the holotype of the species as well as the hypodigm of “Garjainia triplicostata.”

Garjainia madiba Gower et al., 2014

Age. Late Olenekian, late Early Triassic (Hancox, 2000).

Localities. Farm Driefontein 11, approximately 36 km NE of Senekal and 14 km N of Paul Roux, Thabo Mofutsanyane district municipality, Free State, South Africa (type locality); and several localities to the east and northeast of Senekal, in the same stratigraphic horizon as the holotype, Free State, South Africa (Gower et al., 2014).

Stratigraphic horizon. Burgersdorp Formation, Cynognathus AZ Subzone A, Beaufort Group, Karoo Supergroup, Karoo Basin (Gower et al., 2014).

Holotype. BP/1/5760: right postorbital, right postfrontal and partial frontal in articulation; ventral end of left postorbital; left jugal; right paroccipital process with partial supraoccipital and parts of right prootic in articulation; partial rib; at least four unidentified fragments, some of which likely represent partial skull elements.

Paratypes. Approximately 80 specimens from various localities listed by Gower et al. (2014) and housed at the BP and NMQR palaeontological collections.

Referred material. Sixteen specimens from various localities listed by Gower et al. (2014) and housed at the BP palaeontological collection.

Diagnosis. Gower et al. (2014: 6) distinguished Garjainia madiba from its only congener (Garjainia prima) in having the following character-states (autapomorphies marked with an asterisk): large bosses on the lateral surfaces of the jugal and postorbital*; dorsal end of the quadratojugal somewhat thickened; higher tooth counts for the premaxilla (six versus five) and maxilla (likely more than 14 versus 13 or 14); a longer postacetabular process of the dorsal blade of the ilium* (approximately as long as the acetabular portion of the ilium versus clearly shorter than the acetabular portion of the ilium).

Remarks. Hancox et al. (1995) and Hancox (2000) reported the presence of a Garjainia-like erythrosuchid in the upper Olenekian Cynognathus AZ, Subzone A, of South Africa. Gower et al. (2014) formally described these new erythrosuchid specimens and used them as the basis to erect the new species Garjainia madiba. These authors noted multiple similarities with the Russian erythrosuchid Garjainia prima and discussed qualitatively the phylogenetic relationships of the species. This species is included here in a quantitative phylogenetic anlaysis for the first time.

The holotype of Garjainia madiba (BP/1/5760) is based on cranial bones that probably belong to a single individual, and approximately 80 specimens were considered paratypes and 16 referred material (Gower et al., 2014). Most of the paratype and referred specimens of Garjainia madiba do not preserve overlapping features that can be compared with the holotype and, as a result, their assignment should be considered with caution. Nevertheless, all the bones referred to this species possess morphologies consistent with that of an animal very similar to Garjainia prima (Gower et al., 2014). As was the case for Kadimakara australiensis, the assignment of paratype and referred specimens to Garjainia madiba is taken here as a working hypothesis that will be tested in this phylogenetic analysis and by future discoveries of more complete, articulated specimens of the species.

Erythrosuchus africanus Broom, 1905

Age. Early Anisian, early Middle Triassic (Hancox, 2000).

Localities. Oorlogsfontein, Kraai River, a few miles east of Aliwal North, Eastern Cape Province, South Africa (type locality); and multiple localities from the type horizon of the species, South Africa (Broom, 1905; Gower, 2003).

Stratigraphic horizon. Burgersdorp Formation, Cynognathus AZ Subzone B, Beaufort Group, Karoo Supergroup, Karoo Basin (Broom, 1905; Gower, 2003).

Holotype. SAM-PK-905: partial postcranial skeleton.

Referred material. Multiple partial skeletons, cranial and postcranial bones housed in the AMNH, BP, GHG, MNHN, NHMUK PV, NMQR, SAM and UMCZ palaeontological collections. All referred specimens are listed by Gower (2003: Appendix I), and the following specimen is added here: MNHN 1869-12, right humerus.

Emended diagnosis. Erythrosuchus africanus is a large archosauriform distinguished from other archosauromorphs by the following unique combination of character-states: skull without a secondary antorbital fenestra; premaxilla with a peg on the posterior edge of the body; postorbital with incised groove on the posterior process; squamosal with a posterodorsally-to-anteroventrally oriented tuck on the lateral surface of the ventral process; quadratojugal very nearly or completely excluded from the infratemporal fenestra by a squamosal-jugal contact; foramen absent between quadrate and quadratojugal; parietal with posteromedial tubercle on the occipital surface of the posterolateral process; pterygoid without palatal teeth; basioccipital and parabasisphenoid excluded from the floor of the foramen magnum; ventral ramus of the opisthotic recessed within stapedial groove; stapedial groove with small bulge; medial wall of otic capsule not fully ossified; metotic foramen undivided; intercentra in presacral vertebral column; dorsal neural arches pierced by subdivided foramina; three-headed ribs in pectoral region; femur with internal trochanter positioned slightly ventral to the proximal end; astragalus spherical; calcaneum plate-like; fourth distal tarsal with ventral peg; first two distal tarsals and centrale absent; and metatarsal III longer than the others (modified from Gower, 2003: 11, 13).

Remarks. See historical background for the species in Gower (2003: 5, 7).

GHG 7433MI

Age. Late Olenekian–early Anisian, late Early–early Middle Triassic (Hancox, 2000).

Occurrence. Burgersdorp Formation, Cynognathus AZ (indeterminate subzone), Beaufort Group, Karoo Supergroup, Karoo Basin, South Africa. Unfortunately, the exact geographical and stratigraphical occurrence of the specimen is unknown.

Material. GHG 7433MI: fairly complete skeleton, including multiple disarticulated cranial bones and an articulated postcranium missing the distal half of the tail.

Remarks. Gower (2003) tentatively referred GHG 7433MI to Erythrosuchus africanus, but he did not justify this assignment. GHG 7433MI is a small erythrosuchid specimen, in comparison with the largest known specimens of Erythrosuchus africanus, with a total preserved length of around 60 cm and a complete total length estimated at around 1 metre. This specimen is the most complete, articulated erythrosuchid skeleton known so far. The bones of GHG 7433MI, mainly the cranial elements, are still covered with matrix and, as a result, several features cannot be determined or assessed confidently. The right maxilla seems to possess a palatal process placed immediately above the alveolar margin of the bone, resembling the condition of Garjainia prima (PIN 951/55) and Garjainia madiba (BP/1/5525), but contrasting with the more dorsally placed palatal process of Erythrosuchus africanus (BP/1/4680) and Shansisuchus shansisuchus (Young, 1964). However, the anterior end of the right maxilla is partially covered with matrix and this observation should be checked in the future after further preparation. The horizontal process of this maxilla increases abruptly in height towards its posteror end and results in an anteroventrally-to-posterodorsally slanting ventral border of the antorbital fenestra, as occurs in Garjainia prima (PIN 2394/5-1), but contrasting with the more horizontal ventral border of the opening of Erythrosuchus africanus (BP/1/5207). There is a large, subrectangular pineal fossa that extends on the dorsal surface of the frontals and parietals, resembling the condition in Erythrosuchus africanus (BP/1/5207), but contrasting with the oval fossa present in Garjainia prima (PIN 2394/5-1) and Shansisuchus shansisuchus (Young, 1964). Immediately anterior to the pineal fossa, there is a circular tuberosity on the median line of the frontals, which is not present in other archosauriforms of which I am aware. The parietal of GHG 7433MI possesses a transversely narrow supratemporal fossa, as occurs in Garjainia prima (PIN 2394/5-1) and Garjainia madiba (BP/1/5525), but contrasting with Erythrosuchus africanus and Shansisuchus shansisuchus, which lack this fossa (Young, 1964; Gower, 2003).

Based on the few comparisons listed above, it seems that GHG 7433MI belongs to a different taxon than Erythrosuchus africanus, but resembles both species of Garjainia in its morphology. A considerable amount of work is needed on this specimen to determine its taxonomic affinities and may shed light on the general body plan of erythrosuchids.

Shansisuchus shansisuchus Young, 1964

Age. Late Anisian, Middle Triassic (Rubidge, 2005; Ezcurra, Butler & Gower, 2013).

Localities. Hsishihwa 56173, Lotzeyue, Wuhsiang County, Shanxi Province, People’s Republic of China (type locality); several localities from the same horizon as the type locality, Wushiang, Ningwu, Yushe and Jingle counties of Shanxi Province, Xinxiang County of the Henan Province, and Jixian County of Heilongjiang Province, People’s Republic of China (Young, 1964; Wang et al., 2013).

Stratigraphic horizon. Upper member of the Ermaying Formation (Young, 1964; Wang et al., 2013).

Holotype. IVPP V2503: skull roof missing the anterior tip of the rostrum.

Paratypes. IVPP V2501, 2502, 2504–2511, 2512, 2513, 2540, 2593: partial skeletons (Young, 1964; Wang et al., 2013).

Referred material. SXMG V 00002: anterior third of an articulated skeleton, including a skull and a series of 14 vertebrae.

Diagnosis. Wang et al. (2013: 1187) diagnosed Shansisuchus shansisuchus as a large erythrosuchid differing from others in the following combination of character-states: six premaxillary teeth; a large subnarial fenestra anterior to the antorbital fenestra; tongue-in-groove articulations between the postnarial process of the premaxilla and nasal and between the premaxilla and maxilla; ascending process of maxilla tall, narrow, and posterodorsally extended; ventral process of the postorbital with a semi-circular projection into the orbit; broad ventral process of squamosal distally forked; and a large, deeply bow-shaped intercentrum tightly anchoring/capping the sharp ventral edges of two neighboring centra together in cervical and at least first eight dorsal vertebrae.

Remarks. Shansisuchus shansisuchus was named and originally described by Young (1964) based on multiple specimens from the Middle Triassic of China. The original description of the species was complemented by detailed descriptions of its braincase and ankle anatomy (Gower, 1996; Gower & Sennikov, 1996), and, more recently, a well-preserved partial, articulated skeleton was reported by Wang et al. (2013). Shansisuchus shansisuchus was included in several phylogenetic analyses focused on proterosuchian archosauriforms and was recovered in all of them as an erythrosuchid (Parrish, 1992; Gower & Sennikov, 1996; Gower & Sennikov, 1997; Ezcurra, Lecuona & Martinelli, 2010).

Shansisuchus kuyeheensis Cheng, 1980

Age. Late Anisian, Middle Triassic (Rubidge, 2005; Ezcurra, Butler & Gower, 2013).

Locality. Hejiachuan, Shenmu County, Shanxi Province, People’s Republic of China (Cheng, 1980).

Stratigraphic horizon. Upper member of the Ermaying Formation (Cheng, 1980).

Holotype. IGCAGS V 314: partial skeleton, including premaxilla, maxilla, dentary, most of the presacral vertebral series, scapula, coracoid and humerus.

Remarks. This species of Shansisuchus was erected and briefly described by Cheng (1980). Gower (1996) stated that there was no strong evidence to consider this species a valid taxon. Indeed, it was not possible to recognize any unique combination of features based on the description and figures of Cheng (1980) and this species might be a nomen dubium. Unfortunately, the holotype and only known specimen of Shansisuchus kuyeheensis was not studied at first-hand because could not be located in its collection and, as a result, its taxonomic validity will not be assessed here.

Chalishevia cothurnata Ochev, 1980

Age. Ladinian, late Middle Triassic (Shishkin et al., 2000).

Localities. Bukobay VII locality, Sol’-Iletsk distrinct, Orenburg Province, Russia (type and paratype localities); Koltaevo locality, Orenburg Province, Russia (paratype locality) (Ochev, 1980; Gower & Sennikov, 2000).

Stratigraphic horizon. Bukobay Gorizont (Ochev, 1980; Gower & Sennikov, 2000).

Holotype. PIN 4366/1 (wrongly cited as PIN 4356/1 by Gower & Sennikov, 2000): left maxilla and both nasals.

Paratypes. PIN 4366/2: partial right quadrate; PIN 4366/3, 8: teeth; PIN 2867/18: partial right nasal.

Referred material. PIN 2867/7: partial right nasal.

Emended diagnosis. Chalishevia cothurnata is a large erythrosuchid that differs from other archosauromorphs in the following combination of features (autapomorphy indicated with an asterisk): accessory antorbital fenestra and fossa*; maxillo-nasal tuberosity; and maxilla with an edentulous anterior tip, mainly vertical ascending process, and oblique, anteroventrally-to-posterodorsally oriented ventral border of the antorbital fossa on the horizontal process*.

Remarks. See comments in Gower & Sennikov (2000: 149).

Youngosuchus sinensis (Young, 1973b)

Age. Anisian–Ladinian, Middle Triassic (Lucas, 2010).

Occurrence. Kelamayi Formation, Xinjiang Autonomous Region, People’s Republic of China (Young, 1973b).

Holotype. IVPP V3239: complete skull and lower jaw, cervical vertebrae, and partial pectoral girdle and forelimbs.

Emended diagnosis. Youngosuchus sinensis is a medium-sized archosauriform that differs from other archosauromorphs in the following combination of features (autapomorphy indicated with an asterisk): skull without secondary antorbital fenestra and maxillo-nasal tuberosity; premaxilla with four tooth positions; maxilla contributes to the border of the external naris; horizontal process of the maxilla with a straight ventral border of the antorbital fenestra; maxilla with an antorbital fossa on the ascending and horizontal processes, but interrupted on the anterior border of the antorbital fenestra; nasal with a dorsally elevated anterior end above the skull roof, giving the skull a “Roman nose” appearance; lateral surface of the jugal with a plate-like prominence, separated anteroventrally from the rest of the bone by a distinct shelf and placed immediately below the ascending process*; neural spines of the cervical vertebrae without spine table; three-headed cervico-dorsal ribs; scapula with a prominent tuber on the posterior edge, just dorsal to the glenoid fossa; and coracoid with a rather well-developed and laterally expanded posterior process.

Remarks. Young (1973b) described a partial skeleton of a putative erythrosuchid from the Middle Triassic of China and used it as the basis for the new species “Vjushkoviasinensis. Subsequently, Kalandadze & Sennikov (1985) reinterpreted this species as a rauisuchid archosaur and transferred it to the new genus Youngosuchus. Nevertheless, Parrish (1992) agreed with the original phylogenetic conclusion of Young (1973b) and returned to the generic assignment of “Vjushkoviasinensis. Indeed, Parrish (1992) found “Vjushkovia triplicostata” and “Vjushkoviasinensis as more closely related to each other than to other erythrosuchids, and Garjainia prima as the most basal erythrosuchid. Gower & Sennikov (2000) concluded that there is no sound morphological basis for a generic distinction between Garjainia and “Vjushkovia”, and that Garjainia prima and “Vjushkovia triplicostata” probably represent a single species. Therefore, these conclusions clearly contradicted the quantitative results recovered by Parrish (1992). After a first-hand study of all of these specimens, the interpretations of Gower & Sennikov (2000) are followed here, and “Vjushkovia” is considered a junior synonym of Garjainia. As a result, the taxonomic assignment of IVPP V3239 as Youngosuchus sinensis is used here.

Dongusia colorataHuene, 1940nomen dubium

Age. Anisian, early Middle Triassic (Tverdokhlebov et al., 2003; Lucas, 2010).

Locality. Donguz I locality, Sol’-Iletsk district, Orenburg Province, Russia (Huene, 1940; Gower & Sennikov, 2000).

Stratigraphic horizon. Donguz Gorizont (Huene, 1940; Gower & Sennikov, 2000).

Holotype. PIN 268/2: dorsal vertebra lacking most of the neural spine.

Remarks. Huene (1940) erected “Dongusia colorata” and interpreted it as a proterosuchid. Tatarinov (1961) considered that this species was an erythrosuchid and even cogeneric with Erythrosuchus. Subsequent authors have regarded “Dongusia” and “Dongusia colorata” as nomina dubia (Young, 1964; Charig & Reig, 1970; Charig & Sues, 1976; Ezcurra, Butler & Gower, 2013) and some of them proposed that PIN 268/2 belongs to a rauisuchid archosaur (Charig & Reig, 1970; Sennikov in Gower & Sennikov, 2000). It is agreed here that this genus and species are nomina dubia, but the taxon was included in the taxonomic sample of the present analysis in order to test the original proposed proterosuchian affinities of the type specimen.

Uralosaurus magnus (Ochev, 1980)

Age. Anisian, early Middle Triassic (Tverdokhlebov et al., 2003; Lucas, 2010).

Locality. Karagachka locality, Sol’-Iletsk district, Orenburg Province, Russia (Ochev, 1980; Gower & Sennikov, 2000).

Stratigraphic horizon. Donguz Gorizont (Ochev, 1980; Gower & Sennikov, 2000).

Holotype. PIN 2973/70: left pterygoid.

Paratypes. PIN 2973/71: right dentary; PIN 2973/72–79: seven teeth.

Emended diagnosis. Uralosaurus magnus is a large archosauriform that can tentatively be distinguished from other archosauromorphs by the following combination of features (autapomorphy indicated with an asterisk): dentary strongly dorsally curved, with eight tooth positions; a pair of blind and relatively shallow fossae placed immediately posterior to the most posterior tooth socket*; and thecodont tooth implantation.

Remarks. Ochev (1980) erected the new species Erythrosuchus magnus from the Anisian of Russia based on a left pterygoid (PIN 2973/70). Ochev (1980) also referred to this species a right dentary (PIN 2973/71) and some isolated teeth from the type locality (PIN 2973/72–79), and tentatively referred some presacral vertebrae from other localities (Ochev, 1980; Gower & Sennikov, 2000). Subsequently, Sennikov (1995b) erected the new genus Uralosaurus and assigned Erythrosuchus magnus to it, resulting in the new combination Uralosaurus magnus. Sennikov (1995b) also referred to Uralosaurus magnus some cranial remains and caudal vertebrae from different localities to that of the holotype. All these elements possess an erythrosuchid-like morphology (Gower & Sennikov, 2000), but there are other species in the same stratigraphic horizon that may possess a similar morphology (e.g., Dongusuchus efremovi). Therefore, only the pterygoid, dentary, and teeth from the same locality are considered here the hypodigm of Uralosaurus magnus. This hypothesis will be tested in the phylogenetic analysis and by subsequent discoveries of associated bones of Uralosaurus magnus from the Donguz Gorizont. The overall morphology of the bones and teeth of Uralosaurus magnus (PIN 2973/70–79) is very similar to that of other erythrosuchids (e.g., Erythrosuchus africanus) and it is difficult to find characters that may support the recognition of Uralosaurus magnus as a distinct taxon. There is a pair of blind and relatively shallow fossae placed immediately posterior to the final tooth socket along the alveolar margin of the referred dentary of Uralosaurus magnus (PIN 2973/71). These fossae are too shallow to have housed teeth and are not present in any other archosauriform of which I am aware. This condition may be related with the lower tooth count (eight alveoli) of PIN 2973/71 in comparison to the dentaries of other erythrosuchids (14–16 tooth positions in Shansisuchus shansisuchus: Young, 1964; 13–14 in Garjainia prima: PIN 2394/5-8, 5-9, 951/30; 14 in Garjainia madiba: NMQR 3051; ≥12 in Erythrosuchus africanus: BP/1/3893). It is not possible to determine here if these fossae are pathological (e.g., as a result of alveolar remodeling), but, together with the very low tooth count, they may support the distinction of Uralosaurus magnus from other erythrosuchid species.

The holotype of Uralosaurus magnus and the entire hypodigm were scored as different terminals in two alternative phylogenetic analyses because of the ambiguous referral of the right dentary and teeth due to the lack of comparable homologous characters with the holotype.

Vancleavea campi Long & Murry, 1995

Age. ?Carnian–Rhaetian, Late Triassic (Hunt, Lucas & Spielmann, 2005; Nesbitt, 2011; Ramezani, Fastovsky & Bowring, 2014).

Localities. PFV 124, Petrified Forest National Park, Apache County, Arizona, USA (type locality). Several other localities in Arizona and Utah and New Mexico and Texas (Long & Murry, 1995; Hunt et al., 2002; Parker & Barton, 2008; Nesbitt et al., 2009; Nesbitt, 2011).

Stratigraphic horizons. Blue Mesa, Mesa Redondo, Monitor Butte, Sonsela, Petrified Forest, Owl Rock and “Siltstone” members of the Chinle, Bull Canyon, Redonda and Tecovas formations (Long & Murry, 1995; Hunt et al., 2002; Parker & Barton, 2008; Nesbitt et al., 2009; Nesbitt, 2011).

Holotype. PEFO 2427: incomplete postcranial skeleton.

Referred material. GR 138: complete skeleton; GR 139: partial disarticulated skeleton; and more fragmentary specimens housed at the PEFO, MNA, UCMP and UMMP palaeontological collections (Long & Murry, 1995; Hunt et al., 2002; Hunt, Lucas & Spielmann, 2005; Parker & Barton, 2008; Nesbitt et al., 2009).

Diagnosis. Nesbitt et al. (2009: 816) dignosed Vancleavea campi on the basis of the following combination of autapomorphies: absence of supratemporal and antorbital fenestrae; large caniniform, and recurved and serrated teeth in each tooth-bearing bone; well-defined depression on the lateral surface of the dentary for the maxillary caniniform tooth; neomorph bone separating the nasals; absence of a lacrimal; ilium lacking an anterior process and bearing a highly reduced posterior process; exoccipitals do not participate in the formation of the occipital condyle; dorsal centra with two paramedian ventral keels and neural spines with dorsal notches at the anterior and posterior ends; five unique osteoderm morphologies, namely teardrop-shaped ventral cervical region osteoderms, diamond-shaped osteoderms with midline keels on the ventral portion of the body, diamond-shaped osteoderms with a pointed anterior process on the lateral sides of the dorsal and caudal regions of the body, thin, mediolaterally compressed appendicular osteoderms, and large, vertically projecting, laterally compressed osteoderms dorsal to the neural spines of the caudal vertebrae.

Remarks. See comments in Nesbitt (2011: 17).

Asperoris mnyama Nesbitt, Butler & Gower, 2013

Age. Late Anisian, early Middle Triassic (Nesbitt et al., 2010).

Locality. U9/1 locality, drainage of the Hita River between the Njalila and Hiasi rivers (exact locality unknown), Songea district, southwestern Tanzania (Nesbitt, Butler & Gower, 2013).

Stratigraphic horizon. Lifua Member, Manda beds, Ruhuhu Basin (Nesbitt, Butler & Gower, 2013).

Holotype. NHMUK PV R36615: well-preserved incomplete skull including much of the right maxilla, nearly complete right premaxilla, much of the right nasal, ventral process of the postorbital, right prefrontal, right frontal, right parietal, much of right postfrontal, and other unidentified skull fragments (Nesbitt, Butler & Gower, 2013).

Diagnosis. Asperoris mnyama has the following unique combination of cranial character-states (autapomorphy indicated with an asterisk): highly sculptured cranial elements including the premaxilla, maxilla, nasal, prefrontal, frontal, postfrontal, and parietal, and highly sculptured, dorsoventrally deep orbital margin of the frontal*; posterodorsal process of the premaxilla fits into a distinct slot into the ventral process of the nasal; robust anteromedially directed palatal process of the maxilla; thecodont dentition; absence of an antorbital fossa on the maxilla anterior and ventral to the antorbital fenestra; dorsoventrally shallow antorbital fenestra; dorsoventrally thick skull roof; absence of a parietal foramen or fossa; and possible presence of a postparietal element (Nesbitt, Butler & Gower, 2013).

Remarks. Asperoris mnyama was recently named and described by Nesbitt, Butler & Gower (2013). These authors found this species as an archosauriform more crownward than Proterosuchus fergusi, but more basal than Euparkeria capensis, phytosaurus and archosaurs.

Euparkeria capensis Broom, 1913

Age. Early Anisian, early Middle Triassic (Rubidge, 2005).

Locality. Site along a road between Aliwal North and Lady Grey (exact location of the site unknown), Eastern Cape Province, South Africa (Dilkes, 1998).

Stratigraphic horizon. Burgersdorp Formation, Cynognathus AZ subzone B, Tarkastad Subgroup, Beaufort Group, Karoo Supergroup, Karoo Basin (Dilkes, 1998).

Holotype. SAM-PK-5867: partial skeleton including a nicely preserved skull and lower jaw.

Referred material. At least 11 individuals housed in the AMNH, GPIT, SAM-PK and UMZC collections (Sookias & Butler, 2013; see Ewer, 1965).

Diagnosis. No formal diagnoses of the genus Euparkeria and the species Euparkeria capensis have ever been provided (Sookias & Butler, 2013), but a detailed revision of the species is currently in preparation and will provide a diagnosis (R Sookias & R Butler, pers. comm., 2015).

Remarks. See comments in Nesbitt et al. (2009: 851).

Dorosuchus neoetus Sennikov, 1989a

Age. Anisian, early Middle Triassic (Tverdokhlebov et al., 2003; Lucas, 2010).

Localities. Berdyanka I (type and paratype locality) and Donguz I (PIN 952/200 locality) localities, Sol’Iletsk district, Orenburg Province, Russia (Sennikov, 1989a; Sennikov, 1989b).

Stratigraphic horizon. Donguz Gorizont (Sennikov, 1989a; Sennikov, 1989b).

Holotype. PIN 1579/61: mostly complete right ilium, complete right femur and complete right tibia, pertaining to a single individual and found in articulation. PIN 1579/67: a fragment of bone identified previously as the distal tip of an ischium (Sennikov, 1989a; Sennikov, 1989b) was reidentified by Sookias et al. (2014a) as the distal part of the postacetabular process of the right ilium of PIN 1579/61 and thus is also considered part of the holotype.

Paratypes. PIN 1579/62: mostly complete braincase; PIN 1579/63: single sacral vertebra lacking the neural spine, in articulation with partial sacral ribs; PIN 1579/64: two articulated proximal caudal vertebrae; PIN 1579/65: single, smaller, caudal vertebral centrum; PIN 1579/66: slightly damaged left and right ilia (smaller than the holotype); PIN 1579/68: single phalanx; PIN 952/200: partial left ilium of a similar size to those of PIN 1579/66 (Sennikov, 1989a; Sennikov, 1989b; Sookias et al., 2014a).

Diagnosis. Sookias et al. (2014a: 5, 6) diagnosed Dorosuchus neoetus as a relatively small (maximum known femur length 98.3 mm) non-crown archosauriform distinguishable on the basis of the following autapomorphies: preacetabular process of the ilium relatively short in comparison with length of pubic peduncle and distally rounded in lateral view; proximal end of tibia 33% wider dorsoventrally than distal end and approximately 70% wider than midshaft, with very little expansion of proximal end ventral to shaft (ratio of dorsal expansion of proximal end to ventral expansion: 0.22), such that dorsal margin of shaft is straight to convex and ventral margin concave in lateral view; proximal projection present proximal to dorsal margin of lateral condyle of tibia in medial view; and outline of distal end of the tibia in distal view rounded, but dorsally tapered. In addition, Sookias et al. (2014a: 6) stated that the holotype (PIN 1579/61) can be also diagnosed on the basis of the following unique combination of characters: preacetabular process of ilium short and rounded distally in lateral view; pronounced supraacetabular crest on ilium; pronounced striations on iliac blade; gently sigmoid femur; and clearly developed attachment ridge for M. caudifemoralis longus (=fourth trochanter) on femur. The paratype braincase (PIN 1579/62) is diagnosable based on the following unique combination of characters: subvertically orientated parabasisphenoid; low ridge on anterior inferior process of prootic below foramen for trigeminal nerve; and ventral ramus of opisthotic only weakly expanded laterally.

Remarks. The hypodigm of Dorosuchus neoetus is composed of the holotype right ilium, femur, and tibia (PIN 1579/61, 67), which were found in articulation and thus represent a single individual, and several paratypes (PIN 1579/62–66, 68) that were collected from the same block as the holotype (Sennikov, 1989a; Sennikov, 1989b; Sookias et al., 2014a). In addition, an isolated partial left ilium (PIN 952/200) is also considered part of the paratype because is very similar in morphology to that of PIN 1579/66 (Sookias et al., 2014a). Sookias et al. (2014a) tentatively accepted the referral of a partial left pterygoid (PIN 1579/69) and a hemimandible (PIN 1579/70) to Dorosuchus neoetus by Sennikov (1995b) and Sennikov (2008), but they tested the effect that the inclusion of these two specimens may have on the phylogenetic relationships of the animal by conducting six alternative phylogenetic analyses. These two referred specimens were found in a different block from that of the type series (Sookias et al., 2014a) and the presence of other basal archosauriforms that could possess a morphologically similar pterygoid and hemimandible in the same horizon as Dorosuchus neoetus (i.e., Dongusuchus efremovi, “Dongusia colorata”) means that this referral should be treated with caution. As a result, I decided here not to include the referred specimens of Dorosuchus neoetus when scorings this taxon; instead, Dorosuchus neoetus is scored based on the type series only.

Sennikov (1989a) referred Dorosuchus neoetus to Euparkeriidae based on its general similar morphology to Euparkeria capensis. Gower & Sennikov (2000) raised doubts about the assignment of Dorosuchus neoetus to Euparkeriidae and Sookias & Butler (2013) listed this species as a possible euparkeriid. Sookias et al. (2014a) redescribed in detail the hypodigm of Dorosuchus neoetus and included this species in a quantitative phylogenetic analysis for the first time. These authors found Dorosuchus neoetus as the sister-taxon of Phytosauria + Archosauria, immediately crownwards of Euparkeria capensis.

Yarasuchus deccanensis Sen, 2005

Age. Anisian, early Middle Triassic (Lucas, 2010).

Locality. Bhimaram village, Pranhita-Godavari Valley, Adilabad district, Andhra Pradesh, India (Sen, 2005).

Stratigraphic horizon. Yerrapalli Formation (Sen, 2005).

Holotype. ISI R 334/9–14: cervical vertebrae; ISI R334/36: first sacral; ISI R 334/37: second sacral; ISI R 334/56: right ilium; ISI R 334/63: left pubis.

Referred material. Multiple specimens collected from the same locality, listed by Sen (2005: 185, 186), and housed in the ISI palaeontological collection.

Diagnosis. Sen (2005: 185) diagnosed Yarasuchus deccanensis as a small (total length approximately 2 meters), long-necked, gracile animal, with a small skull relative to presacral length; elongated cervical vertebrae, cervical neural spine with coarsely crenulated dorsal margin; neural spines high throughout the vertebral column; pectoral girdle delicately built with small coracoid and scapula constricted near the glenoid; and osteoderms coarsely sculptured.

Remarks. Yarasuchus deccanensis was erected by Sen (2005) and assigned to the rauisuchian family Prestosuchidae. Brusatte et al. (2010) included this species for the first time in a phylogenetic analysis and recovered it as the most basal member of Poposauroidea. More recently, the hypodigm of this species was suggested to be a chimera composed of rauisuchian archosaur and prolacertiform bones (Desojo in Lautenschlager & Desojo, 2011; Nesbitt et al., 2013). After a first-hand study of the entire hypodigm of Yarasuchus deccanensis, it was not possible to recognize archosaur or putative prolacertiform apomorphies in the preserved bones (with the exception of the highly homoplastic elongated cervical vertebrae). For example, the maxilla possesses a thecodont tooth implantation and the border of the antorbital fenestra on the horizontal process lacks an antorbital fossa (ISI R334/2), and the femur possesses a fourth trochanter but lacks a posteromedial tuberosity on the proximal end (ISI R334/67), contrasting with the conditions in prolacertiforms (e.g., Protorosaurus speneri, tanystropheids, Prolacerta broomi) and suchian archosaurs (e.g., Arizonasaurus babbitti, Prestosuchus chiniquensis). The cervical vertebrae of Yarasuchus deccanensis are clearly distinct from those of Pamelaria dolichotrachela, as originally recognized by Sen (2005), differing from this allokotosaurian in the presence of a median ventral keel on the centrum, epipophysis on the postzygapophysis, and considerably taller neural spines with an anterior overhang and a rugose distal transverse thickening of the distal end. Therefore, the hypodigm of Yarasuchus deccanensis is not composed of bones that belong to prolacertiforms, rauisuchians or a combination of both, but the anatomy of the species is congruent with that expected for a non-archosaurian archosauriform. As a result, the original hypodigm of the species is retained here and scored as a single terminal.

Dongusuchus efremovi Sennikov, 1988b

Age. Anisian, early Middle Triassic (Tverdokhlebov et al., 2003; Lucas, 2010).

Locality. Donguz I site, about 1 km NW of Perovka village, along the right bank of the Donguz River (within the drainage basin of the Ural River), Sol’-Iletsk district, Orenburg Province, Russia (Sennikov, 1988b; Niedźwiedzki, Sennikov & Brusatte, 2014).

Stratigraphic horizon. Donguz Gorizont (Sennikov, 1988b; Niedźwiedzki, Sennikov & Brusatte, 2014).

Holotype. PIN 952/15-1: left femur.

Referred material. PIN 952/15-2–15-5: four femora.

Diagnosis. Niedźwiedzki, Sennikov & Brusatte (2014: 9) diagnosed Dongusuchus efremovi as a non-archosaurian archosauriform with the following autapomorphies: remarkably gracile femur with a ratio of proximodistal length to minimum midshaft diameter in posteromedial or anterolateral view of >13.0; very deep and curved groove on the proximal surface of the femoral head; and a low, nearly flat and medially displaced posteromedial tuber on the proximal portion of the femur in proximal view, devoid of anteromedial tuber.

This combination of apomorphies is also present in the femora of the hypodigm of Yarasuchus deccanensis and it is not possible to distinguish the two species from each other. Nevertheless, the equivocally referred specimens of Dongusuchus efremovi (sensu Niedźwiedzki, Sennikov & Brusatte, 2014) differ from the same elements in Yarasuchus deccanensis. As a result, Dongusuchus efremovi may potentially be a senior synonym of Yarasuchus deccanensis, but the taxonomic affinities of the equivocally referred specimens of the former species should be resolved in order to shed light on the taxonomy of both taxa.

Remarks. Sennikov (1988b) erected the new genus and species Dongusuchus efremovi based on an isolated complete left femur (PIN 952/15-1). Several additional postcranial bones have been subsequently referred to this species (Sennikov, 1988a; Sennikov, 1988b; Sennikov, 1990; Sennikov, 1995b). Recently, Niedźwiedzki, Sennikov & Brusatte (2014) considered only four femora demonstrably referred specimens (PIN 952/15-2–5), and the other previously referred specimens that cannot be compared directly with the holotype because they lack overlapping features were considered equivocally referred specimens. Niedźwiedzki, Sennikov & Brusatte (2014) conducted alternative phylogenetic analyses testing the effect that the inclusion of the equivocally referred specimens has on the phylogenetic position of the species. The results of these analyses showed that these equivocally referred specimens do not affect the position of Dongusuchus efremovi (Niedźwiedzki, Sennikov & Brusatte, 2014). In the present phylogenetic analysis the scorings for this species were based only upon the holotype and demonstrably referred specimens. As for Dorosuchus neoetus, the presence of other basal archosauriforms in the same horizon as Dongusuchus efremovi (e.g., Dorosuchus neoetus, “Dongusia colorata”) means that caution is required in the referral of bones that do not overlap in morphology with the holotype (e.g., cervical vertebrae, forelimb elements).

Proterochampsa barrionuevoi Reig, 1959

Age. Late Carnian–earliest Norian, early Late Triassic (Rogers et al., 1993; Furin et al., 2006; Martínez et al., 2011).

Localities. Several localities of the Hoyada de Ischigualasto, Ischigualasto Provincial Park, San Juan Province, Argentina (Reig, 1959; Sill, 1967; Martínez et al., 2012).

Stratigraphic horizon. Upper La Peña, Cancha de Bochas and lower Valle de la Luna members of the Ischigualasto Formation, Ischigualasto-Villa Unión Basin (Martínez et al., 2012).

Holotype. PVL 2063: skull with lower jaw and five presacral vertebrae. Dilkes & Arcucci (2012) reported that the vertebrae cannot currently be located.

Referred material. MACN-Pv 18165: partial skull with one hemimandible; MCZ 3408: complete skull with lower jaw and 13 articulated presacral vertebrae and ribs; PVL 2057: partial skull with lower jaw; PVL 2058: skull with lower jaw; PVL 2061: partial skull lacking snout, palate, braincase and lower jaw; PVL 3434: skull lacking premaxillae, most of the temporal region, braincase, and lower jaw; PVSJ 77: complete skull with one articulated and one separate hemimandible.

Diagnosis. Trotteyn, Arcucci & Raugust (2013: 62, 63) diagnosed Proterochampsa barrionuevoi by the following autapomorphies: dermal sculpture consisting of highly nodular protuberances and prominent ridges with smaller periodic nodular growths along their length; antorbital fossa restricted to elongate depression on the maxilla at anterior end of the antorbital fenestra; lateral expansion of premaxillae anterior to contact between premaxilla and maxillae along ventral margin of skull; no fossa along postorbital, squamosal and parietal borders of supratemporal fenestra; large anteriorly curved spine on quadratojugal; exclusion of jugal from suborbital fenestra by contact of maxilla and ectopterygoid; basal tubera of parabasisphenoid faces ventrally rather tan ventrolaterally and projects laterally beyond the basipterygoid process; and a ventrally projecting lamina on the angular. Proterochampsa barrionuevoi is also characterized by the absence of a retroarticular process, occipital wing of the parietal diverges from the midline axis of the skull at an angle of approximately 60°, and dorsoventrally flattened skull with antorbital fenestrae, orbits and supratemporal fenestrae dorsal in orientation, in addition to the dorsal position of the external nares.

Remarks. Proterochampsa barrionuevoi is one of the best-known non-archosaurian archosauriforms (Sill, 1967; Trotteyn, 2011a; Dilkes & Arcucci, 2012), but it was included in quatitative phylogenetic analyses as an independent terminal (and not part of a suprageneric Proterochampsidae) only recently (Dilkes & Arcucci, 2012; Trotteyn & Ezcurra, 2014; Ezcurra, Desojo & Rauhut, 2015). Proterochampsa barrionuevoi has been recovered as the most basal member of the South American proterochampsid radiation and, as a result, it is a key taxon to optimize the ancestral character-states of the group.

Proterochampsa nodosa Barberena, 1982

Age. Late Carnian–earliest Norian, early Late Triassic (Rogers et al., 1993; Langer, 2005; Furin et al., 2006; Martínez et al., 2011).

Locality. Sesmaria do Pinhal, Rio Grande do Sul State, Brazil (Barberena, 1982; Langer et al., 2007).

Stratigraphic horizon. Santa Maria Sequence 2, Hyperodapedon AZ, Rosário do Sul Group, Paraná Basin (Barberena, 1982; Langer et al., 2007).

Holotype. MCP 1694 PV: partial skull and lower jaw.

Emended diagnosis. Trotteyn, Arcucci & Raugust (2013: 66) diagnosed Proterochampsa nodosa as a proterochampsian with a skull that is proportionally similar to the skull of Proterochampsa barrionuevoi; occipital region proportionally higher than in Proterochampsa barrionuevoi; quadrate forms an angle of 90°with the squamosal; ornamented skull with fewer nodules than in Proterochampsa barrionuevoi; elongated nares; and frontal more elongated and whose anterior half is flatter than in Proterochampsa barrionuevoi.

Remarks. This species is known from a rather complete skull that it is very similar to its Argentinean congeneric species Proterochampsa barrionuevoi (Barberena, 1982). Proterochampsa nodosa has been included only recently in a quantitative phylogenetic analysis and its result bolstered the monophyly of Proterochampsa (Ezcurra, Desojo & Rauhut, 2015).

Tropidosuchus romeri Arcucci, 1990

Age. Early Carnian, early Late Triassic (Marsicano et al., 2015).

Locality. Los Chañares type locality, near the mouth of Chañares River, Talampaya National Park, La Rioja Province, Argentina.

Stratigraphic horizon. Lower member of the Chañares Formation (sensu Fiorelli et al., 2013), Ischigualasto-Villa Unión Basin.

Holotype. PVL 4601: articulated skeleton lacking the manus.

Referred material. MCZ 9482: partial skeleton associated with a specimen of Gracilisuchus stipanicicorum; PULR unnumbered: partial postcranium associated with the holotypes of “Lagosuchus talampayensis” (PULR 09) and Gracilisuchus stipanicicorum (PULR 08); PVL 4602: anterior portion of the skull, lower jaw, articulated presacral column, partial pelvic girdle, and both femora, tibiae, and fibulae; PVL 4603: skull and lower jaw with presacral column, partial pelvic girdle, seven articulated caudal vertebrae; and several disarticulated osteoderms; PVL 4604: fairly complete skeleton; PVL 4605: skull and lower jaw with articulated presacral vertebral column, seven proximal caudal vertebrae, seven distal caudal vertebrae, articulated left scapula, coracoid, and humerus, pelvic girdle, both femora, tibiae, and fibulae, articulated left distal tarsals and pes; PVL 4606: skull and lower jaw, articulated presacral vertebral series, sacrum and pelvic girdle, left femur, tibia, fibula, tarsus, and pes; and PVL 4624: left femur, tibia and fibula, and one metatarsal (modified from Trotteyn, Arcucci & Raugust, 2013).

Diagnosis. Trotteyn, Arcucci & Raugust (2013: 78, 79) diagnosed Tropidosuchus romeri as an archosauriform with triangular skull in dorsal view; proportionally large orbits; curved premaxilla at the distal tip; nearly vertical quadrate; occipital crest well developed; ornamentation of the skull in longitudinal crests with different disposition; pterygoid with posterior edges of the wings straight and thickened; internal edge of pterygoid with denticles in alveoli, forming a ‘V’-shaped structure opened posteriorly; vertebral cervico-dorsal zonation more marked; shoulder girdle with rod-like clavicle and interclavicle; ulna without olecranon; femur as long as the tibia; tibia with distal articulation not transverse or longitudinal; and large osteoderms, in one row and one per vertebra, with a well-developed dorsal laminar crest extended axially.

Remarks. See comments in Nesbitt et al. (2009).

Cerritosaurus binsfeldi Price, 1946

Age. Late Carnian–earliest Norian, early Late Triassic (Rogers et al., 1993; Langer, 2005; Furin et al., 2006; Martínez et al., 2011).

Locality. Sanga do Mato, Rio Grande do Sul State, Brazil (Price, 1946; Langer et al., 2007).

Stratigraphic horizon. Santa Maria Sequence 2, Hyperodapedon AZ, Rosário do Sul Group, Paraná Basin (Price, 1946; Langer et al., 2007).

Holotype. CA s/n: complete skull and lower jaw articulated with the first 15 presacral vertebrae, ribs, and osteoderms, and a humerus.

Diagnosis. Trotteyn, Arcucci & Raugust (2013: 68) diagnosed Cerritosaurus binsfeldi as a proterochampsian with a dorsoventrally compressed and ornamented skull roof; ornamentation of the skull roof is more visible in the posterior region of the nasal to the parietal; supratemporal fenestra small and similar in length to the antorbital fenestra; external naris small and oval, surrounded by slit-like depressions on the premaxilla and nasal; and oval osteoderms located on the neural spines, forming one longitudinal row.

Remarks. The holotype and single known specimen of Cerritosaurus binsfeldi is preserved in a concretionary matrix and some bones are strongly taphonomically altered, limiting available information on the palate, braincase, and postcranium. This species was included for the first time in a quantitative phylogenetic analysis by Dilkes & Arcucci (2012) and recovered as the sister-taxon of the early Late Triassic Argentinean proteochampsids Tropidosuchus romeri, Chanaresuchus bonapartei and Gualosuchus reigi. A congruent phylogenetic position was found by subsequent analyses (Trotteyn & Ezcurra, 2014; Ezcurra, Desojo & Rauhut, 2015).

Gualosuchus reigi Reig, 1971a

Age. Early Carnian, early Late Triassic (Marsicano et al., 2015).

Locality. Los Chañares type locality, near the mouth of Chañares River, Talampaya National Park, La Rioja Province, Argentina.

Stratigraphic horizon. Lower member of the Chañares Formation (sensu Fiorelli et al., 2013), Ischigualasto-Villa Unión Basin.

Holotype. PULR 01: right half side of the skull without braincase, partial right hemimandible, some presacral vertebrae, left scapula, coracoid, femur, tibia, and fibula.

Referred material. PVL 4576: complete skull and lower jaw, presacral vertebral column, sacrum articulated with the pelvis, complete forelimb without manus, scapula, coracoid, femur, tibia, and fibula (Dilkes & Arcucci, 2012).

Diagnosis. Trotteyn, Arcucci & Raugust (2013: 76) diagnosed Gualosuchus reigi as an archosauriform with skull posteriorly taller and narrower than Proterochampsa, Chanaresuchus bonapartei or Tropidosuchus romeri; oval orbits with dorsoventral major axis; parietals diverge posteriorly; supratemporal fenestra narrow and axially elongated; vertebral zonation noticeable, with cervico-dorsal differentiation; humerus robust and shorter than Chanaresuchus bonapartei; femur shorter than the tibia and fibula, and shorter than Chanaresuchus bonapartei; and dorsal osteoderms in one row over the neural spines, one per vertebra, oval in shape and with a smooth surface.

Remarks. Gualosuchus reigi has been identified since its original description as closely related to its probably sympatric species Chanaresuchus bonapartei (Romer, 1971a; Trotteyn, Arcucci & Raugust, 2013). Recent quantitative phylogenetic analyses have bolstered this hypothesis (Dilkes & Arcucci, 2012; Trotteyn & Ezcurra, 2014; Ezcurra, Desojo & Rauhut, 2015).

Chanaresuchus bonapartei Reig, 1971a

Age. Early Carnian, early Late Triassic (Marsicano et al., 2015).

Locality. Los Chañares type locality, near the mouth of Chañares River, Talampaya National Park, La Rioja Province, Argentina.

Stratigraphic horizon. Lower member of the Chañares Formation (sensu Fiorelli et al., 2013), Ischigualasto-Villa Unión Basin.

Holotype. PULR 07: skull and lower jaw, cervical and dorsal vertebrae and ribs, pelvic girdle, and left femur, tibia and fibula.

Referred material. MCZ 4035: articulated vertebral series up to the third caudal vertebra, scapular and pelvic girdle, and partial forelimbs and hindlimbs; MCZ 4036: partial and in part poorly preserved cranial remains and postcranial materials of two additional individuals; MCZ 4037: skull and presacral column; MCZ 4038: slab containing remains of a nearly completely disarticulated skeleton; MCZ 4039: well-preserved left half of a small skull;PVL 4575: partial skull, right hemimandible, cervical, dorsal, sacral, and caudal vertebrae, right scapula and coracoid, right humerus, radius, and ulna, pelvic girdle, and both femora and tibiae; PVL 4586: skull and lower jaw; PVL 4647: partial skull; PVL 4676: partial skull; and PVL 6244: partial postcranium.

Diagnosis. Trotteyn, Arcucci & Raugust (2013: 70) diagnosed Chanaresuchus bonapartei as a proterochampsian with the following unique combination of character-states (autapomorphy indicated with an asterisk): skull long and low, broad posteriorly; slit-like external nares placed close together dorsally some distance back from the tip of the snout; antorbital fenestra small; parietals swing sharply outwards posteriorly above supratemporal fenestrae, towards their meeting with the squamosals; suspensorium far back of occiput with lateral fenestra elongated anteroposteriorly; elongate choanae partially covered below by a secondary palate; long and narrow interpterygoid vacuity, exposing a slender parasphenoid rostrum; and osteoderms wedge-shaped, narrow anteriorly and broader posteriorly*.

Remarks. Chanaresuchus bonapartei is the best-known proterochampsid based on both quantity and quality of the preserved specimens. The anatomy of the species was described by Romer (1971a) and Romer (1972b). Chanaresuchus bonapartei has been used to represent proterochampsid morphology in previous phylogenetic analyses (e.g., Ezcurra, Lecuona & Martinelli, 2010; Desojo, Ezcurra & Schultz, 2011; Nesbitt, 2011; Butler et al., 2014a).

Pseudochampsa ischigualastensis (Trotteyn, Martínez & Alcober, 2012)

Age. Late Carnian–earliest Norian, early Late Triassic (Rogers et al., 1993; Furin et al., 2006; Martínez et al., 2011).

Locality. Valle Pintado, Ischigualasto Provincial Park, San Juan Province, Argentina (Trotteyn, Martínez & Alcober, 2012).

Stratigraphic horizon. Cancha de Bochas Member, Ischigualasto Formation, Ischigualasto-Villa Unión Basin (Trotteyn, Martínez & Alcober, 2012).

Holotype. PVSJ 567: fairly complete, articulated skeleton including skull with fully occluded mandible, complete vertebral series lacking the distal half of the tail, several cervical and dorsal ribs, some haemal arches, some gastralia, pectoral girdle, both partial humeri, partial pelvic girdle, both femora, tibiae, fibulae, tarsals, and pes.

Diagnosis. Pseudochampsa ischigualastensis is distinguished from other proterochampsids, including Chanaresuchus bonapartei, on the basis of the following unique combination of character-states: basicranium transversely broad (basal tubera width/parabasisphenoidal complex axial length ratio = 0.31) and with transversely oriented basal tubera; paroccipital processes with dorsoventrally expanded distal end; lower jaws without retroarticular process; caudal vertebrae with a median longitudinal groove on the ventral surface of the centrum, and pre- and postzygapophyses strongly divergent from the median line; astragalus lacking foramina on the posterior groove; and osteoderms with an ornamentation consisting only of a longitudinal groove (Trotteyn & Ezcurra, 2014: 4).

Remarks. Trotteyn, Martínez & Alcober (2012) erected and briefly described the new species “Chanaresuchusischigualastensis on the basis of a fairly complete, articulated skeleton. Trotteyn & Haro (2012) described in detail the braincase of the species and found a monophyletic Chanaresuchus in a quantitative phylogenetic analysis that sampled only braincase characters. Trotteyn & Ezcurra (2014) described in detail the entire anatomy of “Chanaresuchusischigualastensis and included it for the first time in a phylogenetic analysis sampling the entire anatomy of the terminals. These authors did not find unequivocal evidence for the monophyly of Chanaresuchus and, as a result, erected the new genus Pseudochampsa for the species, resulting in the new combination Pseudochampsa ischigualastensis. More recently, Ezcurra, Desojo & Rauhut (2015) found Pseudochampsa ischigualastensis and Gualosuchus reigi in a polytomy together with a clade composed of Chanaresuchus bonapartei and Rhadinosuchus gracilis, thus supporting the non-monophyly of the genus Chanaresuchus (sensu Trotteyn, Martínez & Alcober, 2012).

Rhadinosuchus gracilis Huene, 1938

Age. Late Carnian–earliest Norian, early Late Triassic (Rogers et al., 1993; Langer, 2005; Furin et al., 2006; Martínez et al., 2011).

Locality. Quarry 17 of the Sanga 6 or ‘Zahn Sanga’, São José, Rio Grande so Sul State, southern Brazil (Ezcurra, Desojo & Rauhut, 2015).

Stratigraphic horizon. Alemoa Member, Santa Maria Sequence 2, Hyperodapedon AZ, Rosário do Sul Group, Paraná Basin (Ezcurra, Desojo & Rauhut, 2015).

Holotype. BSPG AS XXV 50, 51: partial skull and postcranium originally preserved in two blocks of red mudstone. The skull includes both premaxillae and dentaries, right maxilla, nasal, lacrimal and anterior tip of frontal, left jugal, quadratojugal, opisthotic, exoccipital, prootic, and splenial. The postcranium is represented by a posterior cervical centrum, two partial cervical ribs, several gastralia, two dorsal osteoderms, and a probable left metatarsal II. In addition, a possible partial neural arch of the axis and an indeterminate bone are preserved in the main block (Ezcurra, Desojo & Rauhut, 2015).

Diagnosis. Rhadinosuchus gracilis is a proterochampsian distinguished from other basal archosauriforms by the following combination of character-states (autapomorphy indicated with an asterisk): maxilla with a dorsoventrally low antorbital fossa on the horizontal process; nasal with an anteroposteriorly elongated narial fossa and strongly ornamented dorsal surface composed of mainly longitudinally oriented ridges; lacrimal with a very well anteroposteriorly developed antorbital fossa on the ventral process; and dentary with a large, anterodorsally opening foramen on the anterior surface*; and more than 22 dentary tooth positions (Ezcurra, Desojo & Rauhut, 2015: 394).

Remarks. Rhadinosuchus gracilis was the first described proterochampsid but was originally interpreted as a pseudosuchian by Huene (1938). Subsequently, different authors proposed several alternative phylogenetic positions for the species (e.g., Romer, 1945; Romer, 1956; Romer, 1966; Hoffstetter, 1955; Kuhn, 1961; Reig, 1961; Reig, 1970; Bonaparte, 1970), but, in most cases, they agreed that it was an archosaur closely related to Cerritosaurus binsfeldi (see Ezcurra, Desojo & Rauhut, 2015). Indeed, Hoffstetter (1955) considered that Rhadinosuchus gracilis was a probable subjective senior synonym of Cerritosaurus binsfeldi, but this hypothesis was dismissed by other authors (Huene, 1956; Reig, 1970; Bonaparte, 1971) and more recently refutted by Ezcurra, Desojo & Rauhut (2015). After the original descriptions of Chanaresuchus bonapartei and Gualosuchus reigi (Romer, 1971a; Romer, 1972b), Romer (1972a) proposed that Rhadinosuchus gracilis was a member of the family Proterochampsidae, together with the former species and Proterochampsa barrionuevoi and Cerritosaurus binsfeldi. However, this interpretation was not followed by other authors (Sill, 1974; Krebs, 1976). The idea of Rhadinosuchus gracilis as a proterochampsid was readopted by Kischlat & Schultz (1999) and Kischlat (2000), and followed by recent authors (e.g., Dilkes & Arcucci, 2012; Raugust, Lacerda & Schultz, 2013; Trotteyn, Arcucci & Raugust, 2013; Trotteyn & Ezcurra, 2014). More recently, Ezcurra, Desojo & Rauhut (2015) redescribed in detail the holotype and only known specimen of Rhadinosuchus gracilis and included it for the first time in a quantitative phylogenetic analysis. These authors found this species as more closely related to Chanaresuchus bonapartei than to other proterochampsids.

Tarjadia ruthae Arcucci & Marsicano, 1998

Age. Late Ladinian, late Middle Triassic (Marsicano et al., 2015).

Localities. Big bend of the Gualo River, near Agua Escondida (type locality), and Río Chañares, 1.5 kilometres to the north of the Chañares type locality, Talampaya National Park, La Rioja Province, Argentina (Arcucci & Marsicano, 1998).

Stratigraphic horizon. Lowermost levels (0–5 metres) of the lower member of the Chañares Formation (sensu Fiorelli et al., 2013), Ischigualasto-Villa Unión Basin.

Holotype. PULR 063: several dorsal osteoderms and partial vertebrae.

Referred material. MCZ 9319: partial skull roof, including frontals, postfrontal and parietals, supraoccipital, posterior end of the left surangular, and a fragment of dorsal osteoderm; MCZ 4076: posterior end of the right hemimandible, some vertebral fragments, and four dorsal osteoderms; and MCZ 4077: partial right femur and partial dorsal osteoderms.

Emended diagnosis. Tarjadia ruthae is a basal archosauriform that differs from other archosauromorphs by the following combination of features (autapomorphy indicated with an asterisk): dorsoventrally thick skull roof and ornamented by deep pits and grooves of random arrangment*; postfrontal bone present; supraoccipital without median vertical peg; surangular with a strongly laterally developed shelf on the dorsolateral surface of the bone; dorsal vertebrae with a moderately transversely compressed centrum at mid-length; and femur with a poorly developed fourth trochanter.

Remarks. Arcucci & Marsicano (1998) described the remains of a new putative archosaur from the Middle Triassic of Argentina that was named Tarjadia ruthae. The phylogenetic affinities of this new genus and species remained enigmatic until the description of Archeopelta arborensis from coeval beds of southern Brazil. Desojo, Ezcurra & Schultz (2011) proposed that Tarjadia ruthae and Archeopelta arborensis were closely related to each other and also to the North American Late Triassic species Doswellia kaltenbachi, as members of the family Doswelliidae. Desojo, Ezcurra & Schultz (2011) found doswelliids as non-archosaurian archosauriforms more crownwards than Proterosuchus spp., Erythrosuchus africanus, Euparkeria capensis and Chanaresuchus bonapartei.

Arcucci & Marsicano (1998) identified the preserved cranial occipital region of MCZ 9319 as composed of the supraoccipital and the paroccipital processes of the opisthotics. However, the ventral margin of this fragment of skull was originally misinterpreted as dorsal and the dorsal as ventral, and the putative opisthotics are actually the posteroventral processes of the parietals (MCZ 9319). Furthermore, an additional referred specimen of Tarjadia ruthae (MCZ 4077) was identified in the collection of the MCZ.

Archeopelta arborensis Desojo, Ezcurra & Schultz, 2011

Age. Ladinian–early Carnian, late Middle–early Late Triassic (Langer et al., 2007; Desojo, Ezcurra & Schultz, 2011; Philipp et al., 2013; Marsicano et al., 2015).

Locality. Sanga da Árvore (Baum Sanga), Xiniquá region, São Pedro do Sul, Rio Grande do Sul State, Brazil (Desojo, Ezcurra & Schultz, 2011).

Stratigraphic horizon. Santa Maria 1 Sequence, Dinodontosaurus AZ (Desojo, Ezcurra & Schultz, 2011).

Holotype. CPEZ-239a: basicranium, a series of 13 dorsal vertebrae, three dorsal neural spines, two dorsal ribs, two sacral neural arches and their ribs, two sacral or caudal centra, ten paramedian osteoderms, three lateral osteoderms, four undetermined osteoderms, proximal end of right humerus, proximal half of right ulna, right ilium, right ischium, right femur, and proximal end of right tibia (Desojo, Ezcurra & Schultz, 2011).

Diagnosis. Archeopelta arborensis is a doswelliid archosauriform distinguished from other archosauromorphs on the basis of the following combination of features (autapomorphies indicated with an asterisk): basioccipital without occipital neck separating the occipital condyle from the rest of the basicranium*; opistothical paroccipital processes with large and oval fossa on their dorsomedial corner*; suture between the parabasisphenoid and basioccipital interdigitated and V-shaped in ventral view; parabasisphenoid with minute and strongly posteriorly displaced foramina for the internal carotid artery*; dorsal centra without a transverse constriction; first primordial sacral vertebra with circular and extremely large prezygapophyses accounting for 43% of the total length of the neural arch*, and well-developed V-shaped hyposphene*; humerus with a proximomedially orientated head; ilium with base of the iliac blade medially deflected*; femur with strongly transversely expanded distal end representing approximately 150% of the transverse width of the femoral head* (Desojo, Ezcurra & Schultz, 2011: 844).

Remarks. Archeopelta arborensis was named by Desojo, Ezcurra & Schultz (2011) and its description shed new light on the taxonomic content and phylogenetic relationships of Doswelliidae. Lucas, Spielmann & Hunt (2013) suggested that the diagnostic characters of Archeopelta listed by Desojo, Ezcurra & Schultz (2011) do not distinguish the genus from Tarjadia, simply because they pertain to anatomy not known from the fragmentary type material of the latter species. Therefore, Lucas, Spielmann & Hunt (2013) proposed that Archeopelta and Archeopelta arborensis are subjective junior synonyms of Tarjadia and Tarjadia ruthae, respectively. However, this proposal is not followed here because it is based on weak grounds. The occipital surface of the supraoccipital of Tarjadia ruthae is well preserved and clearly lacks a vertical ridge (MCZ 9319), contrasting with the condition in Archeopelta arborensis (Desojo, Ezcurra & Schultz, 2011). The dorsal vertebrae of Tarjadia ruthae are transversely constricted at mid-length (PULR 063), but they are not constricted in Archeopelta arborensis (Desojo, Ezcurra & Schultz, 2011). As a result, the anatomy of Archeopelta arborensis clearly differs from that of Tarjadia ruthae, and they are considered different species. Both species has been scored as independent terminals in the present phylogenetic analysis.

Jaxtasuchus salomoni Schoch & Sues, 2014

Age. Ladinian, late Middle Triassic (Schoch & Sues, 2014).

Localities. Schumann Quarry, Vellberg (Eschenau), east of Schwäbisch Hall, Baden-Württemberg, Germany (type locality). Referred specimens also come from the Kupferzell, Wolpertshausen, Zwingelhausen, Rielingshausen, and Vellberg localities; Baden-Württemberg, Germany (Schoch & Sues, 2014).

Stratigraphic horizon. Upper member of the Lower Keuper, Erfurt Formation (Schoch & Sues, 2014).

Holotype. SMNS 91352A–C: mostly articulated skeleton lacking the skull and cervical vertebrae, recovered as several blocks. SMNS 91352A and B comprise part and counterpart of the anterior portion of the trunk including the forelimbs, and SMNS 91352C preserves the pelvic region, hindlimbs and much of the tail.

Referred material. SMNS 91083: partial, disarticulated anterior portion of a skeleton including both maxillae, probable left postorbital, anterior part of the left nasal, posterior process of left premaxilla, right pterygoid, supraoccipital, basioccipital, both exoccipitals, and left angular; seven transverse rows of osteoderms, each comprising four elements; cervical vertebrae 2–8 and cervical ribs; SMNS 91002: complete forelimb, dorsal osteoderms, and associated femur; SMNS 90500: caudal osteoderms, two vertebrae, and two ribs; SMNS 81868: one dorsal vertebra; SMNS 81906, 90046: two caudal vertebrae; SMNS 81891–81905, 90530–90539: 25 osteoderms; SMNS 90505, dorsal vertebrae, numerous osteoderms, ribs, and possible gastralia; SMNS 90067, 90068: two paramedian osteoderms; SMNS 59403: lateral caudal osteoderm.

Diagnosis. Jaxtasuchus salomoni is distinguished by the following combination of autapomorphies: maxillary teeth with tall, slightly recurved crowns that have prominent vertical ridges along labial and lingual surfaces of tooth crowns and smooth mesial and distal carinae; width of dorsal osteoderms up to 1.2–1.8 times their greatest length; ornamentation most pronounced on dorsal and caudal paramedian osteoderms, comprising prominent ridges and deep pits that are more strongly developed but fewer in number than on comparable osteoderms of Doswellia kaltenbachi; and cervical vertebrae with centra distinctly longer than high, with sixth and seventh cervicals being the longest (Schoch & Sues, 2014: 114).

Remarks. Schoch & Sues (2014) named the new doswelliid archosauriform Jaxtasuchus salomoni and this species currently represents the most completely known Middle Triassic member of the group. Jaxtasuchus salomoni was recovered as more closely related to the North American Doswellia kaltenbachi than to the South American doswelliids (Schoch & Sues, 2014).

Doswellia kaltenbachi Weems, 1980

Age. Carnian, early Late Triassic (Dilkes & Sues, 2009).

Localities. Pit dug for foundation of Doswell sewer plant, 0.4 miles northwest of the confluence of the North Anna River and the Little River, near Doswell, Hanover County, Virginia, USA (type locality); some other localities from the Taylorsville Basin listed by Weems (1980); TMM Localities 31025 and 31098, Texas, USA (Weems, 1980; Long & Murry, 1995).

Stratigraphic horizons. Poor Farm Member, Falling Creek Formation, Doswell Group, Taylorsville Basin (type horizon); and “Pre-Tecovas Horizon” of the Dockum Group, Howard County (Weems, 1980; Long & Murry, 1995).

Holotype. USNM 244214: axial skeleton from seventh cervical through fifth caudal, scattered more posterior caudals, associated ribs, partial pelvic girdle, clavicle, interclavicle, dorsal and lateral armour badly shattered except for an articulated patch from the posterior region (Weems, 1980).

Paratype. USNM 214823: postorbital portion of the skull, postdentary bones of the mandible, second through fifth cervicals, cervical ribs, nuchal armour, cervical osteoderms, and the distal end of a ?tibia (probably from the same individual as the holotype) (Weems, 1980).

Referred material. USNM 25840: two presacral vertebrae; USNM 437574: isolated right jugal; USNM 186989: one cervical vertebra, one posterior dorsal vertebra, left dentary and femur and some osteoderms; USNM 244215: anterior dorsal vertebral centrum; TMM 31025-64: seven dorsal vertebrae; TMM 31025-152: several osteoderms; TMM 31025-153: some osteoderms; TMM 31098-45: much of disarticulated dorsal armour and a single cervical vertebra (Weems, 1980; Long & Murry, 1995; Dilkes & Sues, 2009).

Diagnosis. Dilkes & Sues (2009: 59) diagnosed Doswellia kaltenbachi as an archosauromorph diapsid characterized by the following autapomorphies: elongate diapophyses of dorsal vertebrae with ventral concave and rugose surfaces for articulation with elongate capitulum of dorsal ribs; sharply angled cervical and anterior dorsal ribs; abrupt change in cross-sectional shape of rib cage from narrow to wide between anterior and posterior dorsal vertebrae; extensive series of osteoderms forming transverse rows from back of skull to at least base of tail and including at least five longitudinal rows on each side of vertebral column in posterior dorsal region; ilium with laterally deflected dorsal blade. In addition, Dilkes & Sues (2009: 59) proposed that Doswellia kaltenbachi is also distinguished by the following unique combination of features: prominent occipital peg of supraoccipital that projects over dorsal rim of foramen magnum; euryapsid construction of temporal region with enlarged jugal below supratemporal fenestra; absence of postparietals, tabulars, and postfrontals; small elliptical supratemporal fenestra that does not reach occipital margin; squamosals with posteriorly directed “horn-like” processes; elongate convex dorsal end of quadrate that fits into elongate ventral groove on squamosal; step between the flat skull roof and temporal region; absence of lateral mandibular fenestra; teeth with slender, conical crowns lacking carinae; three sacral ribs, the first derived from dorsal region; and a pair of oval articular facets at distal tips of first two caudal ribs.

Remarks. Doswellia kaltenbachi was named by Weems (1980) and currently represents the best-known doswelliid after a detailed redescription conducted by Dilkes & Sues (2009). Weems (1980) originally considered Doswellia kaltenbachi an archosaur, but that it belonged to its own family and even suborder. Weems (1980) also noted similarities between this species and aetosaurs, though he dismissed any close relationship between them. Nevertheless, Bonaparte (1982) referred Doswellia kaltenbachi to the Aetosauria. Benton & Clark (1988) included this species in a quantitative phylogenetic analysis for the first time and found it as the sister-taxon of Proterochampsidae. This result was also recovered by Dilkes & Sues (2009), but Ezcurra, Lecuona & Martinelli (2010) and Desojo, Ezcurra & Schultz (2011) found Doswellia kaltenbachi as more closely related to Archosauria than to proterochampsids.

Parasuchus hislopi (Lydekker, 1885)

Age. Late Carnian–earliest Norian, early Late Triassic (Rogers et al., 1993; Langer, 2005; Furin et al., 2006; Martínez et al., 2011).

Localities. Vicinity of Mutapuram village, Pranhita–Godavari Valley, Telangana (neotype and referred locality), and Rewa Basin Shadol District, Madhya Pradesh, India (Chatterjee, 1978; Kammerer et al., 2015).

Stratigraphic horizons. Lower Maleri (neotype and referred horizon) and Tiki formations (Chatterjee, 1978; Kammerer et al., 2015).

Neotype. ISI R42: skull with lower jaw and articulated postcranium.

Referred material. ISI R43: partial articulated skeleton lacking the forelimbs and the anterior portion of the skull (found associated with the neotype); ISI R44: partial skull (some elements of which are now lost).

Diagnosis. Kammerer et al. (2015: 7) diagnosed Parasuchus hislopi as a species of Parasuchus distinguished from Parasuchus bransoni by a relatively low narial eminence with a raised, rugose posterior margin of the naris (a ‘narial rim’); distinguished from Parasuchus angustifrons by the absence of paired depressions on the anterior portion of the nasals; and tentatively distinguished from Parasuchus magnoculus by the posterior confluence of the raised margins of the nares.

Remarks. Parasuchus hislopi was originally erected by Lydekker (1885) on the basis of a specimen that is currently considered non-diagnostic (Chatterjee, 1978). A neotype for Parasuchus hislopi (ISI R42) was subsequently designated (Chatterjee, 2001), and Chatterjee (1978) described in detail the available specimens of the species. More recently, Kammerer et al. (2015) revised the taxonomy of basal phytosaurs and concluded that Parasuchus hislopi was a valid species, unlike some previous authors (e.g., Gregory, 1962; Westphal, 1976; Hunt & Lucas, 1991; Long & Murry, 1995), and Parasuchus was a subjective senior synonym of Paleorhinus and Arganarhinus, in agreement with Lucas, Heckert & Rinehart (2007). Parasuchus hislopi has been usually considered one of the most basal known phytosaurs and this hypothesis has been recently supported by quantitative phylogenetic analyses (e.g., Kammerer et al., 2015).

Parasuchus angustifrons (Kuhn, 1936)

Age. Late Carnian, early Late Triassic (Butler et al., 2014b).

Locality. Bed 9 of the Ebrach quarry, Bamberg district, Upper Franconia region of northern Bavaria, Germany (Kuhn, 1933; Kuhn, 1936; Butler et al., 2014b).

Stratigraphic horizon. Blasensandstein of the Sandsteinkeuper, laterally equivalent to the Hassberge Formation of the Middle Keuper (Kuhn, 1933; Kuhn, 1936; Butler et al., 2014b).

Holotype. BSPG 1931 X 502: skull missing the anterior portions of the premaxillae.

Diagnosis. Parasuchus angustifrons is characterized by the following autapomorphies: stepped lateral rim of external naris that is strongly swollen and rugose at posterior end; paired depressions on the anterior portions of the nasals (immediately posterior to the external nares) and anterior portions of the frontals; foramen in ectopterygoid enlarged and subcircular in outline; suborbital foramen elongate and boomerang-shaped; and large postparietal foramen at junction between supraoccipital and parietal (Butler et al., 2014b: 8).

Remarks. Kuhn (1936) erected the new species “Francosuchusangustifrons based on a partial, well-preserved skull. Subsequently, this species was transferred to the genus “Paleorhinus” and its taxonomic validity was questioned (Gregory, 1962; Hunt & Lucas, 1991; Long & Murry, 1995). Butler et al. (2014b) revisited the taxonomy of the Bavarian phytosaurs and concluded that “Paleorhinusangustifrons was a valid species. Kammerer et al. (2015) provided evidence that “Paleorhinus” is a subjective junior synonym of Parasuchus, resulting in the new combination Parasuchus angustifrons. The skull of Parasuchus angustifrons is very well preserved, though somewhat dorsoventrally compressed, and exposes informative features of the palate that are not usually visible or preserved in other basal phytosaurs (BSPG 1931 X 502).

Nicrosaurus kapffi (Meyer, 1860)

Age. Norian, Late Triassic (Hungerbühler, 1998).

Localities. Probably from Heslacher Wand, Stuttgart-Heslach, Baden-Württemberg, Germany (type locality); central Wüttemberg Heslach, Kaltental, Gaisburg, Backnang, and (probably) Degerloch villages on the periphery of Stuttgart and Sindelfingen, Baden-Württemberg, Germany (Hungerbühler, 1998).

Stratigraphic horizon. Löwenstein Formation (Hungerbühler, 1998).

Lectotype. SMNS 4060 and SMNS uncat. no. 15: snout fragment and anterior half of lower jaw (Hungerbühler, 1998).

Paralectotype. SMNS 54708: anterior half of left premaxilla (Hungerbühler, 1998).

Referred material. Multiple specimens described and/or listed by Huene (1923) and Hungerbühler (1998), and housed in the palaeontological collections of the SMNS, NHMUK PV and GPIT.

Diagnosis. Hungerbühler (1998: 41) distinguished Nicrosaurus kapffi from other phytosaurs by the following combination of features: continuous prenarial crest from the external naris to the end of the downturned tip of the snout; and prenarial crest straight or convex at about the level of the skull roof.

Remarks. Nicrosaurus kapffi has a long, complicated taxonomic history that has been summarized by Hungerbühler (1998). The species has been described by Huene (1923), and its cranial anatomy was described in detail by Hungerbühler (1998) and Hungerbühler (2000).

Smilosuchus spp.

Age. Early–middle Norian, Late Triassic (Irmis et al., 2011).

Occurrence. Chinle and Tecovas formations, Arizona and Texas, USA (Long & Murry, 1995).

Species. Smilosuchus gregorii (Camp, 1930), Smilosuchus adamanensis (Camp, 1930), and Smilosuchus lithodendrorum (Camp, 1930) (sensu Stocker, 2010).

Material. Several skulls and postcrania listed by Long & Murry (1995: 227, 299) and housed in the palaeontological collections of the UCMP, USNM, AMNH, UMMP and PPHM.

Synapomorphies. Stocker (2010) found the following synapomorphies for the genus Smilosuchus: ventral margin of squamosal gently sloping anteroventrally from posterior edge of posterior process to opisthotic process; and squamosal fossa extends to posterior edge of squamosal.

Remarks. The species that compose the genus Smilosuchus represent some of the best known phytosaurs and have been long used as representatives of the anatomy of the group, for example regarding hindlimb anatomy (e.g., Parrish, 1986; Sereno & Arcucci, 1990; Sereno, 1991). Smilosuchus gregorii has been used as a species-level representative of phytosaur morphology in previous phylogenetic analyses (e.g., Nesbitt, 2011). The genus has been scored here as a single terminal because the three different species are anatomically conservative and together they provide a fairly complete anatomical record of the skeleton.

Ornithosuchus longidens (Huxley, 1877)

Age. Late Carnian–earliest Norian, early Late Triassic (Rogers et al., 1993; Langer, 2005; Furin et al., 2006; Martínez et al., 2011).

Localities. West (type and referred locality), Spynie, East and Findrassie quarries, Elgin, Scotland, UK (Walker, 1964).

Stratigraphic horizon. Lossiemouth Sandstone Formation (Walker, 1964).

Holotype. EM 1R: large right maxilla.

Referred material. 19–20 specimens listed by Walker (1964: 55–57) and housed in the palaeontological collections of the EM, GSM, MANCH and NHMUK PV.

Diagnosis. Sereno (1991: 12) listed the following autapomorphies that diagnose Ornithosuchus longidens: minor cranial ornamentation; maxilla with free posterior prong; postorbital with strong central horizontal crest; ventral margin of posterior lower jaw concave and elevated; and surangular foramen positioned near surangular-angular suture.

Remarks. See comments in Nesbitt (2011: 22).

Riojasuchus tenuiscepsBonaparte, 1967

Age. Middle Norian, middle Late Triassic (Kent et al., 2014).

Locality. Quebarada de los Jachalleros, La Rioja, Argentina (Bonaparte, 1967; Bonaparte, 1972; Baczko & Desojo, 2016).

Stratigraphic horizon. Upper levels of the Los Colorados Formation, Ischigualasto-Villa Unión Basin (Bonaparte, 1967; Bonaparte, 1972).

Holotype. PVL 3827: complete skull, cervical, dorsal, sacral and caudal vertebrae, scapula, coracoid, humerus, distal portion of the radius and ulna, partial manus, ilium, pubis, femur, tibia, fibula, and nearly complete pes.

Referred material. PVL 3828: nearly complete skull, cervical, dorsal, sacral and caudal vertebrae, scapula, coracoid, humerus, ulna, radius, pubis, ischium, ilium, femur, tibia, fibula, and calcaneum; PVL 2826: cervical, dorsal, sacral and caudal vertebrae, coracoids, scapula fragments, humerus, ulna, radius, ilium, femur, and tibia; and PVL 3814: vertebrae, humerus, and tibia.

Diagnosis. Baczko & Desojo (2016) listed the following autapomorphies that diagnose Riojasuchus tenuisceps: deep antorbital fossa with the anterior and ventral edges almost coinciding with the same edges of the maxilla itself; suborbital fenestra equal in size to the palatine-pterygoid fenestra; and atlantal neural arch bases contact at the midline. These authors distinguished Riojasuchus tenuisceps from all other archosauriforms by the following combination of features: strongly downturned premaxilla; three premaxillary teeth; seven maxillary teeth; second and third teeth on dentary hypertrophied; two-tooth diastema between premaxilla and maxilla; nasal-prefrontal contact absent; jugal with vertical process separating antorbital fenestra from infratemporal fenestra; orbit with ventral point surrounded by V-shaped dorsal processes of the jugal; posterolateral process of the parietals anteriorly inclined greater than 45°; reduced supratemporal fenestra; L-shaped infratemporal fenestra; presence of a palatine-pterygoid fenestra; lower jaws shorter than skull; presence of a first small tooth anterior to the two hypertrophied teeth; anterior end of the dentary dorsally expanded; dentary-splenial symphysis present along one-third of the lower jaw; sharp surangular shelf; presence of a surangular foramen; ventral keel of cervical vertebrae extends ventral to the centrum rims; pubis longer than 70% of femoral length; anterior trochanter (=M. iliofemoralis cranialis insertion) forms a steep margin with the shaft but is completely connected to the shaft; ventral astragalocalcanear articular surface concavoconvex with concavity on astragalus; and metatarsal V without “hooked” proximal end.

It should be noted that the last character-state (metatarsal V without hooked proximal end) occurs in Ornithosuchus longidens (Walker, 1964) but not in Riojasuchus tenuisceps, which possesses a distinctly medially hooked proximal end in the metatarsal V (PVL 3827).

Remarks. See comments in Nesbitt (2011: 22). Baczko & Desojo (2016) recently described in detail the craniodental anatomy, including a digitally reconstructed endocast of the braincase, of Riojasuchus tenuisceps.

Nundasuchus songeaensis Nesbitt et al., 2014

Age. Late Anisian, early Middle Triassic (Nesbitt et al., 2010).

Locality. Z41 locality, between the Ndatira and Njalila rivers, southwestern Tanzania (Nesbitt et al., 2014).

Stratigraphic horizon. Lifua Member, Manda beds, Ruhuhu Basin (Nesbitt et al., 2014).

Holotype. NMT RB48: mostly disarticulated skeleton, including partial right pterygoid, nearly complete right dentary, right splenial, right surangular, isolated teeth, atlas intercentrum, two articulated middle cervical vertebrae, two articulated middle dorsal vertebrae, posterior-most dorsal vertebrae, sacrum and sacral ribs, anterior-most caudal vertebrae, dorsal ribs, gastralia, articulated and isolated paramedian osteoderms, interclavicle, parts of both clavicles, complete left and right scapulae, right coracoid, left humerus, both pubes, both femora, left fibula, proximal and distal portions of left tibia, left astragalus, left calcaneum, left fourth tarsal, left metatarsals (except fourth), distal ends of right metatarsals III, IV, and V, numerous isolated phalanges, partial ungual, and many bone fragments (Nesbitt et al., 2014).

Diagnosis. Nesbitt et al. (2014: 1358) diagnosed Nundasuchus songeaensis on the basis of the following combination of character-states (autapomorphies indicated with an asterisk): multiple anteroposteriorly oriented rows of pterygoid teeth on the palatal process of the pterygoid; anterodorsally oriented grooves on the medial side of the dentary just ventral to dentition*; distinct, lateral expansion of the surangular ridge into a dorsally opening shelf*; paramedian ridges (two total) on the ventral side of the posterior presacral (dorsal) vertebrae*; hyposphene-hypantrum intervertebral articulations in the presacral vertebrae; lateral expansions at the distal margins of the presacral neural spines; two sacral vertebrae; five or six small knobs aligned in an anteroventral row on the lateral side of the coracoid*; short pubic apron; astragalar facet of the calcaneum continuous with a hemicylindrical fibular facet; and anteriorly tapering osteoderms that are arranged in paramedian rows dorsal to the neural spines.

Remarks. Nundasuchus songeaensis was recently named by Nesbitt et al. (2014) and recovered as one of the earliest branching suchians, to the exclusion of gracilisuchids, Revueltosaurus and aetosaurs. Nundasuchus songeaensis possesses an interesting combination of features, with a number of plesiomorphic archosaur character-states that optimize as autapomorphies (Nesbitt et al., 2014).

Turfanosuchus dabanensis Young, 1973c

Age. Anisian, early Middle Triassic (Fröbisch, 2009).

Locality. Taoshuyuanzi, about 30 km northwest of Turfan Basin, Xinjiang Autonomous Region, China (Wu & Russell, 2001).

Stratigraphic horizon. Vertebrate Fossil Bed IV, lower Karamayi Formation (=Kelamayi Formation) (Wu & Russell, 2001).

Holotype. IVPP V3237: partial skeleton (currently mounted in plaster, with the exception of the skull, and several bones reconstructed with plaster).

Emended diagnosis. Turfanosuchus dabanensis is a gracilisuchid archosaur that differs from other archosauromorphs in the following combination of character-states (autapomorphies indicated with an asterisk): nasal with a narrow anterolateral process that bifurcates to receive the postnarial process of premaxilla; maxilla possesses a tall, triangular dorsal process with clear dorsal apex formed by discrete expansion of the posterior end of the horizontal process and broadly contributes to the posteroventral border of the antorbital fenestra in lateral view*; upper temporal bar with a longitudinal, thick ridge on the dorsolateral surface; squamosal with a tapering anteroventral process that subdivides the infratemporal fenestra*; dentary with elongate posteroventral process longer than posterodorsal process; and posterolateral surface of surangular highly concave; and angular excluded by surangular-dentary contact from margin of external mandibular fenestra.

Remarks. Turfanosuchus dabanensis was erected by Young (1973c) and redescribed by Wu & Russell (2001). Nesbitt (2011: 21, 22) discussed the history of the alternative phylogenetic positions that the species had occupied in different phylogenetic analyses and its importance in early archosaur evolution. Butler et al. (2014a) recently recovered Turfanosuchus dabanensis as more closely related to Gracilisuchus stipanicicorum and Yonghesuchus sangbiensis, within the new family Gracilisuchidae.

Gracilisuchus stipanicicorum Romer, 1972c

Age. Early Carnian, early Late Triassic (Marsicano et al., 2015).

Locality. Two kilometres north of the Río Chañares, Los Chañares type locality, near the mouth of Chañares River, Talampaya National Park, La Rioja Province, Argentina (Romer, 1972c).

Stratigraphic horizon. Lower member of the Chañares Formation (sensu Fiorelli et al., 2013), Ischigualasto-Villa Unión Basin (Romer, 1972c).

Holotype. PULR 08: partial skeleton, including fairly complete skull and lower jaw.

Referred material. CRILAR-Pv 490: partial postcranium; MCZ 4116A (in part): partial skull, an incomplete articulated caudal vertebral series, and articulated ischia; MCZ 4117: almost complete and well preserved skull; MCZ 4118, partial skull, articulated cervical series (from axis to cervical 6) and osteoderms, a series of three articulated cervico-dorsal vertebrae, a series of six cervico-dorsal vertebrae articulated with ribs, a dorsal series of at least nine elements; PVL 4597: partial skeleton, including nearly complete skull and lower jaw; PVL 4612, nearly complete skull articulated with the left hemimandible (modified from Lecuona & Desojo, 2011).

Diagnosis. Lecuona & Desojo (2011: 106) diagnosed Gracilisuchus stipanicicorum by the following unique combination of character-states (autapomorphies indicated with an asterisk): large antorbital fenestra occupying approximately 0.3 of the anteroposterior length of the skull table (measured from the anterior end of the premaxilla to the posterior end of the parietals); large antorbital fossa occupying 0.4 of the length of the skull table; presence of a postfrontal and a small postparietal; anterior ramus of squamosal laterally extended; interparietal suture partially obliterated; narrow occipital portion of the parietals; postzygapophyseal facet of the axis horizontal, posteriorly directed, and facing ventrally*; high and vertical anterior border of the axial neural spine*; presence of a ventral longitudinal median keel on axial centrum; poor development of ventral keel on the cervical vertebrae; circular depression on the mid-dorsal region of the neural arch of cervical vertebrae; spine table in posterior cervical vertebrae; lack of a well-defined acetabular surface on the pubis; L-shaped lamina on proximal pubic apron; ischiadic symphysis proximally located*; femur longer than tibia; knob-shaped iliofibular trochanter; and two paramedian osteoderms per vertebra.

Remarks. Romer (1972c) erected and briefly described Gracilisuchus stipanicicorum based on several skeletons collected from the Chañares Formation of northwestern Argentina. The phylogenetic history of the species has been summarized by Nesbitt (2011: 19). Butler et al. (2014a) recovered Gracilisuchus stipanicicorum as a member of the new family Gracilisuchidae, together with the Chinese species Turfanosuchus dabanensis and Yonghesuchus sangbiensis. The pelvic girdle and hindlimb anatomy of the species was redescribed in detail by Lecuona & Desojo (2011).

Aetosauroides scagliai Casamiquela, 1960

Age. Late Carnian–earliest Norian, early Late Triassic (Rogers et al., 1993; Furin et al., 2006; Martínez et al., 2011).

Localities. Hoyada de Ischigualasto, Ischigualasto Provincial Park, San Juan Province, Argentina (type and referred localities); and localities in the Rio Grande do Sul State, Brazil (Casamiquela, 1960; Casamiquela, 1961; Casamiquela, 1967; Desojo & Ezcurra, 2011). The exact stratigraphic provenance of the historical Argentinean specimens described by Casamiquela cannot be determined because of the lack of precise occurrence information. Nevertheless, Martínez et al. (2012) provided a census of a total of 20 specimens of Aetosauroides and determined that they come from the Cancha de Bochas and the lower Valle de la Luna members of the Ischigualasto Formation.

Stratigraphic horizons. Lower levels of the Ischigualasto Formation, Agua de la Peña Group, Ischigualasto-Villa Unión Basin, Argentina, and Santa Maria Sequence 2, Hyperodapedon AZ, Rosário do Sul Group, Paraná Basin, Brazil (Casamiquela, 1960; Casamiquela, 1961; Casamiquela, 1967; Desojo & Ezcurra, 2011).

Holotype. PVL 2073: partial, articulated postcranial skeleton.

Referred material. PVL 2052: natural external mould of the right anterior half of the skull and a portion of the right hemimandible, proximal half of both femora, both tibia, distal end of right fibula, both articulated tarsals and pes, articulated dorsal and ventral carapaces, and some isolated paramedian osteoderms; PVL 2059: partial skeleton, including an incomplete skull and lower jaw; PVL 2091 (holotype of Argentinosuchus bonapartei Casamiquela, 1961): atlas, axis, and third to fifth cervical vertebrae in articulation, with some cervical ribs and osteoderms, a right paramedian osteoderm, two right lateral osteoderms, three ventral osteoderms, three appendicular osteoderms, left humerus, proximal end of left radius and ulna, and seven fragments of osteoderms; PVSJ 326: skull without lower jaw, two posterior or mid-dorsal vertebrae, eight anterior and mid-caudal vertebrae, right humerus, ulna, and radius, right femur, tibia, fragmentary fibula, proximal tarsals, metatarsals I–IV, and three non-ungual phalanges, and one paramedian and one appendicular osteoderm; MCP 13a-b-PV (holotype of “Aetosauroides subsulcatusZacarias, 1982): articulated partial dorsal and ventral carapaces, several isolated paramedian and ventral osteoderms, six complete and articulated middle and posterior dorsal vertebrae, some fragments of dorsal vertebrae and ribs; UFSM 11070a (a single specimen that was collected and housed by three different institutions: MCP, UFRGS, and UFSM): partial braincase, distal half of metatarsal III or IV, one anterior cervical centrum, several dorsal and caudal vertebrae, including a series of four articulated dorsals with associated paramedian osteoderms and dorsal ribs, right calcaneum, several fragments of dorsal ribs, a chevron, and several paramedian osteoderms (housed at MCP), fragmentary two dorsal vertebrae, complete right articulated metacarpus, three non-ungual phalanges, right femur, probable distal end of tibia, dorsal ribs, left calcaneum, several paramedian and appendicular osteoderms (housed at UFRGS), seven dorsal and caudal vertebrae, dorsal ribs, and several paramedian osteoderms associated with rhynchosaur remains (housed at UFSM) (modified from Desojo & Ezcurra, 2011).

Diagnosis. Desojo & Ezcurra (2011: 598) distinguished Aetosauroides scagliai from other known pseudosuchian archosaurs by the following unique combination of apomorphies (autapomorphy indicated with an asterisk): maxilla excluded from the margin of the external naris; ventral margin of dentary convex and without sharp inflexion; tooth crowns with straight distal margin and without constriction between root and crown, denticles, and wear facets; cervical and dorsal centra with oval fossae ventral to the neurocentral suture on the lateral sides of the centra; middle and posterior dorsals with well-developed posterior centrodiapophyseal lamina; and middle and posterior dorsals posterolaterally divergent postzygapophyses, and ratio between the entire length of the postzygapophyses and the width between the distal-most tips of the postzygapophyses equal or lower than 0.75*.

Remarks. Aetosauroides scagliai was originally erected by Casamiquela (1960) and described by the same author in a series of papers (Casamiquela, 1960; Casamiquela, 1961; Casamiquela, 1967). Heckert & Lucas (2000) proposed that Aetosauroides was a subjective junior synonym of Stagonolepis, but this hypothesis was subsequently rejected by Desojo (2005) and Desojo & Ezcurra (2011). Desojo & Ezcurra (2011) also proposed that Aetosauroidessubsulcatus” from Brazil was a subjective junior synonym of Aetosauroides scagliai and extended the geographic distribution of this species to both countries. Aetosauroides scagliai has been recently recovered as the basalmost aetosaur (Desojo, Ezcurra & Kischlat, 2012; Roberto-Da-Silva et al., 2014; Heckert et al., 2015; Parker, 2016). As a result, the combination of well-known anatomy and its basal position within the group makes Aetosauroides scagliai a key representative of aetosaur morphology in phylogenetic analyses.

Batrachotomus kupferzellensis Gower, 1999

Age. Late Ladinian, late Middle Triassic (Gower, 1999; Schoch, 2002).

Locality. Kupferzell, Hohenlohe region of northern Baden-Württemberg (type and referred localities); and Vellberg-Eschenau and Crailsheim, about 10 and 30 km east of Schwäbisch Hall, Baden-Württemberg, Germany (Gower, 1999; Gower & Schoch, 2009).

Stratigraphic horizon. Lower Keuper, Erfurt Formation (Gower, 1999; Gower & Schoch, 2009).

Holotype. SMNS 52970: premaxillae, maxillae, nasals, frontal, postfrontals, parietals, squamosals, postorbitals, jugals, quadrates, dentaries, surangulars, articulars, right lacrimal, right prefrontal, left quadratojugal, left ectopterygoid, left prearticular, isolated teeth, three dorsal, one sacral and three caudal vertebrae, one dorsal osteoderm, right ilium, and a left femur, tibia and fibula (Nesbitt, 2011). A proximal fragmentary right femur catalogued under this number is slightly smaller than the complete right element and questionably belongs to the same individual as the bulk of the holotypic material (Gower & Schoch, 2009).

Referred material. Multiple specimens listed by Gower & Schoch (2009: Appendix I) and housed in the collections of the SMNS and MHI.

Diagnosis. Gower & Schoch (2009: 103, 104) used the following unique combination of features to diagnose Batrachotomus kupferzellensis: short and robust postnasal process of the premaxilla; maxillary palatal process well dorsal to the ventral edge of the bone; kinked anterodorsal maxillary border that contributes to the border of the naris; short ascending process of the maxilla; short and broad dorsal part of the prefrontal; concave anterodorsal edge of the axial neural spine; dorsal vertebrae lacking greatly elongated neural spines; three sacral vertebrae with relatively long, strongly ventrally deflected sacral ribs; and ilium with a subvertical instead of anterodorsally trending (onto anterior iliac process) rugose iliac ridge above the acetabulum, lacking a waisted ilium (sensu Nesbitt, 2005), and lacking coossification among sacral vertebrae.

Remarks. See comments in Nesbitt (2011: 36).

Prestosuchus chiniquensis Huene, 1938

Age. Ladinian–early Carnian, late Middle–early Late Triassic (Langer et al., 2007; Marsicano et al., 2015).

Localities. Weg Sanga (type locality), and Sanga Pascual of the Pinheiros locality, “Posto da Gasolina”, and Sanga da Árvore (Baum Sanga) of the Xiniquá region, Rio Grande do Sul State, Brazil (Huene, 1938; Langer et al., 2007; Mastrantonio et al., 2013).

Stratigraphic horizon. Santa Maria 1 Sequence, Dinodontosaurus AZ (Huene, 1938; Langer et al., 2007; Mastrantonio et al., 2013).

Lectotype. BSPG 1933L 1-3/5-11/28-41/41: splenial, anterior portion of the surangular, anterior portion of the angular, prearticular, right partial maxilla, fragmentary dentary, three incomplete cervical vertebrae, fragmentary ribs, one sacral vertebra, two sacral ribs, five anterior caudal vertebrae with chevron bones, 14 middle and posterior caudal vertebrae, left and right scapulocoracoid, interclavicle and clavicle, distal end of left humerus, proximal and distal ends of right humerus, distal end of radius, fragmentary ulna, one manual phalanx, incomplete ilium, fragmentary ischia, pubes, and complete left hind limb.

Paralectotype. BSPG 1933L/7: articulated vertebral sequence composed of two sacral vertebrae with sacral ribs, incomplete last dorsal and first caudal vertebrae, dorsal portion of the right ilium, and a series of osteoderms articulated with the neural spines.

Referred material. UFRGS 0156-T: complete skull, much of the presacral axial column and articulated osteoderms; UFRGS 0152-T: maxillae, nasals, quadrate, partial quadratojugal, complete braincase, parietal, ectopterygoid, partial pterygoid, jugal, squamosal, anterior portion of the dentary, prearticular, articular, cervical, dorsal, sacral, and caudal vertebrae, osteoderms, scapula, coracoid, humerus, proximal portion of the ulna, complete pelvic girdle, femora, tibia, fibula, calcaneum, pes, chevrons (Nesbitt, 2011); UFRGS-PV-0629-T: partial skeleton (Mastrantonio et al., 2013); MCP-146: a complete pelvic girdle with the last dorsal, two sacral, and three caudal vertebrae preserved in articulation (Bonaparte, 1984; Lacerda et al., 2016); MCZ 4167: partial skeleton (Lacerda et al., 2016); and CPEZ-239b: partial skeleton of a probable juvenile individual (associated with the holotype of Archeopelta arborensis) (Lacerda et al., 2016).

Diagnosis. Two autapomorphies were listed by Desojo & Rauhut (2008): anterior notch between the scapula and coracoid; and a longitudinal ridge on the dorsal surface of the ilium. Nevertheless, a revision of the taxonomy of the Brazilian rauisuchians is currently in preparation (JB Desojo, pers. comm., 2015) and it is necessary to wait for such information to propose an emended diagnosis for the genus and species (Lacerda et al., 2016).

Remarks. See comments in Nesbitt (2011: 33)—for Prestosuchus chiniquensis, UFRGS 0156-T and UFRGS 0152-T—and Lacerda et al. (2016).

Dimorphodon macronyx (Buckland, 1829)

Age. Hettangian–Sinemurian, Early Jurassic (Hallam, 1960).

Occurrence. Lower Lias, Lyme Regis, Dorset, England.

Holotype. NHMUK PV R1034: partial postcranium.

Referred material. NHMUK PV R1035: partial skull and fragmentary postcranium; NHMUK PV R41212: partial skeleton; and several specimens listed by Padian (1983: Table 1) and housed in the collection of the YPM.

Emended diagnosis. Dimorphodon macronyx is a pterosaur distinguished from other archosauromorphs by the following combination of features (autapomorphies indicated with an asterisk): strongly heterodont dentition, with long, slender, trenchant and sharp-pointed anterior teeth and small, closely packed and lancet-shaped posterior teeth*; skull without cresting on the skull roof; external naris that occupies most of the lateral surface of the snout; dentary without a downturned anterior end; tall and slender anterodorsal process of the jugal, forming approximately half of the posterior border of the antorbital fenestra*; and lower jaw with an external mandibular fenestra.

Remarks. See comments in Nesbitt & Hone (2010) and Nesbitt (2011: 43).

Lagerpeton chanarensis Romer, 1971b

Age. Early Carnian, early Late Triassic (Marsicano et al., 2015).

Localities. Approximately 4 kilometres east of the Los Chañares locality, exposures on the northern flank of the north branch of the Chañares River (type locality); and Los Chañares locality, Talampaya National Park, La Rioja Province, Argentina (Sereno & Arcucci, 1994a).

Stratigraphic horizon. Probably lower member of the Chañares Formation (sensu Fiorelli et al., 2013), Ischigualasto-Villa Unión Basin.

Holotype. PULR 06: articulated right hindlimb.

Referred material. PVL 4619: articulated sacrum, pelvis, and partial right and left hindlimbs; PVL 4625: articulated vertebral column including dorsal, sacral, and anterior caudal vertebrae, left pelvis, and left femur; and MCZ 4121: partial right and left femora. Nesbitt (2011) listed a proximal left femur (PVL 5000) among the referred specimens of Lagerpeton chanarensis, but this catalogue number corresponds to a notoungulate mammal (J Powell, pers. comm., 2015).

Diagnosis. Sereno & Arcucci (1994a: 386) diagnosed Lagerpeton chanarensis as a slender-limbed ornithodiran archosaur characterized by: posterior dorsal vertebrae with anterodorsally inclined neural spines; first sacral vertebra with fan-shaped rib extending anterodorsally to the tip of the preacetabular process of the ilium; iliac blade with sinuous dorsal margin; preacetabular process laterally convex with anterior end directed anteromedially; ischial peduncle of ilium recessed; band-shaped eminence passing posterodorsally across lateral surface of postacetabular process; ischium with broad convex ventromedial flange and vertically deep puboischial suture; distal ischial blades horizontal; proximal end of pubis with subtriangular lateral fossa; pubic shaft deflected medially distal to ambiens process; proximal end of femur with flat anteromedial surface; deep femoral head with hook-shaped medial extension; elongate aliform fourth trochanter; distal end of femur with large fibular condyle; astragalus with tongue-shaped posterior ascending process; vascular depression at base of anterior ascending process of astragalus absent; ascending process of the astragalus broadly overlapping tibia and fibula; astragalus and calcaneum co-ossified; calcaneum with flat distal surface canted anteroproximally relative to astragalar distal surface; pedal digit I short relative to digits II–IV, with metatarsal I shorter than all other metatarsals and shorter than phalanx I-1; metatarsal I with laterodistally bevelled proximal end articulating medially with metatarsal II; pedal digit II short relative to digits III and IV with metatarsal II less than two-thirds metatarsal III and only half as long as metatarsal IV; and pedal digit IV and metatarsal IV longer than pedal digit III and metatarsal III, respectively.

Remarks. See comments in Nesbitt (2011: 44).

Marasuchus lilloensis (Romer, 1971b)

Age. Early Carnian, early Late Triassic (Marsicano et al., 2015).

Locality. Southwest part of the Los Chañares locality, Talampaya National Park, La Rioja Province, Argentina (Bonaparte, 1975; Sereno & Arcucci, 1994b).

Stratigraphic horizon. Lower member of the Chañares Formation (sensu Fiorelli et al., 2013), Ischigualasto-Villa Unión Basin.

Holotype. PVL 3871: partial articulated skeleton including the posterior portion of the vertebral column (from the last dorsal vertebra to the 25th caudal vertebra), left scapulocoracoid, humerus, radius, ulna, fragmentary right pelvis, left ilium, left pubis, and partial right and left hindlimbs.

Referred material. PVL 3870: partial skeleton including the maxilla and partial braincase, vertebral column from the atlas to the anterior caudal vertebrae, articulated pelvis and hindlimbs lacking only the distal phalanges and unguals; PVL 3872: partial braincase and articulated vertebral column from the atlas to the ninth presacral vertebra; PVL 4670: articulated anterior caudal vertebrae with chevrons; PVL 4671: articulated anterior caudal vertebrae with chevrons; and PVL 4672: articulated vertebral column from atlas to the 17th presacral vertebra.

Diagnosis. Sereno & Arcucci (1994b: 56) diagnosed Marasuchus lilloensis as a dinosauriform archosaur characterized by: anterodorsally projecting posterior cervical neural spines (presacral vertebrae 6–9); marked fossa ventral to the transverse processes in the posterior cervicals and anterior dorsal vertebrae (presacral vertebrae 6 through 10 or 12); subtriangular neural spines in middle and posterior dorsal vertebrae that contact each other anteriorly and posteriorly; middle caudal centra twice the length of anterior caudal centra; elongate anterior chevrons that are more than three times the length of the first caudal centrum; broad scapular blade; transversely concave distal pubic blade; and transversely narrow fibular articular surface on calcaneum.

Remarks. See comments in Nesbitt (2011: 45, 46).

Lewisuchus admixtus Romer, 1972d

Age. Early Carnian, early Late Triassic (Marsicano et al., 2015).

Locality. Los Chañares locality, Talampaya National Park, La Rioja Province, Argentina (Romer, 1972d).

Stratigraphic horizon. Lower member of the Chañares Formation (sensu Fiorelli et al., 2013), Ischigualasto-Villa Unión Basin.

Holotype. PULR 01: incomplete left and right maxillae with teeth; posterior portion of the skull, including the left laterotemporal region: jugal, postorbital, quadratojugal, squamosal, and quadrate; braincase, comprising supraoccipital, basioccipital, otoccipital, laterosphenoid, parabasisphenoid and prootic; articulated left pterygoid and ectopterygoid; cervical vertebrae from atlas to the seventh vertebra, 11 dorsal vertebrae, nine proximal to middle caudal vertebrae; both scapulocoracoids and humeri; and incomplete tibiae. Bones previously referred to the holotype were later reassigned to indeterminate proterochampsids by Bittencourt et al. (2014), including an isolated dentary and pedal elements. Although this dentary does not match the morphology of a proterochampsid dentary because it is dorsally curved along its entire length, the composition of the hypodigm of Lewisuchus admixtus proposed by Bittencourt et al. (2014) is followed here until more evidence is available.

Diagnosis. Bittencourt et al. (2014: 191) diagnosed Lewisuchus admixtus as a dinosauromorph that can be distinguished by the following combination of features (autapomorphies indicated with an asterisk): extremely elongated skull; supraoccipital nearly horizontal; three foramina posterior to the metotic strut*; anteroposteriorly extending rugose ridge on the middle height of the lateral surface of the axial neural spine*; postzygodiapophyseal lamina of the posterior cervical vertebrae projecting posteriorly to the tip of the postzygapophysis; and the presence of a single row of scutes associated to the distal tip of the cervical and dorsal neural spines.

Remarks. The phylogenetic history of Lewisuchus admixtus has been summarized by Nesbitt (2011: 46). Bittencourt et al. (2014) redescribed in detail the holotype and single known specimen of the species. A recently collected new dinosauriform specimen from the Chañares Formation seems to indicate that Lewisuchus admixtus is a subjective senior synonym of Pseudolagosuchus major (Novas, Agnolín & Ezcurra, 2015), as suggested by Arcucci (1997), Arcucci (1998) and Nesbitt & Hone (2010). Lewisuchus admixtus is scored here solely based on the holotype specimen PULR 01 until a detailed discussion of its synonym with Pseudolagosuchus major based on strong evidence is published.

Silesaurus opolensis Dzik, 2003

Age. Late Carnian, early Late Triassic (Dzik, 2001).

Occurrence. Clay pit in Krasiejów, Opole, Silesia, Poland (Dzik, 2003).

Holotype. ZPAL AbIII/361: dentaries, braincase, pterygoid, frontals, quadrate, surangular, nearly complete presacral column, sacrum, caudal vertebrae, scapulocoracoid, radii, ulnae, complete pelvic girdle and hindlimbs.

Referred material. Multiple specimens listed by Dzik (2003), Dzik & Sulej (2007), and Piechowski & Dzik (2010) and housed in the collection of the ZPAL.

Diagnosis. Dzik (2003: 560) diagnosed Silesaurus opolensis on the basis of the following combination of features: beak on the dentaries; small number of teeth (11–12 in both dentary and maxilla); 25 presacral vertebrae with 9–11 cervicals; elongate, gracile front limbs; and digit I of pes reduced to vestigial metatarsal that probably lacked phalanges. Dzik (2003) originally interpreted that the sacrum of Silesaurus opolensis was composed of four fused vertebrae, but subsequently Dzik & Sulej (2007) reinterpreted the species as having three sacral vertebrae.

Remarks. See comments in Nesbitt (2011: 49).

Heterodontosaurus tucki Crompton & Charig, 1962

Age. Hettangian–Toarcian, Early Jurassic (Norman et al., 2011).

Localities. Behind Tyindini trading store (type locality), and northern slope of Kromspruit Mountain and site 18a of the Kromspruit 9 Farm, Herschel Distrinct, Eastern Cape Province, South Africa (Norman et al., 2011).

Stratigraphic horizons. Clarens Formation and upper part of the Elliot Formation, Stormberg Series (Norman et al., 2011).

Holotype. SAM-K-337: partial skull and lower jaw.

Referred material. SAM-PK-K1332: fairly complete, articulated skeleton; SAM-PK- K1334: partial left maxilla with associated fragments of jugal and lacrimal; and SAM-PK-K10487: partial skull and lower jaw (Norman et al., 2011).

Diagnosis. Norman et al. (2011: 187) listed the following character-states to diagnose Heterodontosaurus tucki (autapomorphies indicated with an asterisk): deep buccal emargination formed by a strongly dorsoventrally compressed and transversely expanded maxillary ridge, which forms the ventral margin of the external antorbital fenestra and is thickened along its lateral margin*; antorbital fossa extends posteriorly to form a channel on the external surface of the jugal*; quadratojugal forms a thin wing that overlaps the entire external surface of the quadrate (contacting the squamosal dorsally and terminating ventrally just above the articular condyle) and contacts the jugal via a narrow bridge of bone*; quadratojugal has a constricted scarf suture with the jugal*; narrow and obliquely orientated ventral jugal projection closely aligned against the lateral surface of the lower jaw*; prominent laterally expanded ‘boss’ on the jugal*; sharply defined curved ridge on the external surface of the postorbital that is continuous with a similar ledge on the dorsolateral margin of the squamosal*; remnants of intracranial pneumatism preserved as pits on the paroccipital process and quadrate, and as sinuses on the jugal boss and anteromedial process of the maxilla*; narrow and deep pterygoid flanges lie close to the medial surface of the lower jaw (forming a slot-like guide with the ventral process of the jugal)*; paroccipital wings perforated by a discrete vascular/neural canal*; basisphenoid flanges are large, oblique and extend medial to the pterygoids and enclose narrow fossae on either side of the ventral midline of the braincase; surangular develops two finger-like rami that form much of the dorsal margin of the coronoid eminence anterior to the jaw joint*; elongate, slot-shaped surangular foramen*; broad depression on the lateral surface of the angular*; premaxillary and dentary caniniforms have fine, blunt, serrations (six per mm) running down their posterior margins; premaxillary caniniform lacks serrations along its anterior edge; dentary caniniform has widely spaced, rounded denticulations running down the upper portion of its anterior edge*; columnar maxillary and dentary teeth have crowns that are only slightly expanded either anteroposteriorly or transversely above the root (the ‘cingulum’ and ‘neck’ at the crown root junction are completely absent)*; labial surface of maxillary crowns possesses three prominent ridges that separate equal-sized, clearly defined excavated regions*; lingual surface of dentary crowns displays a mesially offset principal ridge and crown margins that create subequal adjacent crown areas*; extensive wear facets on the upper and lower dentitions display a warp because successive teeth are worn at differing angles*; axial vertebral column: 21 vertebrae (9 cervical, 12 dorsal)*, sacrum: 6 fused vertebrae*, caudal vertebrae: 34+; prominent epipophyses present on anterior cervical postzygapophyses*, ossified tendons distributed across the neural spines of dorsal and sacral vertebrae only; scapular blade narrow and elongate with expanded distal (extrascapular) portion; humerus with a large deltopectoral crest and large entepicondyle*; humerus lacks a posterior (olecranon) fossa; ulna with prominent olecranon; manus length more than 40% of the combined length of humerus and radius; nine carpal bones; manus digits I–III parallel, digits IV–V reduced in size and divergent; penultimate phalanges of digits II and III more elongated than the proximal phalanges; extensor pits present on the dorsal surface of distal end metacarpals and phalanges; manual unguals strongly recurved, and with prominent flexor tubercles; ilium with a narrow vertical facet on the ischial peduncle that resembles an avian antitrochanter*; prepubic process short and deep, postpubis as long as ischium; obturator process absent; ischial shaft marked by an elongate lateral ridge that is drawn out to form a prominent lateral shelf along the mid-section of the shaft*; femoral greater and anterior trochanters not separated by a cleft; transverse axis of distal femoral articular surface obliquely orientated; fibula reduced and fused to tibia distally*; astragalus and calcaneum fused*; astragalocalcaneum fused to the distal ends of tibia and fibula*; three distal tarsals present but fused to proximal ends of their metatarsals*; and metatarsals I–IV fused together*.

Remarks. Nesbitt (2011: 50) summarized the phylogenetic history of Heterodontosaurus tucki. Santa Luca (1980) and Galton (2014) described the postcranium of this species, and Norman et al. (2011) described in detail its craniodental anatomy. Sereno (2012) added a substantial new amount of information about the anatomy of Heterodontosarus tucki in the context of an overall revision of heterodontosaurids.

Herrerasaurus ischigualastensis Reig, 1963

Age. Late Carnian-earliest Norian, early Late Triassic (Rogers et al., 1993; Furin et al., 2006; Martínez et al., 2011).

Locality. Hoyada de Ischigualasto, Ischigualasto Provincial Park, San Juan Province, Argentina (Reig, 1963; Novas, 1993; Sereno, 1994; Sereno & Novas, 1994; Martínez et al., 2012).

Stratigraphic horizon. Chancha de Bohas Member, lower levels of the Ischigualasto Formation, Agua de la Peña Group, Ischigualasto-Villa Unión Basin (Reig, 1963; Novas, 1993; Sereno, 1994; Sereno & Novas, 1994; Martínez et al., 2012).

Holotype. PVL 2566: dorsal, sacral, and caudal vertebrae, ilium, pubis, ischium, right femur, metatarsals, phalanges and left astragalus.

Referred material. MACN-Pv 18060 (holotype of “Ischisaurus cattoiReig, 1963): partial skeleton, including some cranial bones and elements from all postcranial regions; MCZ 4381: partial pelvic girdle, including both ilia, pubes and proximal end of ischia, and proximal end of left tibia; MCZ 7064: atlas, axis, fragments of at least five dorsal vertebrae, both partial scapulae and coracoids, proximal and distal ends of both humeri, acetabular region of the left ilium, distal halves of both pubes, distal end of the right femur, proximal end of the right tibia and fibula, distal end of the left tibia, and fragments of some pedial phalanges; MLP 61-VIII-2-2: both fairly complete, but poorly preserved pelvic girdle; MLP 61-VIII-2-3: right coracoid, both humeri, fragmentary ulnae, right femur and tibia, and some elements of the pes; PVL 2054: fragments of both pubes and gastralia, most of both femora, tibiae, and fibulae, several metatarsals and phalanges of both pes; PVL 2558a: fragments of both femora, tibiae, and an isolated manual ungual; PVSJ 53 (holotype of “Frenguellisaurus ischigualastensisNovas, 1986): partial skull and complete lower jaw, axis, fragments of cervical and dorsal vertebrae, 25 mostly articulated distal caudal vertebrae, right scapula and fragmentary coracoid, distal end of right humerus and fragment of left humerus, distal ends of both ulnae, proximal end of left ulna and distal end of radius; PVSJ 104: fragmentary pelvic bones, sacral vertebrae and hindlimb elements; PVSJ 373: well preserved articulated skeleton, lacking skull and most cervical and caudal vertebrae; PVSJ 380: right scapula and nearly complete, articulated right carpus and manus; PVSJ 407: nearly complete articulated skeleton with skull and lower jaw; and PVSJ 461: nearly complete, poorly preserved skeleton.

Diagnosis. Novas (1993: 401) diagnosed Herrerasaurus ischigualastensis on the basis of the following combination of character-states: premaxillary-maxillary fenestra posterior to external naris; anterior end of both antorbital fenestra and antorbital fossa semicircular; ventral border of maxilla sinuous, especially at level of jugal articulation; ridge on lateral surface of jugal; upper part of infratemporal fenestra less than one-third as broad as lower part; deeply incised supratemporal fossa that extends across the medial process of postorbital; ventral process of squamosal subquadrate with lateral depression; quadratojugal overlaps posterodorsal face of quadrate; pterygoid ramus of the quadrate with inturned, trough-shaped ventral margin; dentary with slender posterodorsal process with T-shaped cross-section; surangular with forked anterior process for articulation with posterodorsal process of dentary; apices of neural spines of posterior dorsal vertebrae with pronounced lateral borders; internal tuberosity of humerus projecting proximally and separated from the humeral head by deep groove; humeral entepicondyle ridge-like with anterior and posterior depressions; manus 60% of humerus plus radius length; pubis proximally curved and ventrally oriented; lateral margin of the pubis sinuous in anterior view; ischium with posterior border of postacetabular pedicle forming a right angle with dorsal border of ischial shaft; femur with anteroproximal keel and subcircular muscle scar on anterolateral distal shaft; and tibia shorter than femur (tibia length represents 87–91% of femur length).

Remarks. See comments in Nesbitt et al. (2009: 853) and Martínez et al. (2012: 28).

Character sampling and scorings

The character sampling of the phylogenetic analysis was built by combining the character lists of previous phylogenetic analyses focused on non-archosaurian archosauromorphs and basal archosaurs (e.g., Parrish, 1992; Gower & Sennikov, 1996; Gower & Sennikov, 1997; Dilkes, 1998; Ezcurra, Lecuona & Martinelli, 2010; Ezcurra, Scheyer & Butler, 2014; Nesbitt, 2011; Desojo, Ezcurra & Schultz, 2011; Dilkes & Arcucci, 2012; Trotteyn & Ezcurra, 2014; Ezcurra, Desojo & Rauhut, 2015; Pritchard et al., 2015; Nesbitt et al., 2015) after evaluating the independence between characters (repeated or partially non-independent characters were combined with one another). Furthermore, 96 new characters were added. The complete character list includes 600 characters, comprising 309 cranial (51.5%) and 291 postcranial (48.5%) characters. The following 82 characters represent nested sets of homologies and, as a result, were treated as additive (=ordered): 1, 2, 7, 10, 17, 19–21, 28, 29, 36, 40, 42, 50, 54, 66, 71, 75, 76, 122, 127, 146, 153, 156, 157, 171, 176, 177, 187, 202, 221, 227, 263, 266, 279, 283, 324, 327, 331, 337, 345, 351, 352, 354, 361, 365, 370, 377, 379, 398, 410, 424, 430, 435, 446, 448, 454, 458, 460, 463, 472, 478, 482, 483, 489, 490, 504, 510, 516, 529, 537, 546, 552, 556, 557, 567, 569, 571, 574, 581, 582 and 588. Meristic (i.e., characters with character-states represented by numerical ratios rather than qualitatively described features) or count-based characters were discretized using cluster analyses of the raw values for each sampled individual of each terminal (i.e., ranges were included only if there was intraindividual variation for the ratio) in PAST 2.17c (Hammer, Harper & Ryan, 2001) (see Appendix S1). In the resultant meristic trees, two different states were discretized if the distance between them was larger than the complete internal distance of both clusters. In addition, character-states that were separated from each other by less than 5% of the complete range of the sampled raw ratios were merged together.

Table 1:
Sources of scoring for each operational taxonomic unit.
The specimen numbers listed here correspond to specimens studied at first hand.
Terminal Sources of scorings
Petrolacosaurus kansensis Peabody (1952); Reisz (1977) and Reisz (1981)
Acerosodontosaurus piveteaui MNHN 1908-32-57; Currie (1980); Bickelmann, Müller & Reisz (2009)
Youngina capensis BP/1/2459, 3859; GHG K 106, RS 160; NHMUK PV R5481; SAM-PK-K6205, K7578, K7710, K8565; TM 1490, 3603; Broom (1914); Broom (1921); Broom (1922); Gow (1975); Currie (1981); Evans (1987); Smith & Evans (1996); Dilkes (1998); Gardner, Holliday & O’Keefe (2010)
Paliguana whitei AM 3585; Carroll (1975)
Planocephalosaurus robinsonae NHMUK PV R9954–R9969, R9971–R9976; Fraser (1982); Fraser & Walkden (1984); Fraser & Shelton (1988)
Gephyrosaurus bridensis Evans (1980); Evans (1981); Fraser & Shelton (1988)
Cteniogenys sp. Multiple cranial and postcranial bones housed in the NHMUK PV; Evans (1990); Evans (1991)
Simoedosaurus lemoinei MNHN.F.BL9022, BL9425, BL9525, BL9626, BR728, BR1009, BR1013, BR1018, BR1348, BR2075, BR1935, BR10199, BR11715, BR12090, BR12091, BR12108, BR12153, BR12154, BR12179, BR12208, R1381, R1413, R2241, R3313, R3404, R3945, R4014; SMNS 58674, 58594, 58566, 58542, 58564, 58540, 58541, 58577, 58593; Sigogneau-Russell & Russell (1978); Sigogneau-Russell (1981)
Aenigmastropheus parringtoni UMZC T836; Parrington (1956); Ezcurra, Scheyer & Butler (2014)
Protorosaurus speneri BSPG 1995 I 5 (cast of WMsN P47361), 1997 I 12 (cast), 1997 I 13 (cast), AS VII 1207; NHMW 1943I4; USNM 442453 (cast of NMK S 180); SMNS 55387 (cast of Simon/Bartholomäus specimen), 59345 (cast); ZMR MB R2171–R2173 (casts of specimens destroyed probably during WWII); Gottmann-Quesada & Sander (2009)
Amotosaurus rotfeldensis SMNS 50691, 50830, 54783, 54784a, 54784b, 54810, 90540, 90543, 90544, 90552, 90559, 90563, 90564, 90566, 90599–90601, several unnumbered specimens; Fraser & Rieppel (2006)
Macrocnemus bassanii PIMUZ T2472, T4355, T4822; BSPG 1973 I 86 (cast of Besano II); Peyer (1937); Rieppel (1989a)
Tanystropheus longobardicus PIMUZ T2189, T2793, T2817, T2818, T3901; SMNS 54147, 54626, 54628, 54630, 54631, 54632, 54654, 55341, 56289, 59380, 84821, SMNS unnumbered specimen; Wild (1973); Nosotti (2007)
Jesairosaurus lehmani ZAR 06–15; Jalil (1997)
Azendohsaurus madagaskarensis FMNH PR 2751; UA 7-20-99-653, 8-7-98-284, 8-22-97-91, 8-27-98-273, 8-29-97-151, 8-29-97-152, 8-29-97-160, 10603, 10604, UA unnumbered specimens; Flynn et al. (2010); Nesbitt et al. (2015)
Pamelaria dolichotrachela ISI R316–333; Sen (2003)
Trilophosaurus buettneri USNM mounted skeleton; Gregory (1945); Parks (1969); Spielmann et al. (2008)
Noteosuchus colletti AM 3591; Carroll (1976)
Mesosuchus browni SAM-PK-5861, 5882, 6046, 6536, 7416, 7838; Haughton (1921); Carroll (1976); Dilkes (1998)
Howesia browni NHMUK PV R5872 (cast), SAM-PK-5884-5886; Broom (1906); Carroll (1976); Dilkes (1995)
Eohyosaurus wolvaardti SAM-PK-K10159; Butler et al. (2015)
Rhynchosaurus articeps BRLSI M20a, b; NHMUK PV R1236–41; SHYMS 1–7, G3851, G07537; Benton (1990)
Bentonyx sidensis BSPG 3D print of BRSUG 21200; unpublished pictures; Hone & Benton (2008); Langer et al. (2010a)
Eorasaurus olsoni PIN 156/108–110; Sennikov (1997); Ezcurra, Scheyer & Butler (2014)
Prolacertoides jimusarensis IVPP V3233; Young (1973a)
Prolacerta broomi BP/1/471, 2675, 2676, 4504a, 5066, 5375; GHG 431; SAM-PK-K10018, K10797; UMCZ 2003.41R; Gow (1975); Evans (1986); Modesto & Sues (2004)
Kadimakara australiensis holotype QM F6710; Bartholomai (1979)
Kadimakara australiensis combined QM F6676, F6710; Bartholomai (1979)
Boreopricea funerea PIN 3708/1; Tatarinov (1978); Benton & Allen (1997)
Archosaurus rossicus PIN 1100/55; Tatarinov (1960); Ezcurra, Scheyer & Butler (2014)
Proterosuchus fergusi holotype SAM-PK-591; Broom (1903a); Welman (1998); Ezcurra & Butler (2015a)
Proterosuchus fergusi BP/1/3993, 4016, 4224; BSPG 1934 VIII 514; GHG 231, 363; RC 59, 846; SAM-PK-11208, K140, K10603; TM 201; Broom (1903a); Broom (1946); Haughton (1924); Broili & Schröder (1934); Cruickshank (1972), Cruickshank (1979); Welman (1998); Ezcurra & Butler (2015a); Ezcurra & Butler (2015b)
Proterosuchus goweri NMQR 880; Brink (1955); Ezcurra & Butler (2015a)
Proterosuchus alexanderi NMQR 1484; Hoffman (1965); Sereno (1991); Welman (1998); Klembara & Welman (2009); Ezcurra & Butler (2015a)
Chasmatosaurusyuani IVPP V2719, V4067, V36315 (field number V90002); Young (1936); Young (1963); Young (1978)
Chasmatosaurus ultimus IVPP V2301; Young (1958); Liu et al. (2015)
Ankistrodon indicus GSI 2259; Huxley (1865)
Tasmaniosaurus triassicus UTGD 54655; Camp & Banks (1978); Thulborn (1986); Ezcurra (2014)
Exilisuchus tubercularis PIN 4171/25; Ochev (1979)
Blomosuchus georgii PIN 1025/14, 348; Ochev (1978); Sennikov (1992)
Vonhuenia friedrichi PIN 1025/11, 419; Sennikov (1992)
Chasmatosuchus rossicus PIN 2252/381, 3200/212, 217, 472, 2243/167, 2252/384, 386; Huene (1940)
Chasmatosuchus magnus PIN 951/65; Ochev (1979)
Gamosaurus lozovskii PIN 3361/13, 14, 94, 183, 213, 214; Ochev (1979); Sennikov (1995b)
C. magnus+ “G. lozovskii PIN 951/65, 3361/13, 14, 94, 183, 213, 214; Ochev (1979); Sennikov (1995b)
Chasmatosuchusvjushkovi PIN 2394/4; Ochev (1961)
SAM P41754 Long Reef SAM P41754; Kear (2009)
Koilamasuchus gonzalezdiazi MACN-Pv 18119; Bonaparte (1981); Ezcurra, Lecuona & Martinelli (2010)
Kalisuchus rewanensis QM F8998; Thulborn (1979)
Fugusuchus hejiapanensis Unpublished photographs; Cheng (1980); Parrish (1992); Gower & Sennikov (1996)
Sarmatosuchus otschevi PIN 2865/68; Sennikov (1994); Gower & Sennikov (1997)
Guchengosuchus shiguaiensis IVPP V8808; Peng (1991)
Cuyosuchus huenei