Thrinacodus cf. gracia ( Grogan and Lund, 2008 )

Ginter, Michał, Duffin, Christopher J., Dean, Mark T. & Korn, Dieter, 2015, Late Viséan pelagic chondrichthyans from northern Europe, Acta Palaeontologica Polonica 60 (4), pp. 899-922 : 907

Thrinacodus cf. gracia ( Grogan and Lund, 2008)

Fig. 10F, G .

Material.—Three teeth from upper Asbian, Goniatites fimbriatus Ammonoid Zone, Westenfeld Quarry , Germany (sample C12); MWGUW/Ps/11/6–7.

Description.—In the sample from Westenfeld Quarry there occur three incomplete thrinacodont teeth, characterised by rather thick bases and thick cusps. The asymmetry of the crown is not spectacular; it is limited to the angle between the median and mesial cusps which is smaller than that between the median and distal cusp on the other side. The cusps are generally aligned, with a shallow depression in the basal/labial area below the median cusp.The cristae ornamenting the cusps are coarser than in T. dziki , but they look less coarse than in T. gracia . This, however, may be due to abrasion. Nothing can be said about the sigmoidality of the cusps, because in all three specimens the tips are broken. The same concerns the shape of the lingual part of the base which, in one of the better preserved specimens, is broken (uncovering a wide basal canal), and in the other is probably rounded by abrasion.

Remarks.—Despite the poor preservation it is evident that these teeth are more robust than those of T. dziki and do not display the lingually displaced median cusp and the basal/labial bulge, characteristic of the latter species. They are closer to the teeth of T. gracia which are known for their robustness and thickness of the base and the cusps. T. gracia is known thus far only from the Serpukhovian, so the teeth described here may belong to some earlier, but closely related form.

Stratigraphic and geographic range.— Thrinacodus gracia articulated specimens were recorded from the Serpukhovian of Bear Gulch, Montana, USA ( Grogan and Lund 2008); isolated teeth designated as T. cf. gracia are known from the Serpukhovian of the Moscow Syneclise, Russia (e.g., Ginter and Turner 2010: fig. 6F, G) and the upper Viséan of Rhenish Mountains, Germany (this paper). The identity of similar teeth from the upper Viséan of Fife, Scotland, UK ( Ginter and Turner 2010: fig. 4B) is uncertain.

Figures

Fig. 10. Chondrichthyan teeth from the upper Viséan of the Westenfeld Quarry, Rhenish Mountains, Germany. A–E. Denaea cf. fournieri Pruvost, 1922. A. MWGUW/Ps/11/1, in labial (A 1), lingual (A 2), and oral (A 3) views. B. MWGUW/Ps/11/2, in oral (B 1), lingual (B 2), and labial (B 3) views. C. MWGUW/ Ps/11/3, in oral view. D. MWGUW/Ps/11/4, in labial/aboral view. E. MWGUW/Ps/11/5, in lingual (E 1) and oral (E 2) views. F, G. Thrinacodus cf. gracia Grogan and Lund, 2008). F. MWGUW/Ps/11/6, in oral (F ) and lateral (F ) views. G. MWGUW/Ps/11/7, in lateral (G ) and oral (G ) views.