Postcranial anatomy of Pissarrachampsa sera (Crocodyliformes, Baurusuchidae) from the Late Cretaceous of Brazil: insights on lifestyle and phylogenetic significance

Ulna.

The right ulna of the holotype of Pissarrachampsa sera is preserved (LPRP/USP 0019), as well as a smaller referred right ulna (LPRP/USP 0740) that corresponds to a juvenile individual. The holotypic ulna is damaged at both ends (Fig. 2). Its maximum proximodistal length is 16.5 cm, and the midshaft mediolateral width is 1.8 cm. The general shape is similar to that of other crocodyliform ulnae, including baurusuchids and other notosuchians (Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Vasconcellos & Carvalho, 2010; Riff & Kellner, 2011; Godoy et al., 2014), but less lateromedially compressed than the gracile ulnae of Araripesuchus tsangatsangana (Turner, 2006). The interosseous space between the articulated ulna and radius is reduced, with nearly no space separating the distal and proximal thirds of both bones shafts. Only in the midshaft region this space is noted, although relatively short if compared with the large space seen in extant crocodylians (Brochu, 1992). This pattern is also seen in other terrestrial fossil crocodyliforms, such as baurusuchids Stratiotosuchus maxhechti (Campos et al., 2001) and Baurusuchus albertoi, as well as Araripesuchus tsangatsangana (Turner, 2006; Nascimento & Zaher, 2010; Riff & Kellner, 2011).

The proximal end of the ulna is craniocaudally expanded compared to both the shaft and distal end, as in other crocodyliforms. Since the proximal end is damaged, the structures of the articular surface with the humerus are not preserved. The olecranon process is severely damaged, hampering the assessment of its morphology. Nevertheless, two expansions are preserved in the proximal end, a cranial process and a conspicuous lateral process. Prior to taphonomic damage, the proximal surface of the lateral process corresponded to the ulnar radiohumeral surface, but the radial facet is still preserved. In proximal view, the ulna-radius articulation forms a sinusoidal contact (Fig. 3A). In caudal view, distal to the olecranon processes, scars are seen for the insertion of the M. triceps brachii tendon (Meers, 2003).

The ulnar shaft is subtriangular in cross-section, similar to that of other baurusuchids and Simosuchus clarki (Sertich & Groenke, 2010) (Nascimento & Zaher, 2010; Riff & Kellner, 2011), differing from the ovoid shaft of Araripesuchus tsangatsangana and Mahajangasuchus insignis (Buckley & Brochu, 1999) (Turner, 2006). The shaft is significantly bowed laterally, resembling the flexure seen in Simosuchus clarki and Chimaerasuchus paradoxus (Wu, Sues & Sun, 1995), different from the faint curvature seen in other baurusuchids and extant forms (Brochu, 1992; Wu & Sues, 1996; Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Vasconcellos & Carvalho, 2010; Riff & Kellner, 2011; Godoy et al., 2014). The cranial surface of the shaft bears a vascular foramen proximal to the midheight, close to the medial margin. On the lateral surface (Figs. 2C–2D), distal to the lateral process of the proximal end, there is a groove for the insertion of M. extensor carpi radialis brevis pars ulnaris (Meers, 2003), which is distally delimited by a ridge, caudal to that groove. This ridge also marks the cranial limit of M. flexor ulnaris, which extends distally to the distal condyle (Meers, 2003). As a whole, this lateral ridge extends proximodistally in an almost straight line, and is similar to the marked ridge seen in other baurusuchids, as Stratiotosuchus maxhechti and Baurusuchus albertoi, but more conspicuous than in Araripesuchus tsangatsangana (Nascimento & Zaher, 2010; Riff & Kellner, 2011). On the caudal surface (Figs. 2E–2F), the limit between M. flexor digitorum longus and M. flexor ulnaris is marked by a caudal ridge on the distal portion of the shaft. In Baurusuchus albertoi and Simosuchus clarki this ridge is lesspronounced, giving a more rounded aspect to the caudal surface of the shaft in these taxa (Nascimento, 2008; Sertich & Groenke, 2010). On the medial surface (Figs. 2G–2H), just distal to the proximal end, there is an ovoid fossa for the insertion of M. pronator quadratus (Meers, 2003). It is deeper than in Simosuchus clarki and Araripesuchus tsangatsangana, but does not extend further distally as in Stratiotosuchus maxhechti (Turner, 2006; Sertich & Groenke, 2010; Riff & Kellner, 2011). Due to the fragmentary condition of the region, the flexor ridge that would mark the limit between M. pronator quadratus and M. flexor digitorum longus pars ulnaris (Meers, 2003) is not preserved. However, the latter muscle extends distally until the cranial oblique process of the distal condyle, as seen by the well-marked scars for its insertion proximal to the process, as seen in many fossil taxa (as Baurusuchus albertoi, Stratiotosuchus maxhechti, Simosuchus clarki) and also in living forms (Brochu, 1992; Riff, 2007; Nascimento, 2008; Sertich & Groenke, 2010).

The distal end of the ulna has a craniocaudal breadth 45% shorter than that of the proximal end. The distal condyle has both cranial and caudal oblique processes turned medially. These processes are about the same size, giving the bone a heart-shaped outline in distal view. The craniolateral process is not completely preserved, due to a damage that also affected the distal surface of the condyle, preventing a precise assessment of the ulnare and radiale articulations. Yet, preserved parts suggest the ulnar articulation with the carpal bones was similar to that of other mesoeucrocodylians, such as Stratiotosuchus maxhechti, in which the cranial oblique process articulates with the radiale and the caudal process articulates with the ulnare (Riff & Kellner, 2011).

Radius.

The right radius is preserved in the holotype of Pissarrachampsa sera (LPRP/USP 0019). The straight proximodistal extension of its slender shaft gives the bone a rod-like shape; which seems to be exaggerated due to the badly preserved proximal and distal ends (Fig. 4). Its maximum proximodistal length is 16 cm, and the midshaft mediolateral width is 1.4 cm. This general shape resembles that of other baurusuchid radii (Nascimento & Zaher, 2010; Vasconcellos & Carvalho, 2010; Godoy et al., 2014), but it is less robust than in Stratiotosuchus maxhechti (Riff & Kellner, 2011) and in extant crocodylians, such as Caiman and Alligator (Brochu, 1992).

The lateral and medial processes of the proximal condyle are not complete but the lateromedial expansion of the proximal end is clear, as in most crocodyliforms (Pol, 2005). The proximal end of the radius is bent cranially at an angle of approximately 25°. In cranial view (Figs. 4A–4B), the radiohumeral articular surface bears a concavity for the articulation of the radial condyle of the humerus. In caudal view (Figs. 4E–4F), part of a crest is seen, adjacent to the lateral process of the proximal condyle. This crest is described by Pol (2005) for Notosuchus terrestris as a thin proximodistal crest and is also present in Simosuchus clarki, as well as in the baurusuchids Stratiotosuchus maxhechti and Baurusuchus albertoi (Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Riff & Kellner, 2011). The ulnar facet is poorly preserved, but it is represented in caudal view by a concavity between the lateral and medial processes. The medial process of the proximal condyle bears, on its medial surface, the scar for the tendon of M. humeroantebrachialis inferior (Figs. 4E–4H). This scar was described by Turner (2006) for Araripesuchus tsangatsangana, and is also present in Simosuchus clarki and Baurusuchus albertoi (Nascimento & Zaher, 2010; Sertich & Groenke, 2010). Caudodistal to this scar, the tubercle for the insertion of M. biceps brachii is seen (Meers, 2003).

The radial shaft is elliptical in cross-section, and marked by scars and ridges for muscle insertions. In cranial view (Figs. 4A–4B), distal to the proximal condyle, the scar for the M. abductor radialis insertion is present, lateral to the tuberosity for the insertion of M. humeroradialis. This scar extends distally to the midlenght of the shaft, as in other notosuchians and living crocodylians (Meers, 2003; Pol, 2005; Turner, 2006; Sertich & Groenke, 2010). More distally, in the midline of the cranial surface, a proximodistally elongated ridge separates the insertions of M. supinator laterally and M. pronator teres, medially, along most of the shaft (Meers, 2003). This ridge is also seen in Baurusuchus albertoi, but less marked than in Stratiotosuchus maxhechti (Nascimento & Zaher, 2010; Riff & Kellner, 2011). The proximodistally long insertions of M. extensor carpi radialis brevis and M. pronator quadratus are better seen, respectively, on the lateral and caudal surfaces (Figs. 4C–4F) (Meers, 2003). A well-developed, proximodistal elongated ridge marks the caudal limit of M. extensor carpi radialis brevis and the lateral limit of M. pronator quadratus (Meers, 2003) at the lateral surface of the distal half of the shaft (Figs. 4C–4D). This ridge extends from the first to the third quarters of the shaft, resembling that of Simosuchus clarki, Baurusuchus albertoi and Aplestosuchus sordidus (Godoy et al., 2014) (Sertich & Groenke, 2010; Nascimento & Zaher, 2010), but is smoother than that of Stratiotosuchus maxhechti (Riff & Kellner, 2011). Also in lateral view, another ridge, in the proximal half of the shaft, separates the insertion extensions of M. extensor carpi radialis brevis and M. abductor radialis (Meers, 2003). This ridge almost reaches the cranial surface, as in other baurusuchids, differing from the pattern seen in Simosuchus clarki, in which the ridge is restricted to the lateral surface (Sertich & Groenke, 2010; Nascimento & Zaher, 2010; Riff & Kellner, 2011; Godoy et al., 2014).

The distal end of the radius is lateromedially expanded and strongly compressed craniocaudally. In distal view, the caudal surface is concave for the articulation with the ulna (Fig. 3B). On the caudal surface of the distal end (Figs. 4E–4F) a small vascular foramen is seen medial to the ulnar articulation concavity. The radiale articulates with the cranial convex surface of the radius. This articulation gives the radial distal end two separate condyles, a more distally extended medial condyle and a lateral one, as seen in Stratiotosuchus maxhechti and Simosuchus clarki (Sertich & Groenke; Riff & Kellner, 2011).

Carpus.

The holotype (LPRP/USP 0019) has both right radiale and ulnare preserved, along with an incomplete right manus (Fig. 5). Only the cranial surfaces of both bones are visible. The pisiform and the distal carpal, which complete the carpus of Crocodylia, are not preserved in Pissarrachampsa sera (Mook, 1921; Nascimento & Zaher, 2010; Sertich & Groenke, 2010). Both radiale and ulnare are elongated bones, a synapomorphy of Crocodylomorpha (Walker, 1970; Clark, 1986; Benton & Clark, 1988). They are very constricted lateromedially and craniocaudally compressed between enlarged proximal and distal ends, as in Simosuchus clarki, Stratiotosuchus maxhechti and Baurusuchus albertoi (Riff, 2007; Nascimento & Zaher, 2010; Sertich & Groenke, 2010), differently from the highly elongated and slender carpals of Araripesuchus tsangatsangana (Turner, 2006).

The proximal surface of the right radiale of Pissarrachampsa sera (holotype, LPRP/USP 0019) is not completely exposed. However, as the preserved medial two-thirds of the surface are concave, this appears to be also the condition of the lacking portion, whereas the lateral third is occupied by a proximally directed convex lateral process. The same pattern is found in Simosuchus clarki, Stratiotosuchus maxhechti, Notosuchus terrestris, Baurusuchus albertoi, Sebecus icaeorhinus, and Yacarerani boliviensis (Novas et al., 2009) (Pol, 2005; Riff, 2007; Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Pol et al., 2012; Leardi et al., 2015). The exposed portion of the proximal surface represents the articulation for the distal end of the radius, as described for Baurusuchus albertoi, Simosuchus clarki, Stratiotosuchus maxhechti and Araripesuchus tsangatsangana (Turner, 2006; Riff, 2007; Nascimento & Zaher, 2010; Sertich & Groenke, 2010). The presence of a marked longitudinal crest in the cranial surface of the radiale has been described for several notosuchians, such as Notosuchus terrestris, Baurusuchus albertoi, Sebecus icaeorhinus, Stratiotosuchus maxhechti, and Yacarerani boliviensis (Pol, 2005; Riff, 2007; Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Pol et al., 2012; Leardi et al., 2015). On the other hand, Turner (2006) describes a “median ridge” in Araripesuchus tsangatsangana, which may correspond to the longitudinal crest. There is no sign of such a crest in the exposed surface of the radiale of Pissarrachampsa sera, but its absence cannot be confirmed as most of the cranial surface of the radiale is embedded in the rock matrix.

Sertich & Groenke (2010) described a prominent pit and a raised rugosity for Simosuchus clarki, which topologically corresponds to the proximal portion of the cranial longitudinal crest in Mahajangasuchus insignis, and represents the insertion of the M. extensor carpi radialis longus (Meers, 2003). The presence of raised scars medial and lateral to this pit is has also been described for Simosuchus clarki, consistent with the origin of the superficial extensor muscles for digits I, II and III (Brochu, 1992; Meers, 2003; Sertich & Groenke, 2010). In Pissarrachampsa sera, despite the lack of the pit, it is possible that the exposed surface of the radiale includes the insertion areas of those extensor muscles, or at least those lateral to the pit in Simosuchus clarki.

The ulnare of Pissarrachampsa sera (holotype, LPRP/USP 0019) seems to be proximodistally shorter than the radiale (Fig. 5), as in Araripesuchus tsangatsangana, Baurusuchus albertoi, Simosuchus clarki, Stratiotosuchus maxhechti, Notosuchus terrestris, Yacarerani boliviensis, and Crocodylia (Mook, 1921; Pol, 2005; Turner, 2006; Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Leardi et al., 2015). Its proximal articular surface is covered by matrix, but its proximal outline seems to be subtriangular, with the apex positioned cranially, as in Simosuchus clarki (Sertich & Groenke, 2010).

The distal end of the ulnare is more expanded than the proximal, as in Notosuchus terrestris, Sichuanosuchus shuhanensis (Wu, Sues & Dong, 1997), Baurusuchus albertoi, Araripesuchus tsangatsangana, Stratiotosuchus maxhechti, Simosuchus clarki, Yacarerani boliviensis, and most non-Crocodylia crocodyliforms (Pol, 2005; Turner, 2006; Riff, 2007; Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Leardi et al., 2015). Yet, the bone is not exposed enough to see if this expansion is symmetrical, as in Simosuchus clarki and Yacarerani boliviensis, or more marked medially, as in Notosuchus terrestris, Stratiotosuchus maxhechti and Baurusuchus albertoi (Leardi et al., 2015)

Manus.

Two right manus are associated to Pissarrachampsa sera, one of the holotype (LPRP/USP 0019) and an isolated one (LPRP/USP 0745). The holotypic right manus (Fig. 5) is composed of five digits: the first includes the metacarpal and the proximal phalanx; the second includes the metacarpal, a poorly preserved proximal phalanx, and the distal phalanx; the third includes the metacarpal and fragments of the medial portions of three phalanges; the last two digits include only the metacarpals. The right manus of LPRP/USP 0745 preserves (albeit partially) all five metacarpals, an incomplete proximal phalanx of the digit I, and a fragment that might represent the proximal phalanx of the digit III. The holotypic manus is better seen in ventral view (Fig. 5B), whereas LPRP/USP 0745 has only its dorsal surface exposed.

From the first to the fourth digits, the metacarpals show a decrease in width and an increase in length (Fig. 5B), as in Baurusuchus albertoi and Stratiotosuchus maxhetchi (Nascimento & Zaher, 2010; Riff & Kellner, 2011). Metacarpal I is the most robust, as in Notosuchus terrestris, Stratiotosuchus maxhechti, Simosuchus clarki, and Yacarerani boliviensis, differing from Crocodylia, in which metacarpal I is similar in robustness to the others (Mook, 1921; Pol, 2005; Sertich & Groenke, 2010; Riff & Kellner, 2011; Leardi et al., 2015). The preserved proximal end of metacarpal V is dorsoventrally flat and lateromedially wide, as in Baurusuchus albertoi, S. maxhetchi, and Yacarerani boliviensis (Nascimento & Zaher, 2010; Riff & Kellner, 2011; Leardi et al., 2015).

All phalanges preserved in the holotype are robust, with a blocky appearance in dorsal and ventral views, with a midlength constriction, also seen in Baurusuchus albertoi, Simosuchus clarki, Stratiotosuchus maxhetchi, Araripesuchus tsangatsangana, and Yacarerani boliviensis (Turner, 2006; Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Riff & Kellner, 2011; Leardi et al., 2015). All manual phalanges of Pissarrachampsa sera that preserve their articular surfaces exhibit medial and lateral condyles, in both the distal and proximal surfaces.

Ilium.

One left ilium is partially preserved for Pissarrachampsa sera (Fig. 6), from a referred specimen (LPRP/USP 0742). It lacks the distal part of the postacetabular process, most of the preacetabular process, and the ventral portion of the acetabular region. The acetabulum is deep, as in Baurusuchus albertoi and Sebecus icaeorhinus, as a result from the strictly lateral orientation of the supraacetabular crest (Nascimento & Zaher, 2010; Pol et al., 2012). On the other hand, the supraacetabular crest of Araripesuchus tsangatsangana projects not only laterally, but also dorsally, which gives a shallower aspect to the acetabulum (Turner, 2006). In some neosuchians and living taxa, the crest is strongly inclined dorsally, giving an accentuated shallow aspect to the acetabulum in lateral view (Leardi, Fiorelli & Gasparini, 2015).

In Pissarrachampsa sera, the morphology of the dorsal surface of the acetabular roof resembles that of Baurusuchus albertoi (Figs. 6A–6B) (Nascimento & Zaher, 2010). In both taxa, the dorsal component of the supraacetabular crest is confluent with the remaining dorsal portion of the bone, extending as a flat horizontal surface, giving the ilium a broad aspect. On the other hand, in Sebecus icaeorhinus, Microsuchus schilleri (Dolgopol de Sáez, 1928), and living forms, such as Caiman latirostris (Daudin, 1802) (MZSP 2137), the supraacetabular crest is not confluent with the rest of the dorsal margin, but has a medial boundary (Pol et al., 2012; Leardi, Fiorelli & Gasparini, 2015). In Sebecus icaeorhinus and Caiman yacare (Daudin, 1802), the dorsal margin is sloped, with the portion corresponding to the supraacetabular crest lying dorsal to the medial portion of the iliac dorsal surface (Nascimento, 2008; Pol et al., 2012). Given the great lateral projection of the supraacetabular crest, the maximum width of the dorsal margin of the ilium of Pissarrachampsa sera is located right above the caudal margin of the acetabular area. The rest of the dorsal surface becomes gradually narrower in the direction of both the pre- and postacetabular processes. Rugosities on the dorsal surface of the supraacetabular crest indicate the area for the attachment of M. iliotibialis 1 and 2 (Romer, 1923; Leardi, Fiorelli & Gasparini, 2015). In Pissarrachampsa sera, most of this surface is rugose, indicating a greater area for the attachment of those muscles.

The proximal portion of the postacetabular process is at least four times dorsoventrally higher than lateromedially wide, and its dorsal margin is slightly caudoventrally oriented. In medial view, it is possible to see the medial expansion of the dorsal portion of the postacetabular process, forming a ridge that extends craniocaudally (Figs. 6C–6D). This ridge marks the dorsal limit of a concave surface on the medial portion of the ilium. Ventrally, this concavity is delimited by a curved ridge, which corresponds to the dorsal part of the articular surface for the second sacral rib (see Pol et al., 2012), and this same morphology is also seen in Baurusuchus albertoi and Sebecus icaeorhinus (Nascimento & Zaher, 2010; Pol et al., 2012). On the other hand, in Theriosuchus pusillus (Owen, 1879) and some extant taxa, such as Caiman yacare and Melanosuchus niger (Spix, 1825), there is no evidence of a supraacetabular process medial crest, which gives a more flattened aspect to the process above the articular surface for the second sacral rib (Wu, Sues & Brinkman, 1996). Baurusuchus albertoi has a total of three sacral vertebrae, with the articulation surface for the third element located in the distal portion of the postacetabular process (Nascimento & Zaher, 2010). Three sacral vertebrae are also found in other baurusuchids, such as Baurusuchus salgadoensis (Carvalho, Campos & Nobre, 2005) (Vasconcellos & Carvalho, 2010) and Aplestosuchus sordidus (Godoy et al., 2014), and there is no evidence of a different condition in Pissarrachampsa sera, although this remains speculative due to the absence of more complete remains.

Ischium.

Both left and right ischia of the holotype of Pissarrachampsa sera (LPRP/USP 0019) are partially preserved, lacking the distal portions of the ischial blade, and of the iliac and pubic peduncles. Despite the incompleteness, the typical crocodyliform ischial morphology is recognizable (Figs. 7A–7B), with a lateromedially constricted ischial blade, a caudal process which would probably contact the ilium, and a cranial process which likely contacted both ilium and pubis (Sertich & Groenke, 2010). The notch between both processes formed the ventral margin of the perforate acetabulum, similar to the condition seen in mesoeucrocodylians such as Chimaerasuchus paradoxus, Mahajangasuchus insignis, Stratiotosuchus maxhechti, and Sebecus icaeorhinus (Wu & Sues, 1996; Buckley & Brochu, 1999; Riff & Kellner, 2011; Pol et al., 2012). The proximal parts of both processes differ in thickness, with a more extended cranial process, as seen in Stratiotosuchus maxhechti and Sebecus icaeorhinus (Riff & Kellner, 2011; Pol et al., 2012). In these two taxa, however, the cranial process expands distally, becoming more robust, an unknown condition for Pissarrachampsa sera.

On the lateral surface of the ischial blade (Figs. 7A–7B), a ridge extends dorsoventrally along its proximal third marking the limits of muscles attached to the ischium. The ischium is very constricted lateromedially, cranial and caudal to this ridge, giving a sharp aspect to its margins. Caudal to the ridge is the area for attachment of both M. flexor tibialis internus pars 3 laterally and M. ischiotrochantericus medially (Hutchinson, 2001a). In the distal portion of the ischial blade, only the cranial margin is constricted, as the dorsoventral ridge becomes confluent with the caudal margin, which becomes more rounded. The constricted cranial margin corresponds to the attachment surface for M. puboischiofemoralis externus pars 3, on the medial surface of the bone (Hutchinson, 2001a; Riff, 2007). In cranial and lateral views, it is possible to see a tubercle on the dorsal portion of the ischial blade, ventral to the cranial process of the ischium. Stratiotosuchus maxhechti bears a similar tubercle, which is interpreted as the attachment point for M. pubioischiotibialis (Riff & Kellner, 2011).

Pubis.

Both pubes are partially preserved (Fig. 7C) in the holotype of Pissarrachampsa sera (LPRP/USP 0019). As is typical for Crocodyliformes, the proximal shaft of the pubis lacks the obturator foramen present in some non-Crocodyliformes Crocodylomorpha, such as Terrestrisuchus gracilis (Crush, 1984). In general, the pubis has a rod-like aspect, as also seen in Baurusuchus albertoi, Stratiotosuchus maxhechti and the protosuchians Protosuchus richardsoni (Brown, 1933) and Orthosuchus stormbergii (Nash, 1968) (Colbert & Mook, 1951; Nash, 1975; Nascimento & Zaher, 2010; Pol et al., 2012). On the other hand, other crocodyliforms such as Araripesuchus tsangatsangana, Notosuchus terrestris, Mahajangasuchus insignis, Theriosuchus pusillus, as well as the living forms, bear an expanded distal pubic end (Brochu, 1992; Wu, Sues & Brinkman, 1996; Buckley & Brochu, 1999; Turner, 2006; Pol, 2005).

Given the incompleteness of the pelvis of Pissarrachampsa sera, the isolation of the pubis from the acetabulum cannot be asserted. Yet, in all Crocodyliformes, except protosuchians, the pubis is excluded from the acetabulum by the cranial process of the ischium, which represents the articulation point for the proximal end of the pubis (Colbert & Mook, 1951). In Pissarrachampsa sera, the partially preserved proximal articulation is lateromedially constricted, and more constricted in its cranial third, giving it a pear-shaped aspect. This lateromedial constriction extends distally along the shaft, as also seen in Stratiotosuchus maxhechti (Riff, 2007). Pissarrachampsa sera and Stratiotosuchus maxhechti also share the proximal pubic shaft bent approximately 30 degrees in relation to the pubic blade. In other notosuchians, such as Araripesuchus tsangatsangana and Simosuchus clarki, and also in the living Crocodylia, such bending is unknown (Turner, 2006; Riff, 2007; Sertich & Groenke, 2010). The pubic blade is craniocaudally constricted in its medial third, which forms the pubic symphysis. Lateral to the laminar symphyseal region, the ischial blade does not show any evidence of the craniocaudal constriction. The attachment area for both M. puboischiofemoralis externus pars 1 and 2 is probably located in the proximal two thirds of the transitional area between the constricted and non-constricted regions of the pubic blade, in the caudal and cranial surfaces respectively (Romer, 1923).

The pubis is a remarkably long element in Pissarrachampsa sera when compared to that of other crocodyliforms. Indeed, even without the distalmost part, the pubic length of Pissarrachampsa sera is 70% of the total length of the femur. This condition is “more similar to that of Stratiotosuchus maxhechti (Riff, 2007), in which this ratio is 80%, than to the condition observed in other crocodyliforms: 25% in Araripesuchus tsangatsangana; 42% in Edentosuchus tienshanensis (Young, 1973); 55% in Sunosuchus junggarensis (Young, 1948); 55% in Mahajangasuchus insignis, and 57% in Caiman yacare (Buckley & Brochu, 1999; Pol et al., 2004; Turner, 2006).

Femur.

There are four preserved femora known for Pissarrachampsa sera. The femoral pair of the holotype (LPRP/USP 0019), as well as two smaller isolated and partially preserved left and right elements (LPRP/USP 0743 and LPRP/USP 0744). The smaller right femur is still in articulation with tibia and fibula, but the following description is based mostly on the holotypic material (Fig. 8), since these are better preserved. The femur is virtually straight in cranial and caudal views, and its proximodistal length is about 24 cm. It is longer than the tibia and or fibula, as seen in most other Mesoeucrocodylia (Leardi, Fiorelli & Gasparini, 2015). In medial and lateral views, the shaft is slightly bowed cranially, and the proximal and distal ends are cranially and caudally curved. The proximal articulation surface is medially inturned, as seen in Baurusuchus albertoi and Stratiotosuchus maxhechti, but not as displaced as in Araripesuchus tsangatsangana (Turner, 2006; Nascimento & Zaher, 2010; Riff & Kellner, 2011). In proximal view (Figs. 8I–8J), the robust articular surface is rounded and rugose at its distal portion, with scars for muscle insertion, whereas the caudolateral extension of the head is slender, as in other baurusuchids and Mariliasuchus amarali (Carvalho & Bertini, 1999) (Nascimento & Zaher, 2010; Riff & Kellner, 2011; Nobre & Carvalho, 2013). At this point, in caudal view (Figs. 8E–8F), there is a proximodistally extensive “greater trochanter” placed laterally, extending cranially and parallel to the “medial proximal crest,” at the caudal most extension of the head (Pol et al., 2012). The “medial proximal crest” turns caudally in Pissarrachampsa sera, and not medially as in Sebecus icaeorhinus (Pol et al., 2012).

In lateral view (Figs. 8G–8H), the proximal part of the femur bears marked depressions and scars for musculature insertion. The scars along the “greater trochanter” correspond to the insertions of M. ischiotrochantericus and M. puboischiofemoralis internus 2, and are also possibly related to the adductor fossa, placed cranially to these muscles insertions (Hutchinson, 2001b; Sertich & Groenke, 2010; Nascimento & Zaher, 2010). In caudal view (Figs. 8E–8F), M. puboischiofemoralis externus (Hutchinson, 2001b) attaches at the “medial proximal crest.” In cranial view (Figs. 8A–8B), the “cranial flange” marks the transition between the proximal femur and the shaft. There are many names for this structure in the literature: anteromedial process (Fiorelli & Calvo, 2007), anterior flange and caudofemoralis flange (Turner, 2006), and cranium-medial crest (Riff, 2007; Nascimento & Zaher, 2010). Although less sharp and prominent than in Simosuchus clarki, this structure is well marked, and bears scars for musculature insertions (Sertich & Groenke, 2010). This condition is similar to that of other baurusuchids and Araripesuchus tsangatsangana, but Microsuchus schilleri and other small notosuchians, such as Mariliasuchus amarali, have a less marked “cranial flange,” which is absent in Sebecus icaeorhinus and Yacarerani boliviensis (Nobre & Carvalho, 2006; Turner, 2006; Nascimento & Zaher, 2010; Riff & Kellner, 2011; Pol et al., 2012; Nobre & Carvalho, 2013; Leardi et al., 2015). In Pissarrachampsa sera, the “cranial flange” divides the femoral shaft in medial and lateral parts. In cranial view (Figs. 8A–8B), the insertion for M. puboischiofemoralis internus 1 is flanked medially by a rugose convexity related to M. caudofemoralis longus (Hutchinson, 2001b). Caudal to that, another smaller rough convexity, also seen in Araripesuchus tsangatsangana, may correspond to the fourth trochanter (Turner, 2006). This corresponds to a shallow proximodistally oriented groove that extends distally as a faint ridge and has scars for the insertion of M. caudofemoralis brevis (Hutchinson, 2001b). It differs from the poorly developed fourth trochanter of Sebecus icaeorhinus, Microsuchus schilleri, and Yacarerani boliviensis and the very prominent structure seen in Simosuchus clarki (Sertich & Groenke, 2010; Pol et al., 2012; Leardi, Fiorelli & Gasparini, 2015; Leardi et al., 2015).

Other muscle scars seen along the shaft, as well as a foramen mediodistal to the cranial flange. Laterodistal to the flange lies the insertion area for the M. iliofemoralis (Hutchinson, 2001b) and distal to the flange, there is an extensive intermuscular line that almost reaches the proximal limit of the intercondylar fossa (Romer, 1956). This corresponds to the M. femorotibialis internus (Hutchinson, 2001b) and its distal most extension forms a longitudinal ridge, named here “femorotibialis ridge.” This intermuscular line does not form a ridge in the juvenile specimen, and is interpreted as an ontogeny-related character. Caiman sp. (LPRP/USP N 0008) also has this intermuscular line, but it does not form a ridge. The presence of this ridge is not clear in other notosuchians, except for Stratiotosuchus maxhecthi and Aplestosuchus sordidus, in which it is smoother than in Pissarrachampsa sera (Riff & Kellner, 2011; Godoy et al., 2014). On the caudal face of the femoral shaft (Figs. 8E–8F), the linea intermuscularis caudalis extends obliquely, from the fourth trochanter to the proximal portion of the lateral condyle, and forms the lateral border of the popliteal fossa. This scar corresponds to the boundary between M. femorotibialis externus, craniomedially, and M. adductor femoris 1 & 2, caudolaterally (Hutchinson, 2001b).

The two distal condyles are well developed, forming the intercondylar fossa cranially and a deep popliteal fossa caudally. The latter is rugose, as in Stratiotosuchus maxhechti, whereas the intercondylar fossa has smoother scars for muscle insertions (Romer, 1956; Riff & Kellner, 2011). The lateral or fibular condyle has a laterodistal concavity, possibly related to the fibular articulation. It is about two times larger than the medial or tibial condyle, which is not as distally expanded as the lateral condyle, a general crocodyliform condition (Sertich & Groenke, 2010; Pol et al., 2012). In lateral view (Figs. 8G–8H), the rugose surface above the lateral condyle makes the insertion of M. gastrocnemius (Brochu, 1992; Sertich & Groenke, 2010). Cranially, the distal portion of the femur has a well developed medial supracondylar ridge, whereas the lateral supracondylar ridge is smoother. This differs from the condition in Sebecus icaeorhinus, which lacks a marked transition from the cranial to the lateral surfaces of the distal femur (Pol et al., 2012). The caudal surface (Figs. 8E–8F) of the distal femur bears both medial and lateral supracondylar ridges (the latter would be the distal extension of the linea intermuscularis caudalis), as well as a popliteal fossa between these (Hutchinson, 2001b; Pol et al., 2012). The medial supracondylar ridge forms a proximodistally oriented crest, above the medial condyle, separating the caudal and lateral surfaces of the distal portions of the femur. The medial facet of the distal portion of the femur is almost flat, cranially bound by the medial supracondylar ridge, whereas in Sebecus icaeorhinus this surface is slightly convex (Pol et al., 2012).

Tibia.

Both tibiae of the holotype (LPRP/USP 0019) are nearly complete, and articulated with the fibulae in their original position (Fig. 9). Additionally, there is a smaller isolated right tibia (LPRP/USP 0741), as well as the additional right tibia in articulation with femur and fibula (LPRP/USP 0744). The shafts of the articulated tibia and fibula are very close to one another (Figs. 9A–9B), as are the radius and ulna. This condition is different from that of modern crocodylians (e.g., Caiman and Melanosuchus) in which this distance is larger. The tibia of Pissarrachampsa sera is similiar in robustness to the tibiae of most crocodyliforms, differing from the more gracile elements of Araripesuchus tsangatsangana and Microsuchus schilleri (Brochu, 1992; Turner, 2006; Leardi, Fiorelli & Gasparini, 2015). The tibia is 18.6 cm long, i.e., 77% the femur’s length, the same ratio of Sebecus icaeorhinus. This differs from other notosuchians, such as the relatively short tibia of other baurusuchids, such as Baurusuchus albertoi and Stratiotosuchus maxhechti, (about 72%) and the elongated bone (82%) of Araripesuchus tsangatsangana (Pol et al., 2012).

The proximal and distal extremities of the tibia are mediolaterally well expanded. The proximal surface is divided into medial and lateral facets (Figs. 9A–9B), which respectively correspond to the articulation areas for the tibial and fibular condyles of the femur. In proximal view, the medial articulation (posteromedial proximal process of the tibia, according to Leardi et al., 2015) has a trapezoid-shape; a pattern also seen in other baurusuchids, such as Stratiotosuchus maxhechti and Baurusuchus albertoi (Nascimento & Zaher, 2010; Riff & Kellner, 2011). The medial articular facet is more protruded relative to the lateral one. The proximal surface of the medial facet forms a gentle concavity, corresponding to the “proximal pit” sensu Brochu (1992), and bears a pronounced deflection toward its caudomedial corner (Fig. 9). This condition is also observed in Sebecus icaeorhinus, which bears a gently protruded medial facet, but differs from Mariliasuchus amarali, Yacarerani boliviensis, and Stratiotosuchus maxhechti, in which that medial portion is weakly pronounced (Pol et al., 2012; Leardi et al., 2015). The latter condition is also present in modern crocodylians (e.g., Caiman, Melanosuchus and Alligator) resulting in equally projected facets. The lateral articular facet is semi-lunar in shape and slightly concave in proximal view. The cranial border is rounded and the caudal tip is somewhat deflected distally. It resembles the pattern of Sebecus icaeorhinus and Yacarerani boliviensis, differing from the weakly projected tip of Mariliasuchus amarali, Araripesuchus tsangatsangana and Stratiotosuchus maxhechti (Turner, 2006; Riff & Kellner, 2011; Pol et al., 2012; Nobre & Carvalho, 2013; Leardi et al., 2015).

Cranially, the proximal expansion of the tibia bears a well-developed tuberosity for the insertion of M. flexor tibialis internus (Figs. 9E–9F). This insertion is proximodistally elongated, as in Araripesuchus tsangatsangana, but it is more sharply raised and closer to the proximal articular surface, a condition more marked than in extant taxa (e.g., Alligator, Caiman and Melanosuchus). Proximolaterally, there is a shallow depression related to the attachment of the internal lateral ligament (Figs. 9E–9F), as in Alligator mississippiensis (Daudin, 1802) (Brochu, 1992). Along with this depression, the lateral margin bears an anterolateral straight ridge (anterolateral proximal ridge, according to Leardi et al., 2015), corresponding to the insertion of M. tibialis anterior. The ridge is proximodistally elongated, as in Araripesuchus tsangatsangana, but not Simosuchus clarki, which bears a tuberosity in the corresponding area (Turner, 2006; Sertich & Groenke, 2010). Caudally (Figs. 9A–9B), the lateral and medial articular facets are separated by a small notch, the “fossa flexoria” sensu Hutchinson (2002) or “posterior cleft” sensu Sertich & Groenke (2010). In Pissarrachampsa sera this fossa is more excavated, as in Araripesuchus tsangatsangana and Stratiotosuchus maxhechti, than in Sebecus icaeorhinus, Yacarerani boliviensis, and Alligator mississippiensis (Brochu, 1992; Turner, 2006; Riff & Kellner, 2011; Pol et al., 2012; Leardi et al., 2015).

The tibial shaft is smooth and rounded in cross section, and craniolaterally bowed. This bowing (see character 336 of Leardi, Fiorelli & Gasparini, 2015) can be seen in different degrees within Mesoeucrocodylia. In Pissarrachampsa sera, Baurusuchus albertoi, Stratiotosuchus maxhechti, and Sebecus icaeorhinus the shaft is markedly bowed, differing from the slightly bowed tibia of Yacarerani boliviensis, Simosuchus clarki, and Araripesuchus tsangatsangana, or the straight one in Alligator (Pol et al., 2012; Leardi et al., 2015). There is no distinguished torsion in the tibial shaft of Pissarrachampsa sera. In caudal view (Figs. 9A–9B), it bears a faint ridge for the insertion of M. flexor digitorum longus. This structure is more prominent in other baurusuchids, such as Stratiotosuchus maxhechti and Baurusuchus albertoi, but absent in Araripesuchus tsangatsangana (Turner, 2006; Nascimento & Zaher, 2010; Riff & Kellner, 2011). In extant crocodylians, the longitudinal crest can be marked (e.g., Alligator and Melanosuchus), or slightly prominent (Caiman).

The distal expansion of the tibia is divided inti lateral and medial portions, both contacting the astragalus. The medial portion is distally projected, forming an oblique distal margin relative to the transverse plane. A similar condition is seen in other mesoeucrocodylians, such as Sebecus icaeorhinus, Stratiotosuchus maxhechti, Notosuchus terrestris, Araripesuchus tsangatsangana, and Yacarerani boliviensis (Turner, 2006; Fiorelli & Calvo, 2008; Riff & Kellner, 2011; Pol et al., 2012; Leardi et al., 2015), and it is different from the sub-equally expanded distal tibia of living crocodylians (Alligator and Crocodylus), and also some notosuchians like Simosuchus clarki, Mariliasuchus amarali, and Microsuchus schilleri (Brochu, 1992; Sertich & Groenke, 2010; Nobre & Carvalho, 2013; Leardi, Fiorelli & Gasparini, 2015). In distal view, the tibial surface has a crescentic shape, resembling more the pattern seen in Araripesuchus tsangatsangana and Yacarerani boliviensis, than the “L-shaped” pattern of Sebecus icaeorhinus (Turner, 2006; Pol et al., 2012; Leardi et al., 2015). The craniolateral margin of the distal portion of the tibial expansion is curved, followed by a short and sharp crest that ends caudally at the fibular contact (Fig. 9B, indicated by an arrow). A triangular depression is seen at the caudal surface between the medial and lateral edges of this expansion. First described for Araripesuchus tsangatsangana (Turner, 2006), this structure is well excavated in other mesoeucrocodylians, such as Sebecus icaeorhinus, Stratiotosuchus maxhechti, and Mariliasuchus amarali (Pol et al., 2012; Riff & Kellner, 2011; Nobre & Carvalho, 2013), but relatively shallow in Baurusuchus albertoi and Yacarerani boliviensis (Nascimento & Zaher, 2010; Leardi et al., 2015). Extant crocodylians, such as Caiman, show a clear depression in the same area, but this structure is not triangular. Cranially, close to the medial margin of the distal expansion, there is a protuberance for insertion of M. interosseus cruris. This structure is placed more proximally in extant taxa, slightly developed in Caiman and Melanosuchus, but marked in Alligator (Brochu, 1992). Among Baurusuchidae, both Stratiotosuchus maxhechti and Baurusuchus albertoi bear the same protuberance, although less prominent in the latter (Nascimento & Zaher, 2010; Riff & Kellner, 2011). Craniolaterally, the distal end of the tibia is devoid of the circular depression for the attachment of the medial tibioastragalar ligament, which is clearly seen in Araripesuchus tsangatsangana (Turner, 2006).

Fibula.

Both fibulae of the holotype of Pissarrachampsa sera (LPRP/USP 0019) are virtually complete (Fig. 9) and in articulation with the tibiae. This is also the case for the fibula of LPRP/USP 0744, preserved in articulation with femur and tibia. The fibula of the holotype is 17 cm long, slender and slightly shorter than the tibia. The fibular width corresponds to half that of the tibia, differing from Baurusuchus albertoi, the fibula of which is three times thinner than the tibia (Nascimento & Zaher, 2010). The proximal articular surface is gently concave, with the lateral border more developed than the medial. In proximal view, the fibula is crescentic in shape and the medial margin is slightly notched. In contrast, the proximal fibula of Stratiotosuchus maxhechti is caudally wedged (Riff & Kellner, 2011).

The proximal end of the fibula is lateromedially flat and strongly expanded caudally. The living forms Melanosuchus, Caiman, and Alligator, bear the same caudal expansion for the attachment of the long external lateral ligament (Brochu, 1992), which is also present in baurusuchids such as Stratiotosuchus maxhechti and Baurusuchus albertoi (Nascimento & Zaher, 2010; Riff & Kellner, 2011). Indeed, the shape of the proximal fibular end varies systematically within Crocodyliformes (Turner, 2006). Whereas modern crocodylians, such as Alligator, bear a straight caudal margin, Yacarerani boliviensis, Araripesuchus tsangatsangana, and Araripesuchus gomesii have strongly inflected caudal margin (Turner, 2006; Leardi et al., 2015), baurusuchids have an intermediate condition, with the caudal margin of the proximal head is slightly curved. Proximocranially, there are attachment scars for M. flexor digitorius longus. The lateral iliofibularis trochanter is sharply raised and proximodistally elongated (Figs. 9C–9F), differing from that of Stratiotosuchus maxhechti, Baurusuchus albertoi, Araripesuchus tsangatsangana, and Yacarerani boliviensis, in which the iliofibularis trochanter is shorter and does not reach the proximal edge (Turner, 2006; Nascimento & Zaher, 2010; Riff & Kellner, 2011; Leardi et al., 2015). In extant forms, this trochanter is tubercle-shaped and distant from the proximal edge (Brochu, 1992).

The fibular shaft is almost entirely compressed lateromedially, except in its middle portion, which is elliptical in cross-section. Laterally, the fibular shaft bears faintly developed ridges, as in Baurusuchus albertoi, corresponding to the origin of M. peroneus longus (sensu Brochu, 1992) or M. fibularis longus (sensu Hutchinson, 2002). A different condition is seen in Stratiotosuchus maxhechti, in which that ridge is well developed (Riff, 2007). Among extant crocodylians, both Caiman and Melanosuchus show weakly developed ridges on the lateral surface of the fibular shaft, whereas in Alligator the fibula bears well developed crests and a slightly rugose shaft lateral surface (Brochu, 1992). In medial view, the shaft is mostly smooth and lacks any distinctive muscle scar. However, the caudodistal surface is rugose, revealing scars possibly related to the attachment for M. interosseus cruris, as also observed in Araripesuchus tsangatsangana and Stratiotosuchus maxhechti (Turner, 2006; Riff, 2007). There is a small vascular foramen on the caudal surface near the midshaft. The tibial distal end is enlarged with a triangular distal outline, as in Araripesuchus tsangatsangana and Microsuchus schilleri (see Leardi, Fiorelli & Gasparini, 2015: character 425). As in Alligator, Caiman, and Melanosu“hus, a “dis”al hook” (sensu Brochu, 1992) contacts the tibia and tapers medially. This differs from the condition in Stratiotosuchus maxhechtiand Yacarerani boliviensis, in which the medial end of the distal margin of the tibia is rounded (Riff & Kellner, 2011; Leardi et al., 2015). The contact of the distal hook with the tibia is more proximal then the distal tibial articulation (Fig. 9), and differs from the pattern in Microsuchus schilleri, the distal hook of which contacts the tibia more distally. This hook is absent in Araripesuchus tsangatsangana and Yacarerani boliviensis (Turner, 2006; Leardi et al., 2015).

Tarsus.

Both complete astragali and calcanea are preserved in articulation (Fig. 10) in the holotype of Pissarrachampsa sera (LPRP/USP 0019), although the more distal tarsal bones are not preserved. The best preserved left astragalus and calcaneum are slightly displaced from their original positions. The tarsal morphology of Pissarrachampsa sera is similar to that of other crocodylomorphs with the “crocodile normal” condition, in which the astragalar “peg” fits into the calcaneal “socket” (Chatterjee, 1978; Chatterjee, 1982). In this configuration, the astragalus is fixed in articulation with tibia and the ankle rotation occurs between astragalus and calcaneum (Brochu, 1992).

Proximally, the astragalus bears a concave and laterally elongate surface for articulation with the distal tibia (Figs. 10A–10B). The division of this surface for the reception of medial and lateral condyles of the tibia is weak and both facets are similar in lateromedial extension. These are bounded caudally by a ridge, but this structure is more developed on the lateral region of the medial tibial facet. As in the baurusuchids Baurusuchus albertoi and Stratiotosuchus maxhechti and the sebecid Sebecus icaeorhinus (Riff & Kellner, 2011; Pol et al., 2012), there is no sign of an “astragalar fossa” (Hecht & Tarsitano, 1984). This differs from the morphology of extant taxa, Simosuchus clarki, and Yacarerani boliviensis, in which the fossa is present and well developed (Hecht & Tarsitano, 1984; Brochu, 1992; Sertich & Groenke, 2010; Leardi et al., 2015). The lateral tibial facet is flat, equally developed lateromedially and ends just craniomedial to the fibular facet (Figs. 10A–10D). The lateromedial edge of the lateral tibial facet seems to lack the notch observed in Yacarerani boliviensis, Stratiotosuchus maxhechti, Sebecus icaeorhinus, and Lomasuchus palpebrosus (Gasparini, Chiappe & Fernandez, 1991), but this surface is damaged in both left and right elements (Pol et al., 2012; Leardi et al., 2015). The lateral tibial and fibular articular surfaces are set almost perpendicular to each other, as in other fossil crocodyliforms, such as Simosuchus clarki, Baurusuchus albertoi, Stratiotosuchus maxhechti, Yacarerani boliviensis, and also in extant forms (Hecht & Tarsitano, 1984; Brochu, 1992; Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Riff & Kellner, 2011; Leardi et al., 2015). The medial tibial articular facet is reniform, as in Sebecus icaeorhinus, but more craniocaudally expanded, as in Simosuchus clarki and Yacarerani boliviensis (Sertich & Groenke, 2010; Leardi et al., 2015). The fibular facet is trapezoidal and slightly concave. Distally, the astragalus bears a medial distal roller (Hecht & Tarsitano, 1984) and the calcaneal articulation (Brochu, 1992). The distal roller is elliptical in distal view and extends cranioproximally merging into the craniomedial edge of the tibial facet. The metatarsals are not preserved in articulation with the astragali, but there is a slight depression in the distal surface of the medial distal roller that is probably related to the articulation of both first and second metatarsals, as in Baurusuchus albertoi, Simosuchus clarki, Stratiotosuchus maxhechti, and extant forms (Hecht & Tarsitano, 1984; Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Riff & Kellner, 2011).

The calcaneal articulation is formed by a well developed distolaterally directed peg as in other crocodyliforms. This is divided in two distinct areas, the distal area of articulation (“astragalar trochlea” of Hecht & Tarsitano, 1984) and the lateral articular surface. Yet, the morphology of these facets cannot be accessed due the tight articulation with the calcaneum in both sides. The cranial surface of the astragalus consists of a limited non-articular region (the “anterior hollow” of Hecht & Tarsitano, 1984). This area is more restricted when compared to that of Sebecus icaeorhinus, Simosuchus clarki, and extant forms, but similar to the condition of Baurusuchus albertoi and Stratiotosuchus maxhechti (Hecht & Tarsitano, 1984; Brochu, 1992; Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Riff & Kellner, 2011; Pol et al., 2012). As in Sebecus icaeorhinus, Stratiotosuchus maxhechti, and Simosuchus clarki (Pol et al., 2012; Leardi et al., 2015), the “anterior hollow” does not seem bounded distally and laterally by crests, but its lateralmost surface is somewhat damaged. Distally, the pit for the astragalar-tarsale ligament is located at the anterior hollow, close to the medial distal roller (Brinkman, 1980). The pit is well-developed, as in Yacarerani boliviensis, Simosuchus clarki, Stratiotosuchus maxhechti, and Sebecus icaeorhinus, differing from the reduced depression of Baurusuchus albertoi (Sertich & Groenke, 2010; Nascimento & Zaher, 2010; Riff & Kellner, 2011; Pol et al., 2012; Leardi et al., 2015). The vascular foramina observed in other taxa, such as Baurusuchus albertoi, Stratiotosuchus maxhechti, and Simosuchus clarki (Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Riff & Kellner, 2011), are not present in Pissarrachampsa sera, nor in Sebecus icaeorhinus (Pol et al., 2012).

The calcaneum of Pissarrachampsa sera is robust and mediolaterally developed, as in Yacarerani boliviensis, Baurusuchus albertoi, Stratiotosuchus maxhechti, and Sebecus icaeorhinus, differs from the mediolaterally compressed calcaneum of Araripesuchus tsangatsangana and Uruguaysuchus aznarezi (Rusconi, 1933) (Turner, 2006; Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Riff & Kellner, 2011; Pol et al., 2012; Leardi et al., 2015). It is formed by a cranial body, a socket for the reception of the astragalar peg, and the caudally directed tuber (Brochu, 1992). As in other crocodyliforms, the cranial body in P. sera contacts the astragalus, fibula, and possibly the fourth distal tarsal (Brinkman, 1980; Hecht & Tarsitano, 1984; Brochu, 1992; Sertich & Groenke, 2010; Pol et al., 2012).

The cranial and proximal portions of the cranial body form a well-developed rounded articular surface (a roller) that articulates medially with the astragalus and proximally with the fibula. This morphology is widespread, also seen in living forms and other fossil crocodylians, as Baurusuchus albertoi, Stratiotosuchus maxhechti, Sebecus icaeorhinus, Simosuchus clarki, and Araripesuchus tsangatsangana (Brinkman, 1980; Turner, 2006; Sertich & Groenke, 2010; Nascimento & Zaher, 2010; Riff & Kellner, 2011; Pol et al., 2012). No ridge is present at the articular surface of the roller, which in Simosuchus clarki separates the medial articulation area for the astragalus and the lateral articulation area for the fibula (Sertich & Groenke, 2010). This rounded surface slopes abruptly cranioventrally, forming a distally directed surface, which probably contacted the fourth distal tarsal. In Pissarrachampsa sera, this surface is flat and elliptical in distal view, resembling the condition in Stratiotosuchus maxhechti (Riff & Kellner, 2011). The lateral portion of the cranial body forms a well-developed flat surface that lacks any articular facet. This surface is proximodistally restricted and does not overcome the proximodistal extension of the distal tuber. The medial face of the cranial body forms the calcaneal socket. Most of the morphology of this area is not accessible due the articulation with the astragalus, but a faint medial flange overhangs the calcaneal socket as in Simosuchus clarki (Sertich & Groenke, 2010).

The calcaneal tuber is caudally directed and sub-elliptical in caudal view, as in Baurusuchus albertoi and Stratiotosuchus maxhechti (Nascimento & Zaher, 2010; Riff & Kellner, 2011). The caudal surface of the tuber is orthogonal to the distal facet of the calcaneal condyle, and is deeply concave, forming a slot for attachment of M. gastrocnemius (Brochu, 1992; Leardi et al., 2015). The concavity divides the tuber into well-marked lateral and medial ridges, as in Baurusuchus albertoi, Stratiotosuchus maxhechti, Sebecus icaeorhinus, Araripesuchus tsangatsangana, and Simosuchus clarki (Turner, 2006; Riff & Kellner, 2011; Sertich & Groenke, 2010; Pol et al., 2012). Unlike in Stratiotosuchus maxhechti, there is no transversal ridge separating the caudal surface in proximal and distal areas (Riff & Kellner, 2011). The lateral ridge is shorter than the medial one, as in Simosuchus clarki and Uruguaysuchus aznarezi, whereas in other taxa (Baurusuchus albertoi, Stratiotosuchus maxhechti, Sebecus icaeorhinus) both ridges are equally developed (Sertich & Groenke, 2010; Nascimento & Zaher, 2010; Riff & Kellner, 2011; Pol et al., 2012). The lateral ridge bears a lateral tubercle, as in Yacarerani boliviensis, Sebecus icaeorhinus and Stratiotosuchus maxhechti (Riff & Kellner, 2011; Pol et al., 2012; Leardi et al., 2015). The tubercle extends laterodistally and invades the lateral surface of the calcaneal tuber (Figs. 10E–10F). A well-defined groove flanks the medial side of the calcaneal tuber. This corresponds to the “medial channel” of Hecht & Tarsitano (1984). It expands proximolaterally in a shallow and wide surface that terminates abruptly at the lateral edge of the calcaneum. A lateral groove also separates the distal articular surface of the cranial body from the calcaneum tuber, just medial to the lateral tubercle, as seen in Simosuchus clarki (Sertich & Groenke, 2010).

Pes.

Pissarrachampsa sera has three preserved pedes, the left pes of the holotype (LPRP/USP 0019) and two referred (a left and a right) pedes (LPRP/USP 0739 and LPRP/USP 0746). The holotype pes is represented by four articulated metatarsals (Fig. 11B), whereas LPRP/USP 0739 includes four isolated metatarsals, and LPRP/USP 0746 comprises four partially preserved articulated digits (Fig. 11A). Metatarsal V is not preserved in any of the specimens of Pissarrachampsa sera, following the trend of reduction of that metatarsal towards Crocodylomorpha (Parrish, 1987). Therefore, the four metatarsals preserved in Pissarrachampsa sera constitute the entire number of fully functional pedal digits, as in all living crocodylians and most fossil crocodyliforms (Riff, 2007).

The metatarsals of Pissarrachampsa sera are longer than the metacarpals, as in Baurusuchus albertoi, Araripesuchus tsangatsangana, Stratiotosuchus maxhetchi, Simosuchus clarki and Yacarerani boliviensis (Turner, 2006; Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Riff & Kellner, 2011; Leardi et al., 2015). Moreover, metatarsals II and III are slightly longer than metatarsals I and IV, as in Baurusuchus albertoi and possibly in Yacarerani boliviensis and S. maxhetchi (Nascimento & Zaher, 2010; Riff & Kellner, 2011; Leardi et al., 2015). The proximal articular surfaces of the metatarsals are lateromedially expanded, especially in their lateral margin. As a result, the proximal surface of each metatarsal overlaps the medial portion of the proximal surface of the immediate lateral metatarsal (Fig. 11—LPRP/USP 0746) as in Baurusuchus albertoi, Simosuchus clarki, and Stratiotosuchus maxhetchi (Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Riff & Kellner, 2011). This morphology is different from that of Araripesuchus tsangatsangana, in which a medial expansion of these surfaces underlies the proximal surface of the immediate medial metatarsal, and from Yacarerani boliviensis, in which there is a medial expansion of the surface in each metatarsal that overlaps the immediate medial metatarsal (Turner, 2006; Leardi et al., 2015). The distal articular surfaces are divided by a groove in the medial and lateral condyles, as in Simosuchus clarki, Baurusuchus albertoi and Stratiotosuchus maxhechti (Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Riff & Kellner, 2011).

Only LPRP/USP 0746 preserves articulated phalanges (Fig. 11A), but the phalangeal formula cannot be assessed. The phalanges have a blocky appearance and a constriction between the expanded proximal and distal ends, as in Simosuchus clarki, Baurusuchus albertoi, Stratiotosuchus maxhechti, and Araripesuchus tsangatsangana (Turner, 2006; Nascimento & Zaher, 2010; Sertich & Groenke, 2010; Riff & Kellner, 2011). The proximal phalanges preserved in LPRP/USP 0746 are relatively longer than those preserved in the right manus of the holotype (both hands are similar in size), a pattern described for both Baurusuchus albertoi and Stratiotosuchus maxhechti (Nascimento & Zaher, 2010; Riff & Kellner, 2011). Also, the proximal phalanges preserved in LPRP/USP 0746 are longer than the preserved more distal phalanges, as in Baurusuchus albertoi, Araripesuchus tsangatsangana, and S. maxhetchi (Turner, 2006; Nascimento & Zaher, 2010; Riff & Kellner, 2011).

Aside from the articulated phalanges of LPRP/USP 0746, three disarticulated pedal ungual phalanges were found associated with the holotype skeleton (Fig. 11C). They decrease in size from the first to the third digit, as in Baurusuchus albertoi, Stratiotosuchus maxhechti, Uberabasuchus terrificus and living crocodylians (Müller & Alberch, 1990; Vasconcellos, 2006; Riff, 2007; Nascimento & Zaher, 2010). They form curved claws, with a robust base, and bear foramina in both lateral and medial surfaces, as also present in Baurusuchus albertoi and, possibly, in Araripesuchus tsangatsangana (Turner, 2006; Nascimento, 2008; Nascimento & Zaher, 2010).