Cryptovenator hirschbergeri, Fröbisch & Schoch & Müller & Schindler & Schweiss, 2011

Fröbisch, Jörg, Schoch, Rainer R., Müller, Johannes, Schindler, Thomas & Schweiss, Dieter, 2011, A new basal sphenacodontid synapsid from the Late Carboniferous of the Saar-Nahe Basin, Germany, Acta Palaeontologica Polonica 56 (1), pp. 113-120 : 115-117

Cryptovenator hirschbergeri sp. nov.

Fig. 3 .

Etymology: Named after the county commissioner of Kusel, Dr. Winfried Hirschberger, for his untiring support of the Geoskop Urweltmuseum and of the scientific research in the Saar−Nahe Basin.

Holotype: LFN−PW 2008/5599− LS, an anterior right mandible fragment exposed in lateral view with 11 teeth and one empty socket ( Fig. 3 ).

Type locality: At the western rim of the Remigiusberg quarry (49 ° 54’88’’N, 7 ° 26’05’’E), about 1 km northeast of Haschbach in Rhineland Palatinate , Germany ( Fig. 1 ) .

Type horizon: Layer 26 of the Remigiusberg quarry profile ( Fig. 2 ), a dark, fine grained sandstone of the middle Remigiusberg Formation (300,0 Ma ±2.4 Ma), basal Rotliegend, upper Stephanian, late Gzhelian, latest Carboniferous.

Diagnosis.—A basal sphenacodontid synapsid autapomorphic in the shortness and robustness of the lower jaw with doi:10.4202/app.2010.0039

moderate heterodonty, including the absence of a greatly reduced first tooth and only a slight development of the second and third teeth into canines. Shares with Dimetrodon , Sphenacodon , and Ctenospondylus , but not Secodontosaurus , enlarged canines and a characteristic teardrop outline of the marginal teeth in lateral view, possession of a deep symphyseal region, and a strongly concave dorsal margin of the dentary.

Description.—Only approximately 40–50% of the mandible is preserved in the holotype of Cryptovenator hirschbergeri , including the symphyseal and mid−portion regions, containing 11 teeth and one alveolus. The specimen is partially imbedded in matrix and exposes a longitudinal section of the mandible in lateral view ( Fig. 3 ); the counterslab was not found. The labial sides of the teeth are slightly damaged, the only exception being the enlarged second tooth (canine), whereas the general outline is well preserved in almost all the teeth. An unusual feature of the mandible is not only the depth of the symphyseal region (more than two times the length of one canine and a feature characteristic of sphenacodontids), but also the fact that the depth of the mandible continues posteriorly to its broken margin. At the level of the fourth postcanine the mandible is almost as deep as at the symphysis. This morphology is similar to the condition in Dimetrodon grandis and D. limbatus ( Romer and Price 1940) , although it is even more pronounced in Cryptovenator . This suggests that the present taxon had a more robust mandible than all other known sphenacodontids, which clearly represents an autapomorphy. The preserved mid−portion of the mandible is markedly concave dorsally, a feature shared by all sphenacodontids, being most pronounced in the smaller species of the genus Dimetrodon , such as Dimetrodon natalis and D. milleri , as well as in Sphenacodon ( Romer and Price 1940; Eberth 1985).

The preserved anterior portion of the mandible is mainly composed of the dentary. However, as a result of its preservation as longitudinal section, the holotype mandible of Cryptovenator also exposes parts of the splenial and angular bones ( Fig. 3B ). The splenial makes up the posteroventral edge of the preserved mandible and exhibits on its lateral side an obvious facet for the dentary, which is broken off in this area. The exposure of the splenial at a level farther ventral than the dentary suggests that the splenial was likely visible near the symphysis in lateral view. The angular is positioned between the splenial ventrally and dentary dorsally, forming the medial and ventral walls of the Meckelian canal, comparable to the condition in Dimetrodon ( Romer and Price 1940: fig. 14). The broken posterodorsal edge of the mandible exhibits an additional element in cross−section on the medial side of the dentary that likely represents the anterior coracoid. The Meckelian canal is well exposed as a sedimentfilled hole in the centre of the mandible, being bordered by the angular medially and ventrally and the dentary dorsally and laterally. In addition, the symphyseal region of the lower jaw is strongly vascularised, as is typical for sphenacodontids ( Eberth 1985), being indicated by a large number of foramina and canals that are exposed in the longitudinal section of the anterior part of the dentary ( Fig. 3B ).

The dentition in the lower jaw of Cryptovenator clearly identifies this taxon as sphenacodontid synapsid, based on two main features: (i) the presence of enlarged canines, specifically the second and third dentary teeth, and (ii) the teardrop outline of the marginal teeth in lateral view. Nonetheless, Cryptovenator is autapomorphic in the development of moderate heterodonty only. This is expressed by the absence of a greatly reduced first tooth and only a slight development of the second and third teeth into canines. Heterodonty is much more pronounced in Sphenacodon , Ctenospondylus , and Dimetrodon , whereas it is absent in Secodontosaurus . There is a slight posteriad inclination of the two canines rather than being vertical, whereas the anteriormost dentary tooth is directed almost anteriad. The orientation of the anterior dentary teeth is variable in sphenacodontids, but an anteriad inclination is only known in Secodontosaurus , where it is, however, much more pronounced. In Cryptovenator the apices of all tooth crowns are recurved and the crowns are slightly bulbous above a somewhat constricted neck, resulting in the characteristic teardrop shape of sphenacodontid teeth. All teeth have mesial and distal cutting edges, but none bear serrations. Cutting edges are characteristic of a more inclusive group including Cutleria and Sphenacodontoidea, whereas serrations are known in some varanopids, ophiacodontids, therapsids, and the sphenacodontids Sphenacodon and Dimetrodon . A notable exception is Dimetrodon teutonis from the Lower Permian Tambach Formation of the Thuringian Basin in Germany, whose teeth have cutting edges but lack of serrations, as in Cryptovenator ( Berman et al. 2004) .

Stratigraphic and geographic range.— LFN−PW 2008/ 5599− LS is the holotype and only specimen of Cryptovenator hirschbergeri . It was collected from Layer 26 at the Remigiusberg quarry ( Fig. 2 ) about 1 km northeast of Haschbach in Rhineland Palatinate , Germany, which is part of the middle Remigiusberg Formation and corresponds to basal Rotliegend , upper Stephanian , late Gzhelian, latest Carboniferous in age .

Figures

Fig. 3. The holotype of Cryptovenator hirschbergeri gen. et sp. nov. (LFN−PW 2008/5599−LS), Remigiusberg Formation (Upper Carboniferous), Rhineland Palatinate, Germany. A. Photograph. B. interpretative drawing. C, D. Diagrammatic illustrations of skull of Dimetrodon grandis (C) and Cryptovenator hirschbergeri (D). E, F. Diagrammatic illustrations of isolated mandibles of Sphenacodon ferocior (E) and Dimetrodon grandis (F). C, E, F after Romer and Price (1940).

Fig. 1. Geological setting of the locality. A. Stratigraphic framework of the Rotliegend in the Saar Nahe Basin. B. Location of Saar−Nahe Basin (B1), geological map of the basin (B2), and location of the Remigiusberg quarry (B3). Lithostratigraphy follows Schindler (2007); isotopic ages after Burger et al. (1997), Königer et al. (2002), and Lippolt and Hess (1989); position of the Permo−Carboniferous boundary (299.0 ±0.8 Ma) is based on Ogg et al. (2008).

Fig. 2. Lithological column of the Remigiusberg quarry, arrow marks the horizon (layer 26) of the holotype of Cryptovenator hirschbergeri.