Discosauriscidae, ROMER, 1947

Klembara, Jozef D., 2016, A New Find Of Discosauriscid Seymouriamorph From The Lower Permian Of Boskovice Basin In Moravia (The Czech Republic), Fossil Imprint 72 (1 - 2), pp. 117-121 : 118-120

Discosauriscidae indet.

M a t e r i a l. DE K 396, skull and anterior portion of the postcranial skeleton, is the only known specimen and is deposited in the Department of Ecology, Faculty of Natural Sciences, Comenius University in Bratislava, Slovakia.

L o c a l i t y a n d h o r i z o n. Boskovice Basin in Moravia (the Czech Republic); Kochov-Horka, western margin of the town Letovice ( Klembara and Meszároš 1992). Middle Letovice Formation, Autunian, Lower Permian ( Zajíc and Štamberg 2004).

D i a g n o s i s. Autapomorphies relative to discosauriscids Discosauriscus , Makowskia , Spinarerpeton and Ariekanerpeton include: 1) strong vermiculate ornamentation of the skull roof bones; 2) intertemporal larger than the supratemporal; and 3) a small process of parietal lying between the postfrontal and intertemporal is missing, thus the anterolateral margin of the parietal is long and almost straight.

D e s c r i p t i o n. The bones of the skull roof are massively constructed and the sutures between them are mostly simple ( Text-fig. 1a ). The shape of any given bone may differ on the left and right sides. The ornamentation of all bones is conspicuously developed. It consists of high ridges of different lengths and course, and deep grooves and pits. Such ridges form a pronounced polygonal pattern. Due to this strong ornamentation, the ossification centres are not clearly recognizable. Deep lateral line canals are present on the left intertemporal and postfrontal and right postfrontal and postorbital.

The frontal is a mediolaterally narrow bone and is longer then the parietal ( Text-fig. 1a, b ). The prefrontal has a long posterior process and it joins the long anterior process of the postfrontal at a level slightly anteriorly to the mid-length of the frontal. The prefrontal, postfrontal and postorbital bear sharp orbital margins. The orbital margin is highest on the right postorbital. The right postorbital is of triradiate shape; the posterior process is the shortest and fits between the intertemporal and squamosal ( Text-fig. 1a, b ). The postorbital is subdivided; there is a small, independent bone, lying within the territory of the posteromedial portion of postorbital 1 (designated as postorbital 2 here, Text-fig. 1a ). The lateral end of the postorbital is pointed.

The anterior portion of the left parietal is mediolaterally wider than that of the right parietal; however, it is opposite in the posterior portion of the parietal ( Text-fig. 1a ). The anterolateral margin of the parietal is long and almost straight (only very shallowly concave). It has a long suture with the intertemporal but only a very short one with the postfrontal. On the right side, the parietal-postfrontal suture is slightly longer. The pineal foramen is rounded and not closed by the parietals anteriorly. Posteriorly to the pineal foramen, the suture between the parietals is straight. The left intertemporal is a large pentagonal-shaped bone, and is larger than the left supratempotal. The right intertemporal has an approximately oval shape. As preserved, the right intertemporal is mediolaterally compressed and dorsally vaulted, giving the impression that it is smaller than the supratemporal in dorsal view. However, its reconstruction shows it is larger in size than the right supratemporal ( Text-fig. 1a, b ). There is a small oval bone present between the right prefrontal and intertemporal bones ( Text-fig. 1b ). Such small bones, lying within the territory of the given bone or between the territories of two or three bones, are quite common within the skull roof bones of discosauriscisds ( Klembara 1993, Klembara et al. 2002). The posterior portion of the right intertemporal extends into a small process fitting into the anterior portion of the supratemporal. The supratemporal is quadrangular. Its suture with the parietal is slightly shorter than the intertemporal-parietal suture.

The tabulars and postparietals are mediolaterally elongated. The tabular process is of quadrangular shape and extends posteriorly from the ventral surface of the tabular. The tabular occipital flange is orientated posteroventrally and has a smooth dorsal surface. It joins medially the slightly smaller occipital flange of the postparietal. The tabular has a suture with the parietal.

Approximately only the posterior half of the right maxilla is preserved. On its internal surface, the supradental shelf and several teeth are observable. The teeth are conical, slightly posteriorly curved and their basal portions bear dorsoventral grooves. The tooth crowns have medial and distal cutting edges.

C o m p a r i s o n s. So far, three genera and four species belonging to the family Discosauriscidae (Seymouriamorpha) have been described from the Lower Permian localities of the Boskovice Basin in Moravia (the Czech Republic):

1) Discosauriscus austriacus ( MAKOWSKY, 1876)

2) Discosauriscus pulcherrimus ( FRITSCH, 1880)

3) Makowskia laticephala KLEMBARA, 2005

4) Spinarerpeton brevicephalum KLEMBARA, 2009a.

The fifth species belonging to Discosauriscidae is Ariekanerpeton sigalovi ( TATARINOV, 1968) from the Lower Permian of Tadzhikistan ( Klembara and Ruta 2005a, b).

Among the discosauriscids, the skull of DE K 396 is most similar to that of Discosauriscus austriacus ( Text-fig. 1c ). The specimen DE K 396 can be distinguished from all other species of Discosauriscidae by the following features:

Distinct ornamentation of the skull roofing bones. The ornamentation consists of high and mostly sharp ridges joined together forming a polygonal pattern. Such distinct ornamentation is developed neither in the similar-sized specimens of Discosauriscus austriacus , nor in the largest known specimens of D. austriacus (with the skull length up to about 62 mm; Klembara 1995, 1997, 2009a, b). The degree of ossification and the type of sutures on the skull roof bones of DE K 396 correspond to those of the similar-sized specimens of Discosauriscus austriacus ( Klembara 1995, 1997).

The intertemporal is larger than the supratemporal. This is in contrast to all other seymouriamorphs ( Klembara 2009a).

A small process of the parietal fitting between the postfrontal and intertemporal is absent. As a consequence, the anterolateral margin of the parietal is long and almost straight. This is clearly observable on both parietals. Such parietal morphology is not present in any known seymouriamorph.

R e c o n s t r u c t e d s k u l l. Although several bones of the skull roof are missing, it was possible to make a reconstruction at least in dorsal view ( Text-fig. 1b ).The skull is about as long as it is wide. It has a semi-elliptical shape with the long axis along the mid-line. The preorbital portion is short. The orbits are anteroposteriorly elongated and oval. They lie in the posterior portion of the anterior half of the skull length; only their posterior-most parts extend posterior to the mid-length of the skull. The prefrontal-postfrontal suture is short and lies slightly anteriorly to the mid-length of the frontals. The pineal foramen lies at the level of the anterior halves of the intertemporals and slightly posteriorly to the level of the posterior margins of the orbits. The anterior portions of both parietals are mediolaterally narrow due to the large size of the intertemporals. The intertemporal is larger than the supratemporal. The jaw joint lies at the level of the tabular. The otic notch is anteroposteriorly deep, similar to that in Discosauriscus ( Klembara 1997) , but not as deep as in Spinarerpeton KLEMBARA, 2009a ( Klembara 2009a) .

C o n c l u s i o n s. Although the specimen DE K 396 is not yet fully prepared, its skull morphology clearly exhibits several features absent not only in Discosauriscus , but also in other species of Discosauriscidae . Thus, it likely represents a new taxon. If so, this taxon will probably belong to Discosauriscidae , because the skull of DE K 396 exhibits three of the four distinguishing features of Discosauriscidae (see the above Diagnosis). The taxonomic resolution of DE K 396 is pending its full preparation.

Figures

Text-fig. 1. a – Discosauriscidae indet., DE K 396, skull in dorsal view. b – reconstruction of skull of DE K 396 in dorsal view. c – reconstruction of skull of Discosauriscus austriacus in dorsal view (on the basis of specimen Z 15529 from the locality Kochov-Horka, Boskovice Basin, deposited in the Slovak National Museum, Bratislava, Slovakia; Klembara 1997).