Parotosuchus ptaszynskii, Sulej & Niedźwiedzki, 2013

Sulej, Tomasz & Niedźwiedzki, Grzegorz, 2013, A new large capitosaurid temnospondyl amphibian from the Early Triassic of Poland, Acta Palaeontologica Polonica 58 (1), pp. 65-75 : 68-71

Parotosuchus ptaszynskii sp. nov.

Figs. 3–7 .

Etymology: In honour of Tadeusz Ptaszyński, paleontologist and geologist, who collected the mandible and many other bones and footprints at Wióry.

Holotype: Posterior part of a mandible MPT. P 272 (compressed, with the postglenoid area bent ventrally).

Type locality: Wióry, southern Poland (Holy Cross Mountains region).

Type horizon: Wióry Formation, Late Olenekian, early Spathian (see Ptaszyński and Niedźwiedzki 2006; Niedźwiedzki and Ptaszyński 2007; Becker et al. 2007).

Referred material.—Skull fragment showing the dorsal side of the posterolateral part of the palate MPT.P 271.

Diagnosis.— Parotosuchus with the following combination of character states: torus arcuatus has more vertical position than the common condition in other parotosuchids. The dorsal surface of the retroarticular process is triangular, rather than roughly rectangular as in P. haughtoni and P. orenburgensis . The base of the hamate process is longer antero−posteriorly than in P. haughtoni and P. orenburgensis . The quadrate ramus of the pterygoid is shorter in length (= jaw articulation positioned more anteriorly) than in P. helgolandicus , P. nasutus , P. haughtoni , and longer than in P. orenburgensis . The lateral edge of the skull is more triangular in shape than in P. orientalis and P. nasutus .

Description

Skull

The general skull morphology is similar to that of Parotosuchus orenburgensis , especially the extremely strong curvature of the lateral edge of the interpterygoid fenestra. In all other Parotosuchus species this edge is much less concave, although the new material represents a larger skull than the holotype of P. orenburgensis (width of the skull PIN 951/42 is 315 mm while P. ptaszynskii is ~ 400 mm). The whole fenestra is wide and rather short (the shape of the palatine edge).

Ectoterygoid.—Although the small fragment of the left most posterior part of this bone is preserved, the lateral edge of the element in this region is clearly visible. The fact that the lateral edge is very strongly curved is an evidence that the skull was narrowing anteriorly and was not elongated as in most parotosuchids (e.g., Parotosuchus nasutus , P. helgolandicus , P. orientalis ).

Jugal.—The preserved part of processus alaris is massive and lay over the ectopterygoid.

Pterygoid.—The suture of the basipterygoid ramus with the parasphenoid is clearly visible in its anterior part. It seems that this ramus is relatively wide and results in a very blunt posterior end of the interpterygoid foramen. On its dorsal side there is a distinct pocket with vertical edge, which is directed antero−posteriorly. This appears to be the ventral edge of the recessus conoideus ( Bystrov and Efremov 1940). The quadrate ramus is rather long with its posterior end covered by the quadrate. The lateral edge of the quadrate ramus is directed strongly posteriorly making the medial edge of the temporal foramen strongly blunt. The palatine ramus is narrow and rather short, with a very distinct transverse flange. The medial edge of the palatine ramus is visible as an impression in the sandstone. At the base of this ramus a thin shelf protrudes anteriorly, disturbing the shape of the curvature of this margin (posterior edge of the interpterygoid foramen). The sutures with the ectopterygoid are partly visible.

http://dx.doi.org/10.4202/app.2011.0025

SULEJ AND NIEDŹWIEDZKI—EARLY TRIASSIC CAPITOSAURID FROM POLAND 71

prearticular crista articularis angular 10 mm

Palatine.—The medial edge of the palatine is visible as an impression in the sandstone. It is rather strongly concave in ventral view, very similar to Parotosuchus orenburgensis ( Fig. 4 ).

Quadrate.—The anterodorsal part of the quadrate is preserved lying over the quadrate ramus of the pterygoid. Its medial end forms a distinct edge with a vertical wall. This morphology was first described for Bentosuchus sushkini by Bystrov and Efremov (1940) as the incisura lateralis, but it is better illustrated by Howie (1970). The same structure was observed in Metoposaurus diagnosticus krasiejowensis by Sulej (2007). Lateral to the incisura lateralis, on the anterior side of the quadrate, a sutural facet faces anterolaterally. According to Howie (1970) it articulates with the prearticular process of the mandible. Howie (1970) described it in Stenocephalosaurus pronus as present on the pterygoid but, in the new material described here, it occurs on the anterior edge of the quadrate.

Quadratojugal.—The ventral edge of the bone is straight. The anterodorsal process is directed medially and overlies the quadrate anterodorsally.

Exoccipital.—The suture of the exoccipital with the parasphenoid is visible only in cross section (of the crista paroccipitalis of the parasphenoid and the dorsal part of the exoccipital). The whole occipital condyle is here visible in the CT scan ( Fig. 3B, C ). Its articular surface is directed posteroventrally and is approximately 15 mm wide mediolaterally.

Mandible

The specimen belongs to a larger individual (about 72 cm skull length) than that represented by the above described skull fragment (skull approximately 43 cm long). The oval Meckelian foramen is small and very short, and the torus arcuatus of the surangular has a very steep dorsal edge ( Fig. 5). The base of the hamate process is longer in lateral view in Parotosuchus ptaszynskii than in the holotype of P. orenburgensis . As preserved, the postglenoid area of P. ptaszynskii appears to be more deformed than that of P. orenburgensis . The retroarticular process is shorter than the glenoid area and its dorsal surface is sloped horizontally (character 47 in Maryańska and Shishkin 1996). The crista articularis is straight and horizontal in lingual view ( Fig. 6). The crista supraangularis which borders it labially is not so strongly convex in dorsal view as in P. orenburgensis ( Maryanska and Shishkin 1996: fig. 22) and P. haughtoni ( Damiani 2002: fig. 7 = Kestrosaurus dreyeri Shishkin et al. 2004 : fig. 5), but this difference may result from the state of preservation of the Polish specimen. The chorda tympani foramen is not visible. The crista articularis is distinct as in P. orenburgensis ( Maryańska and Shishkin 1996: fig. 22), but begins at the posterior part of the glenoid area as in P. haughtoni (= Kestrosaurus dreyeri ; Damiani 2002: fig 6). In P. orenburgensis it begins much more anteriorly (TS personal observation).

Figures

Fig. 3. Partial skull of capitosaurid amphibian Parotosuchus ptaszynskii sp. nov., Wióry, Late Olenekian, in a conglomeratic intercalation within a sandstone bed. A. Skull MPT.P 271 in dorsal view, coated with ammonium chloride. B. CT scan of the paroccipital process of the tabular and of the supraoccipital process of the postparietal. C. CT scan of the occipital condyle. D. Interpretative drawing.

Fig. 4. Skull reconstruction (ventral view) of capitosaurid amphibian Parotosuchus ptaszynskii sp. nov., Wióry, Late Olenekian (A) and comparison with Parotosuchus orenburgensis (Konzhukova, 1965), Rossypnaya, Ural River, Late Olenekian (C). The reconstruction of P. ptaszynskii sp. nov. based on the drawing of P. orenburgensis (from Konzhukova 1965); preserved fragment of P. ptaszynskii marked. B. Shadow of P. orenburgensis at the same scale as P. ptaszynskii in A.