Seazzadactylus venieri gen. et sp. nov., a new pterosaur (Diapsida: Pterosauria) from the Upper Triassic (Norian) of northeastern Italy

Locality and geological setting

According to the discoverer, Mr. Umberto Venier, MFSN 21545 was preserved in a loose boulder in the bed of the Seazza Brook (Preone Municipality, Friuli Venezia Giulia Autonomous Region, NE Italy; Fig. S2) at ca. 435 m above the sea level, just upstream of the angle bend in the final tract of the brook before it issues into the Tagliamento River.

The boulder lithology (dark grey laminated dolostone) and the local stratigraphy (Dalla Vecchia, 2012), as well as geomorphologic and topographic constraints, indicate that the specimen comes from the lower member of the Dolomia di Forni Formation (sensu Dalla Vecchia, 1991; see also Dalla Vecchia, 2012), possibly from its lower portion. The fossiliferous portion of the Dolomia di Forni Formation was dated to the late middle to late Norian (Alaunian 3-Sevatian) on the basis of its conodont assemblages (Dalla Vecchia, 2014).

Cranial bones

Many skull elements are preserved and can, because of their disarticulated state, be observed in aspects not visible in articulated skulls (Fig. 3). Unfortunately, a wide fracture crosses the caudal part of the skull and some bones, mainly those of the skull roof, were either lost or incompletely preserved.

Premaxillae. The premaxillae (Fig. 4) are fused but their suture is still evident. Both dorsal and lateral sides of the right premaxilla are exposed, whereas only the dorsal portion of the left one is visible. As exposed, the premaxillae are very narrow and long (18.2 mm long [excluding the apical tooth] and six mm maximum width) and slightly taper rostrally. They are broken anterior to the rostral margin of the external naris. The rostral tip of the joint premaxillae is blunt. The premaxillary body is low in lateral view. The first tooth of the left premaxilla is still in situ and points forwards, whereas four teeth have dropped out of their alveoli. Only two large distal alveoli are fully exposed along the ventral margin of the right premaxilla, because two displaced teeth conceal the mesial alveoli. Teeth occur only in the rostral half of the premaxillary body.

Maxillae. Both maxillae (Fig. 5) show their lateral side, due to the upside-down flipping of the left maxilla. The left maxilla is complete and is 33.2 mm long. The premaxillary process of the right maxilla is rostrally damaged by a fracture and its rostral end is covered by matrix and the displaced left maxillary tooth 8. The maxilla is a triradiate element with slender processes that taper distally to a point. The jugal process is the longest, whereas the premaxillary and the ascending processes are of about the same length (the premaxillary process is 55% of the length of the jugal process). The ascending process slopes caudally at 145° and is slightly arched. It tapers apically to a narrow point and is relatively short; apically, it has a long articular surface along the caudal side, like that for the lacrimal in the reconstruction of the skull of Scaphognathus crassirostris by Wellnhofer (1975b, fig. 34a). A short and deep longitudinal groove on the lateral side of the expanded base of the ascending process (Fig. 5) probably corresponds to the large neurovascular foramen observed there in the maxilla of Preondactylus buffarinii and Caelestiventus hanseni (see Britt et al., 2018). There is no trace of a maxillary contribution to an antorbital fossa. The premaxillary process has a triangular and distally tapering outline in lateral view. The dorsal margin of the premaxillary process is not straight but slightly angled midway where a slit-like articular facet for the maxillary process of the premaxilla starts. Therefore, the maxillary process of the premaxilla bordered the external naris rostroventrally. The jugal process is lower than the premaxillary process; it tapers distally, but tapering is minimal in the proximal segment and increases in correspondence of a change in inclination of the dorsal margin (the ‘step’ in Fig. 5). The segment caudal to this change in inclination is the portion that articulated with the jugal.

The left maxilla preserves 11 teeth in situ. The first tooth is missing, probably because of the damage to the tip of the premaxillary process; tooth 8 slipped out of its alveolus and covers the tip of the premaxillary process of the right maxilla; tooth 13 is represented by an empty alveolus. Therefore, this maxilla has 14 tooth positions. The right maxilla has 14 teeth in situ. Comparison with the left maxilla suggests that the first tooth of the series is tooth 1.

Nasal. An elongate (22 mm long), flat and thin bone is preserved between the maxillae and the mandibular rami (Fig. 3). Because of its position and morphology, it is tentatively identified as a nasal. Its rostral extremity tapers to a premaxillary process bounding dorsally a rostral notch corresponding to the dorsocaudal margin of the external naris. The maxillary process is overlapped and concealed by the right mandibular ramus and its dentition. The body of the nasal is straight and its dorsal margin is rectilinear. Its caudal end appears to be squared, but the caudoventral corner is concealed by other bones. Its ventral or ventrolateral margin is irregular and probably not the actual margin of the element but an artefact of preparation on a rather thin bone. As for its shape, size and position, the element could only be alternatively identified as a palatine. However, if it were the palatine, the notch corresponding to the choana should be situated caudally (see Ősi et al., 2010, figs. 1-2). This would imply an unlikely 180° rotation of the bone. The identification as a detached and drifted palatal plate of a maxilla (Ősi et al., 2010, fig. 8) seems also to be unlikely.

Frontal. A large fragment of a broad bone preserved dorsal to the occiput is tentatively identified as part of a frontal or of the fused frontals (Fig. 3). It does not show any crests or ridges and gives no information about the morphology of the frontals.

Postorbital. The postorbital is a triradiate (Y-shaped; Fig. 6A) and a very slender element. It closely resembles the postorbitals of Carniadactylus rosenfeldi (MPUM 6009) and Austriadraco dallavecchiai (see Dalla Vecchia, 2018, fig. 3A-B), but it is even more gracile. Its length from the distal extremity of the jugal ramus to the extremity of the exposed portion of the frontal ramus is 10.5 mm. Only the proximal part of the squamosal ramus is visible because the rest is covered by the left humerus. The slender frontal ramus is slightly curved with a rostroventral concavity; its distal end is covered by a cervical vertebra and the right tibia. The exposed portions of the squamosal and frontal rami form an angle of about 85°. This indicates that the upper temporal fenestra had a relatively acute ventrolateral margin (this angle is about 70° in Carniadactylus rosenfeldi and about 80° in Austriadraco dallavecchiai, but these values are based on more complete squamosal rami; Dalla Vecchia, 2018). The long and very slender jugal ramus is curved with rostral concavity and tapers distally where there is a caudoventral facet for the articulation with the postorbital process of the jugal. Frontal and jugal rami border the caudal part of the broad orbit; their curvature and length, united to those of the postorbital process of the jugal, suggest the presence of a circular and very large orbit.

Jugal. The right jugal is exposed in lateral view (Figs. 6B and 6C) and is tetraradiate as in many other basal pterosaurs (Wellnhofer, 1978, 2003; Dalla Vecchia, 2014). It is not fused with the maxilla, postorbital and quadratojugal. Its length is 17 mm from the caudal extremity of the quadratojugal process to the rostral end of the maxillary process. The postorbital process is much longer than the other processes; it is slender and tapers distally. Although the distal termination of this process is broken and is not preserved, its maximum length can be estimated based on the convergence of its cranial and caudal margins and comparison with the jugal process of the postorbital (see Fig. 7A). The postorbital process is nearly straight and caudally inclined at about 130° with respect to the axis of the jugal body. Its orbital margin is thickened. The maxillary process is ventrally deflected at about 20° with respect to the axis of the jugal body. It is deep proximally where it contributes to the caudal end of the ventral margin of the antorbital fenestra and tapers to a needle-like point distally. A very small notch is present along the ventral margin. The lacrimal process is rostrodorsally directed and forms an angle of about 35° with the axis of the jugal body. This process is very short, appearing as a triangular spur. It is partially overlapped dorsally by a rod-like bone. Comparison with E. ranzii (see Wild, 1979, fig. 1), Carniadactylus rosenfeldi (see Dalla Vecchia, 2018, fig. 2) and Raeticodactylus filisurensis (see Stecher, 2008, fig. 6) suggests that this latter element is part of the damaged lacrimal. This suggests also that the short lacrimal process might be incomplete and was longer originally, but its relatively narrow base and tapering margins indicate that it could not be much longer than preserved. A short, triangular process of the jugal is damaged distally and forms the ventral margin of the lower temporal fenestra. This process is clearly separated from a ventral strip of bone by a gap, but the gap becomes a ridge parallel to the ventral margin of the jugal rostrally (Figs. 6B and 6C). Comparison with the 3D-ct scans of the jugal of Caelestiventus hanseni (see Britt et al., 2018, fig. 3) suggests that this strip of bone in MFSN 21545 belongs to the thin ventral part of the jugal and is not the quadratojugal. The strip is broken and partly detached in MFSN 21545 because of the crushing of the jugal on other bones. Consequently, the quadratojugal process of the jugal is made of the triangular process forming the ventral margin of the lower temporal fenestra plus the caudal portion of the detached strip of bone and is damaged distally.

The jugal body is rectangular in lateromedial view and is slightly constricted dorsoventrally in the middle. The orbital margin is thickened. A large elliptical foramen pierces the bone at the point of minimum depth.

Cranial fenestrae. The shape of the cranial openings can be reconstructed by returning the preserved skull elements to their original position. The articulation between the jugal and maxilla appears to differ among non-monofenestratan pterosaurs. In Dimorphodon macronyx (see Sangster, 2003, fig. 2.9) and Caelestiventus hanseni (F.M. Dalla Vecchia, 2018, personal observation) the jugal overlaps the jugal process of the maxilla laterally, whereas it overlaps the jugal process of the maxilla dorsally in E. ranzii (see Wild, 1979, fig. 1) and Carniadactylus rosenfeldi (see Dalla Vecchia, 2018, fig. 2). When the jugal and maxilla of MFSN 21545 are returned to their articular position with the jugal that overlaps the jugal process of the maxilla dorsally (Fig. S3A), the last two maxillary teeth lie below the jugal and the resulting antorbital fenestra is very long and has a ‘step’ in its ventral margin that is not observed in any other pterosaur. When the jugal and maxilla are returned to their articular positions with the jugal being overlapped medially by the jugal process of the maxilla, the overlap ends rostrally where the change in inclination of the dorsal margin of the jugal process of the maxilla occurs (the ‘step’ in Fig. 5), as suggested by analogy with the maxillojugal of Caelestiventus hanseni (F.M. Dalla Vecchia, 2018, personal observation). However, two options exist. In the first, the last three maxillary teeth lie below the maxillary process of the jugal and are not covered labially by it, but the ventral margin of the antorbital fenestra possesses an unusual ‘step’ similar to that obtained by the dorsoventral overlap (Fig. S3B). In the second option, the jugal and maxilla overlap to form a ‘smooth’ (i.e. ‘step’-free) ventral margin of the antorbital fenestra (as is the case in other pterosaurs; see Raeticodactylus filisurensis in Fig. S4), the maxillary process of the jugal entirely covers the last tooth and partly also the penultimate tooth (Fig. 7A). This articulation between jugal and maxilla resembles that of Dimorphodon macronyx but the point of the maxillary process occurs ventrally in Seazzadactylus venieri instead of dorsally (cf. Sangster, 2003, fig. 2.9). The labial overlapping of the last two maxillary teeth could be a consequence of the crushing and flattening of the rostroventral margin of the jugal. This second option is chosen here in the assembly of the jugal, maxilla, postorbital and presumed nasal (Fig. 7A), and in the skull reconstruction (Fig. 7B). With this articulation, the axis of the jugal is oriented dorsocranially-ventrocaudally and the ventral margin of the skull at the articulation with the mandible is curved down caudally.

In the assembly, the jugal, maxilla, and postorbital articulate smoothly (Fig. 7A), but the placement of the presumed nasal is somewhat problematic. The bone appears to be of excessive size for a nasal, but it is now flattened, whereas it was dorsolaterally arched in vivo and thus would have been less exposed laterally than appears in Fig. 7A. Caudally, the nasal probably overlapped the frontal and extended over the orbit as in other pterosaurs. However, its exact position cannot be established because the rostroventral (maxillary) process is concealed by the right mandibular ramus. How it articulated with the maxilla is therefore unknown. The ascending process of the maxilla possesses a caudal articular facet along its apical part. This facet likely received the lacrimal as in the reconstructions of the skulls of E. ranzii, Carniadactylus rosenfeldi, Raeticodactylus filisurensis, Campylognathoides liasicus, Dorygnathus banthensis and Scaphognathus crassirostris (Wellnhofer, 1978; Sangster, 2003). The rostroventral process of the nasal articulates dorsally with the ascending process of the maxilla in the reconstructions of these taxa and in those of Rhamphorhynchus muensteri and Angustinaripterus longicephalus (see Sangster, 2003). In the tentative reconstruction of the skull (Fig. 7B), the presumed nasal of MFSN 21545 is placed in a rostral position based on this dorsal articulation of the nasal with the maxilla. The original slope of the nasal is unknown, as also are the length and orientation of the caudal processes of the premaxilla. Consequently, the reconstructed shape and size of the external naris are tentative. Although most of the lacrimal is not preserved, the inclination of the lacrimal process of the jugal and the ascending process of the maxilla show that the antorbital fenestra was large and shaped like an isosceles triangle (Figs. 7A and 7B), more similar to the large and oval antorbital fenestra of Raeticodactylus filisurensis (see Stecher, 2008; Fig. S4), than the smaller and D-like antorbital fenestra of E. ranzii (see Wild, 1979). The orbit is very large and sub-circular; as in many other basal pterosaurs, it is the largest skull opening. The shape of the lower temporal fenestra cannot be known exactly because the quadratojugal is not preserved, but the lengths of the postorbital process of the jugal and of the jugal process of the postorbital indicate that it was very long caudodorsally to rostroventrally and probably rather narrow. The lateroventral margin of the upper temporal fenestra is V-shaped as in Carniadactylus rosenfeldi, Austriadraco dallavecchiai and Campylognathoides liasicus. As in the reconstructions of the skull of Carniadactylus rosenfeldi by Wild (1979, fig. 2), the upper temporal fenestra had probably the outline of an inverted tear-drop.

Squamosal. Part of the left squamosal appears still to be connected to the left side of the occiput, but is intensely deformed and broken because of strong crushing. A large fragment lateral to the left paroccipital process bears a shallow and rimmed, elliptical socket that is 1.25 mm long, which corresponds in size with the proximal articular head of the quadrate. This socket could be the cotyle for the quadrate. A rounded bone with a pointed process, located close to the left wing phalanges 2 and 3 (Fig. 3), could be a disarticulated, displaced and strongly crushed right squamosal. Identification is based on the size and shape of the element, in particular the shape of its process, which resembles the squamosal descending flange that overlaps the caudal or caudolateral surface of the quadrate in Carniadactylus rosenfeldi (see Wild, 1979, fig. 2), Dorygnathus banthensis (see Padian, 2008a, figs. 6 and 16), Campylognathoides liasicus (see Wellnhofer, 1974, fig. 2; Padian, 2008b, figs. 4 and 6), Scaphognathus crassirostris (see Wellnhofer, 1975b, figs. 33 and 34a) and in many other pterosaurs (e.g. Wellnhofer, 1978, figs. 2, 4 and 5; Codorniú, Paulina-Carabajal & Gianechini, 2016, figs. 1D and 8).

Pterygoid and ectopterygoid. A skeletal element with four slender and pointed processes (Figs. 8A and 8B) is preserved isolated just dorsal to the right maxilla and the right jugal. Assuming that the element retains its anatomical orientation, its caudal portion bears two paired, recurved, and caudally directed processes at its caudal end and a third, straight and caudolaterally or caudomedially directed process in a more rostral position. The outer margin of this third process is thickened and ridge-like; this ridge extends along the margin of the rectangular main body of the skeletal element. The fourth and rostral process is actually a 90° bend in the bone and tapers distally. A ridge originating at the proximal part of the rostral process extends longitudinally along the main body of the bone. A partially exposed skeletal element with the same recurved caudal processes occurs between the right jugal and the right mandibular ramus (Fig. 8C). However, the two recurved processes are differently oriented with respect to their homologues on the other skeletal element, suggesting that they may belong to a skeletal element that is tightly connected but distinct from the main body and not fused to it. The possible boundary between these two elements is indicated in Fig. 8B.

Their position with respect to the maxillae, right jugal and mandibular rami, and their morphology, suggest that these bones are palatal elements. Because of their position and size, they are plausibly the pterygoids with the ectopterygoids preserved in dorsal or palatal view (e.g., Ősi et al., 2010, fig.1 and 8B). They are probably flattened by crushing and the various processes may lie artificially in the same plane. Their right-left polarity cannot be unambiguously established based on their position alone, but the completely exposed bone is probably the right one in palatal view (see below).

The morphology of these elements is unlike that of the pterygoid-ectopterygoids of other basal pterosaurs, namely Carniadactylus rosenfeldi (see Dalla Vecchia, 2009a, fig. 2A); Dorygnathus banthensis (see Ősi et al., 2010, figs. 2, 6B, and 8B), Campylognathoides liasicus (see Wellnhofer, 1974, figs. 2 and 4; Padian, 2008b, pl. 7/figs 2 and 5, fig. 8), Cacibupteryx caribensis (see Gasparini, Fernandez & De La Fuente, 2004, fig. 2D), Scaphognathus crassirostris (see Wellnhofer, 1975b, figs. 33a and 34b; Bennett, 2014, fig. 5B) and Rhamphorhynchus muensteri (see Wellnhofer, 1975a, fig. 3d; Ősi et al., 2010, figs. 1C-D and 9A). The partially exposed pterygoid of Dimorphodon macronyx also appears to be different from that of MFSN 21545 (Sangster, 2003, fig. 2.9). Particularly, the ectopterygoids of those pterosaurs occur in a rostral position with respect to the pterygoid. None of these other taxa has a rostral process that is bent at 90°. The paired recurved processes of the ectopterygoid resemble those of the ectopterygoid of the theropod dinosaur Allosaurus fragilis (see Madsen, 1976, pls. 2B and 10D) in respect of their overall morphology and their position relative to that of the pterygoid, although the ectopterygoid of this dinosaur is proportionally larger than that of MFSN 21545. The pterygoid of Allosaurus fragilis is straight in palatal view (Madsen, 1976, pls. 2B) unlike that of MFSN 21545. The pterygoid-ectopterygoid of the basal pterosaur Sordes pilosus (the paratype PIN 2470 1B, F.M. Dalla Vecchia, 2018, personal observation on photographs) differs from those of other pterosaurs reported in literature and may be like that of MFSN 21545, including in regard to the 90° bending of the rostral process of the pterygoid. Unfortunately, the palate of Sordes pilosus was never described and figured in detail.

The tentative identification of the processes of the pterygoid-ectopterygoid of MFSN 21545 in Fig. 8 is essentially based on the pterygoid-ectopterygoid of Allosaurus fragilis. The longer and more slender of the two recurved processes of the ectopterygoid has a long facet that could represent its sutural facet with the jugal (Figs. 8A and 8B), and can therefore be interpreted as the jugal process, which was originally directed laterally and forming the rostral margin of the subtemporal fenestra and the caudal margin of the suborbital fenestra. Consequently, the other recurved process is the caudal process of the ectopterygoid, which overlapped the pterygoid laterally in Allosaurus fragilis (Madsen, 1976, pl. 2); if so, the ectopterygoid would be somewhat displaced from its anatomical articulation with the pterygoid. The rostral process of the pterygoid would be a laterally bent palatine ramus, whereas the straight caudal process would be the quadrate ramus.

Two thin and paired bones occurring between the two pterygoids and partly overlapped by the jugal process of the right maxilla (Fig. 3) may be tentatively identified as the epipterygoids.

Quadrate. The left quadrate is exposed in caudomedial view. It is slightly shifted craniomedially from its anatomical position and overlaps the basisphenoid (Figs. 9A and 9B). The right quadrate is partly preserved and is rotated 90° counter-clockwise in the plane of the occiput from its anatomical position. In caudomedial view, the quadrate is dorsoventrally elongate and strap-like as in other non-pterodactyloid pterosaurs. The proximal portion tapers to a small and rounded articular condyle. The shaft has a straight and thickened lateral margin. The thin and broad medial lamella is partly preserved in the left quadrate. The distal portion with the mandibular condyle and the pterygoid ramus is covered or poorly preserved in both elements.

Braincase. The trapezoidal occiput is exposed in caudal view (Figs. 9A and 9B). Unlike the remaining part of the skull, it is not disarticulated, suggesting that the bones forming it were firmly connected. The exposure and overall morphology of this part of the skull resemble those of the holotype of Carniadactylus rosenfeldi (see Dalla Vecchia, 2009a, fig. 2A). The occipital condyle is 2.35 mm wide and 1.8 mm high, kidney-shaped and convex. It is comparatively larger with respect to the condyles in pterodactyloids, which have occipital condyles with a rounded outline (e.g., Wellnhofer, 1985, fig. 34; Bennett, 2001, figs. 8-9). There are no visible sutures between the condyle and the basioccipital and between the condyle and the exoccipitals, with the result that the contributions of these bones to the condyle are unclear. The foramen magnum can be identified above the occipital condyle, but its size and outline are affected by crushing. The foramen magnum is bordered dorsally and laterally by the supraoccipital, which is strongly crushed, and its margins cannot be identified with confidence. Portions of the left squamosal and parietals are probably present (Figs. 9A and 9B), but they are strongly crushed and their outlines are unclear. The paroccipital processes project lateral to the occipital condyle, expanding at their lateral extremities. The dorsoventrally narrow portions of the processes that border the foramen magnum ventrally are probably formed by the exoccipitals as in other pterosaurs (e.g. Rhamphorhynchus muensteri, Wellnhofer, 1975a, fig. 4a; Padian, 1984, fig. 2), but sutures between the exoccipitals and opisthotics cannot be identified.

The posttemporal fenestrae, which are present in all pterosaurs (e.g., Wellnhofer, 1975a, fig. 4a; Wellnhofer, 1985, fig. 34; Kellner & Tomida, 2000, fig. 9; Bennett, 2001, fig. 9; Codorniú et al., 2016, fig. 1c) cannot be identified dorsal to the paroccipital processes of MFSN 21545, but they might have been closed by the strong compression and crushing that affected the skull. The foramina for the caudal middle cerebral vein, which are reported in Allkaruen koi (see Codorniú et al., 2016, fig. 1c) and Rhamphorhynchus muensteri (see Wellnhofer, 1975a, fig. 4a) cannot be identified in Seazzadactylus venieri.

The basioccipital is hourglass-shaped, very narrow transversely, and much expanded at its ventral boundary with the basisphenoid. The basioccipital and basisphenoid are fused to one another without an apparent suture. The left basal tuber is more developed than the right one, but it is less robust than the basal tubera of Allkaruen koi (see Codorniú et al., 2016, fig. 1c). Like the holotype of Carniadactylus rosenfeldi, MFSN 21545 has large D-shaped to drop-shaped depressions that are each bordered by the basioccipital medially, the basisphenoid ventrally and the paroccipital processes dorsally (Figs. 9A and 9B). Each depression is bordered laterally by a thin crista tuberalis, which is possibly the ventral ramus of the opisthotic fused to the basal tubera (Gower & Weber, 1998). Plausibly, those depressions were originally deeper rostrocaudally in both specimens before the strong crushing of the skulls and contained one or more foramina that were closed and concealed by crushing. Dalla Vecchia (2009a, fig. 2) reported this depression as the ‘fossa with the vagus foramen’ in Carniadactylus rosenfeldi, while it is referred to as paracondylar recess by Codorniú et al. (2016) in the uncrushed skull of Allkaruen koi, a term that is adopted here. The paracondylar recess of Allkaruen koi is comparatively smaller than those of the two Italian taxa and is mostly occupied by a very large foramen (referred to as the metotic foramen for the exit of nerves IX-XI by Codorniú et al., 2016). A much smaller foramen occurs at the medial margin of the recess in Allkaruen koi and is considered to be the foramen for nerve XII (Codorniú et al., 2016, fig. 1c). Rhamphorhynchus muensteri has an undivided and very large foramen in the paracondylar recess (Wellnhofer, 1975a, fig. 4a; Padian, 1984, fig. 2B) that can be considered a metotic foramen (Gower & Weber, 1998). The paracondylar recess of Dorygnathus banthensis (SMNS 50164; Fig. 9D) is different: it is crossed by a septum that divides it into two large and deep depressions. The dorsolateral depression (as preserved, but in the uncrushed skull was probably somewhat caudolateral) is twice the size of the ventromedial one. Both depressions plausibly contained foramina and represent a divided metotic foramen. Therefore, the larger dorsolateral depression may contain the jugular or vagus foramen transmitting the cranial nerves X, XI (if present), and possibly IX and the jugular vein, whereas the ventromedial depression may contain the fenestra pseudorotunda (for the attachment of a secondary tympanic membrane) and possibly the foramen for the nerve IX (Gower & Weber, 1998).

The paracondylar recess of Carniadactylus rosenfeldi is undivided (Dalla Vecchia, 2009a, fig. 2). The condition of the paracondylar recess of Seazzadactylus venieri is not immediately clear because the left recess appears to differ from the right one (Figs. 9A and 9B). No bone septum divides the left recess, while a thick bar of bone crosses the right recess close to its medial margin. This bar does not appear to be fused with the margins of the recess, and is thus plausibly part of an underlying bone (the prootic?) emerging through the recess because of crushing. Therefore, the paracondylar recesses of both Seazzadactylus venieri and Carniadactylus rosenfeldi probably contained an undivided metotic foramen.

The basisphenoid (probably a parabasisphenoid as in most reptiles) and its basipterygoid processes are flattened in the same vertical plane as the occipital condyle and the foramen magnum, but were originally directed ventrorostrally (Codorniú et al., 2016, fig. 1a). As in Dorygnathus banthensis (see Padian, 2008a, figs. 12 and 17), Bellobrunnus rothgaengeri (see Hone et al., 2012, fig. 4) and probably Carniadactylus rosenfeldi (Dalla Vecchia, 2009a, fig. 2A) as well, the basisphenoid is subrectangular, nearly as broad as long, and with basipterygoid processes projecting at its lateroventral corners. The proximal part of the basisphenoid near the distal rim of the basioccipital is concave as in Carniadactylus rosenfeldi (see Dalla Vecchia, 2009a, fig. 2A). This concavity corresponds to the basioccipital–basisphenoid fossa of Gower & Sennikov (1996). The basipterygoid processes of the basisphenoid are long, rod-like, and slightly splayed laterally as in other non-monofenestratan pterosaurs (e.g. Carniadactylus rosenfeldi, Dalla Vecchia, 2009a, fig. 2A; 2014, fig. 4.1.103; Raeticodactylus filisurensis, Dalla Vecchia, 2014, fig. 4.1.160; Dorygnathus banthensis, Padian, 2008a, pl. 5/fig. 3, pl. 8/fig. 2, figs. 12 and fig. 17; and Fig. 9D; Rhamphorhynchus muensteri, Wellnhofer, 1975a, fig. 3d). Although unreported by Wellnhofer (2003) and Kellner (2015), the holotype of Austriadraco dallavecchiai also has a partially preserved occiput (Fig. 9C) and basipterygoid processes of the basisphenoid that are rod-like, elongated and slightly splayed laterally. This specimen does not show any trace of the cultriform process of the parasphenoid (reported also as “parasphenoidal rostrum”; Romer, 1956, p. 87) like that observed in Dorygnathus banthensis (see Padian, 2008a, fig. 12, but apparently absent in Fig. 9D), Rhamphorhynchus muensteri (see Wellnhofer, 1975a, fig. 3d), Scaphognathus crassirostris (see Wellnhofer, 1975b, fig. 35), Cacibupteryx caribensis (see Gasparini, Fernandez & De La Fuente, 2004, fig. 2D) and Bellobrunnus rothgaengeri (see Hone et al., 2012, fig. 4). This feature cannot be checked in Seazzadactylus venieri because the basisphenoid is covered distally by the left quadrate; this is also the case in Carniadactylus rosenfeldi where most of the basisphenoid is overlapped by a cervical vertebra and the parasphenoid rostrum—if present—is concealed by the right mandibular ramus (Dalla Vecchia, 2009a, fig. 2A). Maybe the cultriform process was not fused to the braincase in the holotype of Austriadraco dallavecchiai and displaced. Alternatively, it might have been broken or unossified.

Some elements occurring in the skull region close to the left wing phalanx 2 (Fig. 3) remain indeterminate, but they may belong to the braincase due to their size, morphology and position.

Mandible

The two mandibular rami are associated with the skull and lie parallel to one other (Figs. 10A and 10B). The left ramus was shifted caudally with respect to the right ramus. The right ramus shows the lateral side and partly covers the left ramus in the middle. The left ramus is partly damaged by a fracture. The mandibular ramus is slender with a length/height ratio at mid ramus of 17.8 (length is 53.5 mm and height is only three mm).

Its rostral end is straight and sharply pointed, and the dentaries are not fused at the symphysis, which was probably very short. The dorsal margin of the ramus is shallowly concave in lateral view, while the ventral margin is straight. Height is constant along most of dentary, but the ramus slightly flares by mandibular tooth 4 and tapers rostrally to tooth 2. An arched longitudinal ridge, which is bordered by narrow ventral and dorsal grooves, runs along the lateral side of the dentary from tooth 4 to the last tooth. There is no external mandibular fenestra. Just caudal to the position of the external mandibular fenestra in Austriadraco dallavecchiai (Figs. 10C–10F), some teeth of the underlying left mandibular ramus pierced the wall of the right ramus and are exposed. This suggests that the wall was very thin in that area and could be easily broken, as in the case of Dimorphodon macronyx (see Bennett, 2015) and Caelestiventus hanseni (see Britt et al., 2018).

The dorsal margin of the ramus between the last tooth and the glenoid for the quadrate (Figs. 10C and 10D) shows the ‘two-peaked’ shape reported by Dalla Vecchia (2009a, p. 182; see also 2014, p. 82) as a peculiarity of Austriadraco dallavecchiai (Figs. 10E and 10F). The dorsal margin of the ramus has a small convexity just caudal to the last tooth which is followed by a straight segment (shallowly concave in the case of Austriadraco dallavecchiai) and then by a rounded process (the dorsal process of the surangular or ‘coronoid’ process). The latter is fractured at its base by crushing, which shows that it is a mediolaterally thin prominence. The retroarticular process is long and its caudal end is dorsoventrally expanded, lateromedially flattened and possesses a rounded profile in lateral view. It is slightly ventrally deflected, making with the dentary axis an angle of only 10–12°.

Hyoid apparatus

Rod-like bones that lie parallel to one other and to the mandibular rami are the ossified ceratobranchials I of the hyoid apparatus. One lies ventral to the mandibular rami in its natural position, whereas the other is slightly displaced dorsocaudally and lies near the caudal part of the left mandibular ramus (Fig. 3). They are nearly straight and slightly expanded at their extremities like those of Carniadactylus rosenfeldi (see Dalla Vecchia, 2009a, fig. 2).

Dentition

The dentition of this specimen is the most completely preserved among known Triassic pterosaurs with multicusped teeth except for that of the holotype of E. ranzii (see Dalla Vecchia, 2014). It is composed of four premaxillary, 14 maxillary and 21 mandibular teeth per side.

Premaxillary teeth. Four premaxillary teeth are outside their alveoli but close to the rostral tip of the premaxillae. Two right alveoli can be identified, but only one—the last and presumably that of tooth 4—is clearly visible (Fig. 4), whereas the first two alveoli are covered by a shed tooth. The shed teeth may be the right teeth 1–4. The first left tooth, still in situ at the apex of the rostrum, points forwards and its crown is slightly recurved rostroventrally. It is followed distally by another left tooth still in its alveolus, but pushed inside the premaxilla by crushing and appearing as a small mound on the dorsal surface of the bone (Fig. 4); since it occurs at the same distance from the tip of the snout as the last right alveolus, it is probably the left tooth 4.

The crowns of the shed teeth are similar in shape and size to those of the symphysial mandibular teeth, but they are slightly more slender. They are unicuspid, conical and recurved. The crown of left tooth 1 is slightly flattened labiolingually and is recurved with the concave side facing ventrodistally. The other teeth are shed; thus, their orientation must be deduced by comparison. Thin, straight and spaced apicobasal enamel ridges are present only on one side, whereas the rest of the surface is smooth (compare Figs. 11A, 11B and 11C, 11D). Crown curvature is seen in teeth showing the smooth side. The labial side of the first two unicuspid mandibular teeth is smooth, whereas the lingual side has apicobasal enamel ridges. In the unicuspid mandibular teeth 1–3 of Raeticodactylus filisurensis, the enamel wrinkles occur only on the lingual side (Stecher, 2008). This suggests that the side with basoapical enamel ridges of the premaxillary teeth of Seazzadactylus venieri is the lingual one; consequently, crowns of Figs. 11A and 11B are lingually and linguodistally recurved, respectively, while those of Figs. 11C and 11D are distally recurved (if they are all from the right premaxilla). The total basoapical length of the teeth is 4.2–4.5 mm. The ‘root’ is only slightly longer than the crown and there is no constriction between crown and ‘root’. One tooth (Fig. 11D) has an exposed pulp cavity because the side of the tooth was damaged or it was reabsorbed by a growing replacement tooth.

Maxillary teeth. Maxillary crowns are exposed in labial view in both maxillae. All crowns have smooth surfaces. Teeth 8, 10, 14 and possibly tooth 1 on the right maxilla and teeth 6 and 14 on the left maxilla are not fully erupted. The positions of the left teeth 8 and 13 are represented by empty alveoli, but the displaced tooth 8 is preserved close by its alveolus. Crowns 3, 5 and 7 are 1.75 mm high and crown 9 is 1.60 mm high; the penultimate right crown is one mm high like the left crown 12. Maxillary tooth crowns are slightly larger than mandibular crowns (like Raeticodactylus filisurensis; Dalla Vecchia, 2014, fig. 4.1.161C); this size difference is more marked in the mesial half of the maxillary dentition (see Fig. S5). In the right maxilla, crowns 1–7 are basoapically higher than mesiodistally long, crown 9 is as high as long and the last three crowns are much longer than high. In the left maxilla, crown 2 is basoapically higher than mesiodistally long, crowns 5 and 8 are slightly apicobasally higher than mesiodistally long, whereas crowns 9–12 are longer than high. The first three crowns are slightly procumbent and slightly recurved backwards with curvature decreasing from tooth 1 to 3, whereas the following crowns are upright and straight. Crowns are not contacting one other, but the mesiodistal spacing between mid-maxilla fully erupted teeth is less than half the mesiodistal length of a fully erupted crown.

With the possible exception of the first tooth (Fig. 12A), crowns are multicusped (Figs. 12B–12I). The main cusp is triangular in labial view and moderately flattened labiolingually. The first three maxillary crowns differ slightly from the first two or three multicusped mandibular teeth, whereas crowns distal to maxillary tooth 3 have a similar shape as the mandibular crowns distal to tooth 4 or 5.

In the left maxilla tooth 1 is missing. The crown of the right tooth 1 (Fig. 12A) has an inflated basal part and a distally recurved apical part. It is smaller than the following teeth and possibly not fully erupted. A very small accessory cusp might be present distally, but the crown appears to be basically unicuspid and resembles the premaxillary crowns. The cuspidation pattern of the following teeth is summarised in Fig. 13. Crowns are mainly pentacuspid with two mesial and two distal accessory cusps (Figs. 12D, 12E and 12I), but there is also a pentacuspid crown with three distal and one mesial accessory cusps (Fig. 12C), a heptacuspid crown with three mesial and three distal accessory cusps (Fig. 12E), three hexacuspid crowns with two mesial and three distal accessory cusps (Fig. 12G) and two tetracuspid crowns with one mesial and two distal accessory cusps (Figs. 12B and 12H). There are no fully erupted tricuspid teeth. Accessory cusps increase in size from the basal to the apical one. The cuspidation pattern differs in corresponding teeth of the left and right maxillae (Fig. 13), as it was observed in E. ranzii (see Wild, 1979).

The basal part of the crown has a more or less developed pit in all teeth, which could be due to basal resorption by the growing replacement tooth, as in some mandibular crowns (see below), but it was most probably caused by the collapse of its pulp cavity.

The ‘root’ is visible only in the displaced left tooth 8: it is tongue-shaped and as deep as the crown is high.

Details of the individual teeth are reported in SI2.

Mandibular teeth. The right mandibular ramus exposes its entire dentition (21 teeth) in labial view (Fig. 14). Teeth 5, 18, 20 and 21 are not fully erupted. The ratio of tooth number/mandible length is 0.39. The dentition of the left mandibular ramus, exposed in lingual view, is mostly covered by the right ramus. The first left mandibular tooth is in situ whereas the second is out of its alveolus but close by. Crushing and probably preparation caused three mid-distal left mandibular crowns (approximately corresponding to teeth 13–15) to crop out through the right ramus and be partially visible (Figs. 10C and 10D).

The first two mandibular teeth (Figs. 15A and 15B) have unicuspid, conical and pointed crowns that are relatively stout and slightly recurved backwards. These crowns are slightly bulkier than the premaxillary crowns. They are procumbent; the first more than the second. These crowns are not much larger than those of fully grown mid-mesial multicusped mandibular teeth (they are ca. 2.6 and 2.2 mm basoapically high, respectively, whereas crown 12 is ∼1.5 mm high). The lingual side of the crown (visible in the left teeth) has thin, straight and spaced basoapical enamel ridges, whereas the labial side is smooth.

A 1.3 mm-long gap separates crown 2 from crown 3. All crowns from crown 3 to 21 are multicusped, with one main central cusp and 1–3 accessory cusps along each mesial and distal margin (Figs. 14 and 15C–15H). All multicusped crowns have smooth surfaces. Crowns are conical and slightly labiolingually compressed, with an upright main cusp and basally-positioned accessory cusps. Cuspidation pattern is summarised in Fig. 14. Crowns are mainly pentacuspid with two mesial and two distal accessory cusps (Figs. 15E–15G), but tooth 3 has a heptacuspid crown with three mesial and three distal accessory cusps (Fig. 15C), tooth 13 has a hexacuspid crown with two mesial and three distal accessory cusps (Fig. 15H), teeth 4 and 19 have tetracuspid crowns with two mesial and one distal accessory cusps (Fig. 15D) and tooth 14 may have a tetracuspid crown with one mesial and two distal accessory cusps. The overall shape of crowns 3–4 is unlike that of the following crowns. Crowns 3–4 have small accessory cusps, whereas these cusps are larger in tooth 6 and following teeth and the apical accessory cusps are larger than the basal accessory cusps (Figs. 15C–15H). The main cusps are more flattened labiolingually in crown 6 onwards than in crowns 3–4. Crowns 3–4 are apicobasally much higher than mesiodistally long (Figs. 15C and 15D); crowns 6–7 are also apicobasally higher than mesiodistally long, but are comparatively longer mesiodistally than the preceding crowns (Fig. 15E); crowns 12 and 14 are nearly as mesiodistally wide as apicobasally tall and are the largest multicusped crowns in the mandible (height ∼1.5 mm). In the most distal teeth, crowns become mesiodistally longer than apicobasally high and with a slightly asymmetrical main cusp.

Spacing of the multicusped crowns is in general ca. 0.25 mm, that is, much less than half the mesiodistal length of the crown of a fully grown tooth; the splayed accessory cusps of adjacent teeth sometimes contact or even overlap.

Right teeth 11 and 16 (Fig. 15G) show the apical part of the replacement tooth growing inside the pulp cavity of the functional tooth because the functional crown is labially reabsorbed. Right crowns 10, 12–15 and 17 have a basal depression, possibly due to reabsorption by the replacement crown growing inside the basal part of the functional crown or because of the collapse of the pulp cavity.

Axial skeleton

The vertebral column is disarticulated and its elements scattered. The caudal segment is totally missing.

Cervical vertebrae. Six cervical vertebrae can be identified based on their position, size and peculiar morphology (Dalla Vecchia & Cau, 2015). Part of the atlas is preserved on the left quadrate near the occipital region of the skull (Figs. 9A and 9B). It is craniocaudally short, kidney-shaped and with remnants of the pedicels, potentially representing the intercentrum of the atlas in craniocaudal view with part of the atlas neural arch (cf. Bennett, 2001). A cervical vertebra in left lateral view close to this bone (Fig. 3) is identified as the third cervical based on its position, size, outline of the neural spine and the well-developed prezygapophyses. The axis is mostly covered by the atlas intercentrum and by the cervical vertebra 3. The other three cervicals occur near the scapulocoracoids (Fig. 2); the most proximal of the three is exposed in left lateral view, while the other two are probably in ventral view and badly crushed.

Dorsal vertebrae. Only seven out of the 14–16 dorsal vertebrae present in non-monofenestratan pterosaurs (Wellnhofer, 1975a; Wild, 1979; Padian, 2008a, 2008b; Bennett, 2014) can be reliably identified in the slab. They are gathered in two groups: one, proximal, is located between the scapulocoracoids (Fig. 2), whereas the other, distal, is close to the sacral vertebrae and the pelvis (Fig. 16). The many missing vertebrae are probably covered by other bones or were preserved in the portions of the slab that got lost. The better preserved dorsal vertebra of the first group is exposed in dorsal view and has a long and thin transverse process. It is as large as the cervicals and thus it is one of the anteriormost dorsals. Another vertebra that is close to the shaft of the right coracoid is much smaller. It is exposed in ventral view and also has a long transverse process directed caudolaterally; its centrum is cylindrical and unconstricted. The four dorsals of the second group are disarticulated, but close to one other. The last dorsal is exposed in right lateral view, the penultimate in caudal view and the other two in cranioventral view (Fig. 16). In lateral view, the centrum has a concave ventral margin. The cranial articular surfaces of the centra of the first two vertebrae of the second group are kidney-shaped (lower than wide) and concave; the caudal articular surface of the centrum of the penultimate dorsal also appears to be kidney-shaped and slightly concave. The postzygapophyses are smaller than the prezygapophyses. Although the last dorsal lacks transverse processes, these processes appear to be present in the penultimate dorsal. The last dorsal has a square neural spine that is slightly longer than high. The first two dorsals of the second group have associated ribs.

Cervical and dorsal ribs. Only shaft fragments and portions of the tubercula and capitula of the cervical and dorsal ribs are preserved. The ribs of the third to last dorsal vertebra are apparently dicephalous and have an unusually short shaft with a blunt distal end (Fig. 16B).

Sacral vertebrae. Three co-ossified sacral vertebrae are exposed in left lateral view near the last dorsal vertebra (Fig. 16). The faint suture between the centra of the sacrals 1 and 2 can be seen only under ethanol immersion. The neural spines are rectangular and that of the first sacral is taller than long. A fan-shaped sacral rib crops out from below the sacral vertebra 2. The sacrum is not co-ossified with the sacral ribs and the sacral ribs are not fused with the ilia.

Sternum. Only the ?left half of the sternum is preserved (Fig. 17). It is a thin and broad plate with a triangular cranial portion and a square posterior part bearing three short lateral processes for the sternal ribs. Only the base of the cristospine is preserved and the caudal portion of the plate is concealed by the right humerus. This sternum resembles those of E. ranzii (see Wild, 1979, fig. 14) and MPUM 7039 (Dalla Vecchia, 2014, fig. 4.2.2A).

Gastralia. The gastralia are very thin bones that are straight or curved at one extremity and pointed at the other (Fig. 17). They are scattered around the sternum and the girdles.

Pectoral girdle

The scapula and coracoid are fused. The right and left scapulocoracoids are exposed in lateral and medial view, respectively (Fig. 18). They are close and parallel to one other as is sometimes found to be the case in disarticulated pterosaur skeletons (e.g., Wild, 1979, pl. 8; Padian, 2008a, pl. 4/fig. 7).

The right coracoid lacks the distal portion of its shaft, and both scapulae also lack their distal portions. The shaft of the left coracoid is mostly missing; it is unclear whether this is due to the loss of fragments of the damaged slab and or to preparation and the imprecise fit of the slab fragments. The coracoid has a prominent biceps tubercle (sensu Bennett, 2003) at its dorsal extremity like the coracoids of Carniadactylus rosenfeldi and Austriadraco dallavecchiai and a coracoid tubercle (sensu Bennett, 2003) craniolaterally in the same position as in the coracoid of Carniadactylus rosenfeldi (Dalla Vecchia, 2009a; fig. 3). A small tubercle that is lower than the biceps tubercle occurs dorsal to the lower tuberosity (sensu Sangster, 2003) along the dorsal margin of the scapulocoracoid as in other Triassic pterosaurs (Dalla Vecchia, 2009a; fig. 3). This could be a remnant of the ‘acromion’ of the scapula after the fusion of scapula and coracoid. The glenoid is bordered by the lower tuberosity cranially and by the supraglenoidal buttress (sensu Sangster, 2003) caudally. The shaft of the right coracoid is flat and broad like those of Carniadactylus rosenfeldi and Austriadraco dallavecchiai, with parallel cranial and caudal margins (or craniomedial-caudolateral, according to its—unknown—articulation with the sternum). The angle between the right scapula and right coracoid is 76°. Distal to the glenoid the deep scapula exhibits a slight constriction (the scapular neck), beyond which the dorsal (dorsomedial, if crushing and flattening altered its original orientation) and ventral (ventrolateral) margins of the scapula diverge and the scapular blade flares markedly distally (Fig. 18).

Forelimb

The right forelimb preserved in articulation from the humerus to the wing phalanx 1 (Figs. 1 and 2). Only the proximal part of the wing phalanx 2 is preserved, along the margin of the slab. The left forelimb is moderately disarticulated and lacks only the greater part of the wing phalanx 4. Both forelimbs are flexed at the elbow with the humerus and paired radius and ulna aligned parallel to one other.

Humerus. The right humerus (Fig. 2) is exposed in dorsal view. Part of the external tuberosity and the saddle-like articular margin are preserved, but the deltopectoral crest is missing and was reconstructed. The distal part of the shaft is recurved cranially; the distal articular end is missing and was reconstructed. The left humerus is represented only by most of its crushed shaft (Fig. 2).

Radius and ulna. Radius and ulna are paired and lie parallel to one another in both forelimbs as is common in moderately disarticulated skeletons of early pterosaurs (e.g., Wellnhofer, 1975a, 1975b; Padian, 2008a, 2008b; Dalla Vecchia, 2014). The proximal portions of both radii and ulnae pairs are not preserved. The shafts of both elements are straight and have similar diameters. The right ulna (Figs. 19A and 19B) is exposed in dorsal view; its distal end bears a broad, flattened and wing-like crest like that on the upper surface of the distal part of the ulna in the holotype of Carniadactylus rosenfeldi (see Dalla Vecchia, 2014, fig. 4.1.113C1-2). The distal end of the right radius has a prominent longitudinal ridge bounded cranially by a broad furrow (Figs. 19A and 19B). The ridge could correspond to the distal tubercle of radii reported in other early pterosaurs (i.e. Carniadactylus rosenfeldi [see Dalla Vecchia, 2014, fig. 4.1.113C1-2] and Dimorphodon macronyx [see Sangster, 2003, fig. 3.7]); in which case the right radius is rotated so that its cranial side is partly exposed. The distal portions of the left radius and ulna differ noticeably in morphology from the distal ends of the right bones (Fig. S6). The distal termination of the left ulna, although partly reconstructed, is much more expanded than the distal termination of the radius. It closely resembles the distal end of the ulna of Rhamphorhynchus muensteri figured by Wellnhofer (1975a, fig. 12h) and comparison with it and with the associated radius indicates that the left ulna is exposed in cranial view (see also Bennett, 2001, fig. 76). It sends ventrally a flange like other pterosaurs (e.g. Rhamphorhynchus muensteri, Wellnhofer, 1975a, fig. 12h; Dorygnathus banthensis, Padian & Wild, 1992, pl. V, fig. 5). The moderately expanded distal end of the radius is divided into two condyle-like parts by a longitudinal furrow; comparison with the radius of Rhamphorhynchus muensteri figured by Wellnhofer (1975a, fig. 12g) and with the right radius suggests that the left radius is also in cranial view. The distal tubercle seems to be damaged.

Carpus. Both left and right carpi are exposed in dorsal view. The right carpus (Figs. 19A and 19B) is articulated with the radius-ulna and metacarpus. There is a single proximal syncarpal that is interlocked with a very large distal carpal. At least one, possibly two, other distinct and smaller elements crop out from below the cranial end of the proximal syncarpal, and do not contact the metacarpus. They are plausibly distal carpals that articulated with metacarpals I–III (Wellnhofer, 1975a, fig. 12a-b; Dalla Vecchia, 2009a, fig. 5A), which are slightly displaced and partially covered by the proximal syncarpal. They are damaged and their shape is therefore unclear.

A preaxial carpal with the same appearance as the right preaxial carpal of the holotype of Carniadactylus rosenfeldi and a similar position to it (see Dalla Vecchia, 2009a, fig. 5A) crops out cranially from the proximal part of metacarpal I.

The left carpus (Figs. 19C and 19D) is represented by a single carpal ‘block’ that is disarticulated and isolated but still very close to the radius-ulna and the wing metacarpal of the left wing (Figs. 1 and 2). The ‘block’ is made up of the interlocked proximal syncarpal and the large distal carpal. The cranial half of the left large distal carpal is apparently divided into at least two parts, but it is unclear whether this represents crushing of the irregularly shaped carpal or the existence of separate, distinct and smaller distal carpals. Comparison with the apparently homogeneous ‘nose’ of the right large distal carpal suggests that they are not distinct carpals. The carpal ‘block’ is rotated with respect to the left wing metacarpal and shows its dorsal side, as indicated by the position of the deep articular facet for the ulna in the proximal syncarpal.

The proximal syncarpals are saddle-like in dorsal view, thicker cranially (radial side), thinner caudally (ulnar side) and with a depressed ulnar facet. There is no suture between the radial and ulnar parts that compose each syncarpal. These elements resemble the proximal syncarpal of Carniadactylus rosenfeldi (see Dalla Vecchia, 2009a, fig. 5B), E. ranzii (see Wild, 1979, fig. 17) and Rhamphorhynchus muensteri (see Wellnhofer, 1975a, fig. 12b-f).

In dorsal view, the large distal carpals of MFSN 21545 are as craniocaudally broad as the proximal syncarpal and are proximodistally longer. The caudal half of each large distal carpal, which articulates with the wing metacarpal, is squared and massive, whereas the cranial half, which articulates with the metacarpals III, II and possibly I, is nose-like.

The actual shape of the preaxial carpal is unknown because it is partly concealed by the metacarpus (cf. Dalla Vecchia, 2009a, fig. 5).

Pteroid. A pteroid (Fig. 20) is preserved close by and parallel to the proximal part of the right wing phalanx 1. It is therefore shifted away from its natural articulation with the proximal syncarpal. Although it is closest to the right manus, the left manus is also close and disarticulated. Thus, it cannot be established whether it is a right or left pteroid. If it is the right pteroid, its proximal portion is exposed in ventro-caudal view, whereas the distal part is exposed in caudal view, due to mid-shaft fracturing and the slight rotation of the distal part. The distal portion is partly damaged, but its shape can be reconstructed without ambiguity. The pteroid has the shape of an exclamation mark, with a craniocaudally flattened shaft that broadens and becomes thinner distally. The distal end is spatula-shaped, thin and flattened. The shaft is straight, but it is slightly bent caudally at its beginning just distal to the proximal articular head. The latter is slightly expanded and subspherical. This 12.3 mm long pteroid is comparatively short compared with those of other Triassic pterosaurs (Table S1).

Metacarpus. The right metacarpus is perfectly articulated (Fig. 21). The metacarpals lie parallel to one another and metacarpals I–III overlap proximally and partly longitudinally. The distal ends of metacarpals II and III are covered by the ungual phalanx of left digit II. The left metacarpus is slightly disarticulated. The left wing metacarpal is close to the left wing phalanx 1, whereas the left metacarpals I–III have shifted ventrally as a unit. Left metacarpals I and II remained articulated to one other, while metacarpal III is disarticulated. Left metacarpals I and II expose their cranial side, showing the distal ginglymi, which have a broad intercondylar sulcus. The proximal extremities of left metacarpals I and II are convex. The shaft of left metacarpal I has a broad longitudinal groove, probably caused by the collapse of the thin cortex. The left metacarpal III has an asymmetrically expanded proximal end. Left metacarpals II and III have the same length (18 mm), whereas metacarpal I is decidedly shorter (it is 78% the length of metacarpal II).

The wing metacarpals (IV) are similar to the wing metacarpals of the other Triassic pterosaurs (Dalla Vecchia & Cau, 2015). They are much more robust than metacarpals I–III and slightly longer than metacarpals II–III. They have the same length as the wing metacarpal of the holotype of Carniadactylus rosenfeldi (21 mm). The left wing metacarpal is exposed in cranial view and shows a well-developed proximal ventral flange, a hint of the median tuberosity, the proximal depression for metacarpals I–III and the distal condylar end with a larger and slightly dorsally splayed dorsal condyle. The right wing metacarpal is exposed in caudodorsal view, showing a prominent crista metacarpi (Dalla Vecchia & Cau, 2015).

Phalanges of manual digits I–III. The left manus is disarticulated and the scattered phalanges of digits I–III are mixed together with those of the right manus, but left phalanges can be distinguished from right ones (Fig. 21). The phalangeal formula is 2-3-4-4-0. All non-ungual phalanges of digits I–III are straight. The penultimate (pre-ungual) phalanges are the longest (see Table S2); phalanx III-2 is the shortest phalanx in these digits (it is nearly half the length of phalanx III-3). In the penultimate phalanges, the shafts taper distally and the distal ginglymi are well-shaped, with a semicircular outline and lateral pits for the collateral ligaments. There is a small antungual sesamoid dorsally on all of these ginglymi. Similar sesamoids are reported in E. ranzii, Carniadactylus rosenfeldi, Peteinosaurus zambellii and MCSNB 8950 (Wild, 1979, 1994). The ungual phalanges are of similar sizes to one another (length range 6.2–7 mm, when not damaged). They are sharply pointed, moderately recurved and dorsoventrally flattened. They have a longitudinal groove for the attachment of the horny sheath and a large flexor tubercle. They resemble the pedal phalanges of the holotype of Carniadactylus rosenfeldi (see Dalla Vecchia, 2009a, fig. 8; 2014, fig. 4.1.128) and are only slightly larger than them (cf. Dalla Vecchia, 2009a, tab. 1). Unfortunately, no ungual phalanges of the pedes are preserved in MFSN 21545. Thus, it cannot be established whether Seazzadactylus venieri had manual unguals only slightly larger than pedal unguals (as comparison with the similarly-sized holotype of Carniadactylus rosenfeldi would suggest) or just smaller manual unguals with respect to Carniadactylus rosenfeldi. The rounded ginglymi of the penultimate phalanges allowed a high range of flexion and extension of the unguals.

Wing phalanges. Wing phalanx 3 is the longest and wing phalanx 1 the shortest (Table S1), but the length of wing phalanx 4 is unknown. As in other Triassic pterosaurs, the proximal part of wing phalanx 1 is enlarged and bear a robust extensor tendon process and a broad preaxial crest for additional insertion of the extensor tendon of the phalanx (cf. Wellnhofer, 1991, fig. 34). The extensor tendon process is fused without visible suture to the proximal part of the phalanx. Wing phalanges 1 and 2 are straight, whereas the distal end of wing phalanx 3 is slightly bent caudally.

Pelvic girdle

Pelvic plate. The pelvic plates are close to the sacral vertebrae and the hind-limb elements (Figs. 1 and 2). One of them preserves the postacetabular process of the ilium and the upper part of the caudal process of the ischium, which have a similar caudal length (Fig. 23A). The postacetabular process is short, low, and slightly recurved ventrally; it tapers slightly distally to a blunt end. The caudal process of the ischium is short and its upper part has a rounded end that is slightly recurved dorsally. Both processes are similar to those of the holotype of Austriadraco dallavecchiai (Fig. 23C). The postacetabular process is also like that of Carniadactylus rosenfeldi (MPUM 6009, which does not preserve the caudal process of the ischium). The caudal process of the ischium is unlike the trapezoidal and more elongated process of Peteinosaurus zambellii (Fig. 23D). The caudal margin of the pelvic plate is deeply concave in MFSN 21545; a very small dorsocaudal process of the ischium occurs in the middle of the concavity as in the pelvic plate of the holotype of Austriadraco dallavecchiai (Fig. 23C) and Peteinosaurus zambellii (Fig. 23D). The ilium and ischium appear to be fused to one other but the pelvic plate and the sacrum were not fused to each other.

A broad, plate-like bone is partially preserved close to the described pelvic plate and the sacral vertebrae (Figs. 2 and 16). It is possibly the cranial portion of the other pelvic plate. It has a straight and vertical cranial (pubic) margin as in other pelvic plates of Triassic pterosaurs (cf. Fig. 23C), and also a spatula-like cranial process that could be the preacetabular process of ilium. However, this process is shorter and morphologically unlike the preacetabular process of all other pterosaurs (e.g. Carniadactylus rosenfeldi, Dalla Vecchia, 2014, fig. 4.1.145; Austriadraco dallavecchiai, Fig. 23C; MCSNB 8950, Wild, 1994, fig. 5; Dimorphodon macronyx, Sangster, 2003, fig. 3.15; Dorygnathus banthensis, Padian, 2008a, figs. 14, 19C and 21; Campylognathoides liasicus, Wellnhofer, 1974, fig. 9; Campylognathoides sp., Padian, 2008b, fig. 9; and Rhamphorhynchus muensteri, Wellnhofer, 1975a, fig. 10). Its shape could therefore be apomorphic, if it actually is the preacetabular process of the ilium.

Prepubis. A prepubis (10.5 mm long) is partly covered by the postacetabular process of an ilium (Fig. 23A). The exact outline of the expanded prepubic blade cannot be seen. However, this prepubic plate is probably shovel-like with a prepubic blade slightly more expanded ventrally than dorsally (Fig. 23B) like that of E. ranzii (Fig. 23E).

Hind limb

Both right and left femora and tibiotarsi are partly preserved and the missing portions were restored (Figs. 1 and 2). Both femora are close and parallel to the corresponding tibiotarsi; both femur-tibiotarsus sets are close to one other and to the pelvic plates. No free tarsals can be identified. Only a few fragments are preserved of the elements of the foot.

Femur. The proximal third of the left femur (identified as such by its association with the left tibiotarsus) is preserved in cranial view, whereas the median third is missing and only a fragment remains of the distal third. The length of this preserved portion is 32 mm. In cranial view, the proximal head of the femur is dorsoventrally broad with only a hint of the neck (Fig. S7A). The angle between the proximal head of the femur and the shaft is 115°. The greater trochanter was damaged and has been reconstructed. Only a long and slightly sigmoidal portion of the shaft is preserved on the right femur. Because of the incompleteness of both elements, the exact total length of the femur cannot be known, but exceeds 32 mm.

Tibiotarsus and fibula. Right and left tibiotarsi are distinguished from one another on the basis of their position in the slightly disarticulated skeleton, the position of the associated fibula and the shape of their distal condyles (the lateral condyle is more developed than the medial one and projects more cranially than caudally in Triassic pterosaurs; Dalla Vecchia, 2003). Both tibiotarsi are strongly crushed and their shafts collapsed. The right tibiotarsus is exposed in caudal view and preserves the distal portion with the condyles (Fig. S7B) and fragments of most of the shaft with some fragments of the parallel and appressed fibula along the lateral side. The length of the preserved portion is 50 mm. The left tibiotarsus preserves the distal portion with the condyles and a proximal segment of the shaft. It is probable that it is exposed in medial view as the asymmetrical outline of the condyle (Fig. S7C) resembles that of the medial condyle of the left tibiotarsus of the holotype of Carniadactylus rosenfeldi (Dalla Vecchia, 2009a, fig. 9A; 2014, fig. 4.1.126 B-C); both elements also share a comma-like medial epicondyle. The proximal portion of the left tibiotarsus is covered by the blade of the left scapula, but part of its proximal end crops out from the ventral side of the blade where it is mostly concealed by vertebrae. The total length of the left tibiotarsus is approximately 55 mm.

Pes. Two phalanges and possibly a further two, all preserved close to the tibiotarsi (Figs. 1 and 2), belong to the completely disarticulated feet. The most complete phalanx is close to the left tibiotarsus and is short (4.9 mm) and stout.

Ontogenetic stage

MFSN 21545 is similar in size to the holotype of Carniadactylus rosenfeldi. It is slightly larger than the holotype of Austriadraco dallavecchiai and is nearly twice the linear size of the specimen MPUM 6009 of Carniadactylus rosenfeldi (Tables S1 and S3). MFSN 21545 is larger than specimens MCSNB 2887 and MCSNB 8950 and is much larger than the holotype of Arcticodactylus cromptonellus. Although the mean of the percent length of some selected skeletal elements of the holotype of E. ranzii is only 118% those of MFSN 21545 (Table S3), the latter appears much smaller when the fossils are compared (Fig. S8), because body mass is proportional to the length raised to the third power. MFSN 21545 is much smaller than the holotype of Raeticodactylus filisurensis.

The holotypes of Carniadactylus rosenfeldi and Austriadraco dallavecchiai are not juveniles, although the holotype of Austriadraco dallavecchiai shows some features of osteological immaturity (Dalla Vecchia, 2018). Osteological features of immaturity also occur in MPUM 6009 and MCSNB 8950 (Dalla Vecchia, 2018). The holotype of Arcticodactylus cromptonellus is a young individual, based on histological analysis (Padian, Horner & De Ricqlés, 2004). The holotype of E. ranzii is usually considered an adult, but it also shows some features indicating osteological immaturity (Dalla Vecchia, 2018). The holotype of Raeticodactylus filisurensis does not show any features of osteological immaturity (F.M. Dalla Vecchia, 2018, personal observation), but it is incomplete (e.g. pelvis and sacrum are not preserved).

Some features suggest osteological immaturity also for MFSN 21545. Roof and palatal elements of the skull are unfused. A suture is visible between the premaxillae. The mandibular rami are unfused at the symphysis (but see Dalla Vecchia, 2018). There are possibly three unfused distal carpals (but see Dalla Vecchia, 2009a, 2018). The ilium is not fused to the sacral ribs, which are not fused with the sacral vertebrae. Prepubes are not fused at the symphysis. On the other hand, the elements of the occipital region and basicranium appear to be fused, although is impossible to state whether the sutures among the elements were fully obliterated or not. The neural arches of the last dorsal vertebrae appear to be fused to their centra. The sternum is ossified with processes for the sternal ribs. Scapulae and coracoids are fused. There is a single proximal syncarpal. The extensor tendon of the first wing phalanx is fused to the phalanx (however, this occurred early during ontogeny in Triassic pterosaurs; Dalla Vecchia, 2018, contra Kellner, 2015). The phalanges of the manus are well-ossified with well-formed ginglymi. The ilium is fused with the puboischiadic plate and the sacral vertebrae are fused into a synsacrum. The fusion of the sacral vertebrae seems to have occurred relatively late during ontogeny in Triassic pterosaurs (Kellner, 2015; Dalla Vecchia, 2018). The rounded condylar end of the tibia indicates that it is actually a tibiotarsus with the proximal tarsals fused to the tibia. These features indicate that MFSN 21545 was not a juvenile, but probably was still growing when it died (Dalla Vecchia, 2018).

Systematic comparisons

Multicusped maxillary and mandibular teeth like those of Seazzadactylus venieri are reported only in the Triassic taxa E. ranzii, Carniadactylus rosenfeldi, Arcticodactylus cromptonellus and Austriadraco dallavecchiai (Dalla Vecchia, 2014). Caviramus schesaplanensis and Raeticodactylus filisurensis also have multicusped teeth, but their crowns are distinctly bulkier than those of Seazzadactylus venieri and have a peculiar constriction at their base (Dalla Vecchia, 2014, figs. 4.1.57A–C and 4.1.161B–C). Two other specimens (MCSNB 2887 and MCSNB 8950) do not preserve any trace of dentition, but they have been considered closely related to the taxa listed above in the literature (Wild, 1979, 1994). Seazzadactylus venieri must first be compared with specimens of Carniadactylus rosenfeldi because the holotype of this species comes from the same formation and geographic region (Dalla Vecchia, 2009a). Although both pterosaurs are from the Dolomia di Forni Formation, it cannot be known whether they are from the same stratigraphic level or not, as the exact stratigraphic provenance of MFSN 21545 is unknown and the fossiliferous part of the Dolomia di Forni Formation is about 500 m thick (Dalla Vecchia, 2006). The holotype of Carniadactylus rosenfeldi comes from a stratigraphically mid-low position within the Dolomia di Forni Formation (see Dalla Vecchia, 2014) and the boulder containing MFSN21545 was located in the lower part of the formation.

Significance of the new taxon

The addition of Seazzadactylus venieri to the matrix of Britt et al. (2018) caused a significative change in the topology of the strict consensus tree (Fig. 24) with respect to the original analysis (Britt et al., 2018, fig. 5). Austriadraco dallavecchiai and Arcticodactylus cromptonellus are nested within the same clade as Carniadactylus rosenfeldi, whereas they formed a separate clade in the strict consensus tree of Britt et al. (2018). Furthermore, E. ranzii is recovered as the basalmost taxon of the Lonchognatha and more derived than all other pterosaurs with multicusped dentition (which are all Triassic in age like E. ranzii). Therefore, E. ranzii would have developed its multicusped dentition independently or retained it as an ancestral feature. However, the latter hypothesis is less parsimonious because implies two steps more than the former.

The phylogenetic analysis supports the close relationships of Seazzadactylus venieri with Carniadactylus rosenfeldi and Austriadraco dallavecchiai, but also its separation as a distinct taxon within an unnamed clade of Triassic taxa also including Arcticodactylus cromptonellus and the trichotomy formed by MCSNB 8950, Caviramus schesaplanensis and Raeticodactylus filisurensis. Forcing Seazzadactylus venieri as the sister taxon of Carniadactylus rosenfeldi, the shortest topologies found are two steps longer than the non-forced shortest trees. Forcing Seazzadactylus venieri to be the sister taxon of Austriadraco dallavecchiai, the shortest topologies found are only one steps longer than the non-forced shortest trees. However, Austriadraco dallavecchiai is clearly distinct from Seazzadactylus venieri in the following features: a different maxillary process of the jugal; a stouter body of the jugal and the absence of the large foramen in the middle; a slit-like caudal part of the antorbital fenestra; the presence of an external mandibular fenestra; the presence of a constriction between the crown and ‘root’ in the premaxillary teeth; crowns of maxillary multicusped teeth that are much apicobasally higher than mesiodistally long; a different cuspidation pattern in the mandibular dentition; a narrower scapular blade; and distally diverging cranial and caudal margins of the shaft of the coracoid. These differences are not ontogenetic because the two holotypes appear to be at a similar ontogenetic stage (Dalla Vecchia, 2018). The potential for a sexually-dimorphic relationship between this trait disparity could only be tested with a larger sample, preferably from the same population.

It is premature to give a name to and a definition of the clade containing Seazzadactylus venieri, because the Bremer values for the nodes within it are low (Fig. 24). This instability is probably due to the non-overlapping known skeletal remains for many Triassic taxa, which are mostly represented by single and fragmentary specimens. Tree topology could change with the discovery of further specimens of the included terminal taxa. For this reason, all new specimens of Triassic pterosaurs are important. As in the analysis by Britt et al. (2018), MCSNB 8950 (lacking skull, mandible and teeth) acts as a wildcard taxon. When MCSNB 8950 is pruned from the analysis, the nodal supports of the least inclusive nodes containing Carniadactylus rosenfeldi and the Caviramus schesaplanensis + Raeticodactylus filisurensis clade are 2 and 7, respectively.

Unlike other pterosaurs, Seazzadactylus venieri has hexa- and heptacuspid tooth crowns and mesialmost multicusped teeth in the upper and lower jaws that have a different shape with respect to the following multicusped teeth. This confirms that the pattern of the multicusped dentition is quite variable among Triassic pterosaur taxa.

The peculiar shape of the pterygoid-ectopterygoid, which more resembles that of the theropod dinosaur Allosaurus than that of other non-monofenestratan pterosaurs, is puzzling. This apparent divergence highlights the need to describe these elements in greater detail in other pterosaurs. The peculiar shape of the pteroid confirms the diagnostic importance of this bone, which was already evidenced by Dalla Vecchia (2009a). The jugal also appears to have diagnostic importance within non-monofenestratan pterosaurs.

With the addition of Seazzadactylus venieri, the pterosaur genera and species from the Dolomia di Forni Formation increase to four (the others are Preondactylus buffarinii, Austriadactylus cristatus and Carniadactylus rosenfeldi). The two basal clades of the Pterosauria are represented in this sample (Fig. 24). The pterosaur diversity of the Dolomia di Forni Formation is higher than those of the Early Jurassic formations that have yielded relatively abundant pterosaur remains (e.g. the Blue Lias of England and the Posidonienschiefer of Germany; Barrett et al., 2008). However, this higher systematic diversity may be only apparent. The geological time-spans represented by the fossil-bearing part of the Dolomia di Forni Formation and the Liassic formations are probably different. The Dolomia di Forni Formation is dated to the Alaunian 3-Sevatian (late middle-late Norian) based on conodont biostratigraphy (Dalla Vecchia, 2014). The Dolomia di Forni Formation probably represents only a part of the Sevatian, but the durations of the Alaunian and Sevatian have not been precisely established (Olsen, Kent & Whiteside, 2011) and could be several million years (the duration of the entire Norian is ca. 18.5 million years according to Cohen et al., 2013). The fossiliferous part of the Dolomia di Forni Formation is hundreds of metres thick and the different pterosaur taxa come from different levels within it (Dalla Vecchia, 2014). In contrast, the range of Dorygnathus banthensis, Campylognathoides liasicus and Campylognathoides zitteli in the Posidonienschiefer corresponds to the Lias ε II/1–6 (Padian, 2008a, 2008b), which extends from about the middle of the Semicelatum to the lower third of the Elegans Ammonoid Subzones (Riegraf, Werner & Lörcher, 1984) and could correspond to less than 700 ky (Ogg, Ogg & Gradstein, 2008). Whereas Dorygnathus banthensis, Campylognathoides liasicus and Campylognathoides zitteli were probably coeval, the taxa from the Dolomia di Forni Formation may not have been.