Stethacanthus sp.

Ginter, Michał & Sun, Yuanlin, 2007, Chondrichthyan remains from the Lower Carboniferous of Muhua, southern China, Acta Palaeontologica Polonica 52 (4), pp. 705-727 : 710

Stethacanthus sp.

Fig. 3A–C .

Material.—10 teeth.

Description.—The stethacanthid teeth from Muhua are small (base width from 2 to 3 mm, median cusp height up to 2.5 mm) and display several features typical of Stethacanthus : separate bases of median and lateral cusps (this feature characteristic of all symmoriids); all the cusps rounded in crosssection at the base, only slightly compressed labio−lingually closer to the tip; dense but rather gentle striation of the cusps; compact and distinct articulation devices (orolingual button and basolabial projection) not wider than the base of the median cusp. The enameloid was removed from the crowns of the smaller teeth, but it remains on the larger, broken specimen, and an indistinct lateral carina is observable on the median cusp and on the outermost lateral cusp. The carina connects the lateral cusps, but apparently does not connect them with the median cusp. The teeth are generally five−cusped, but one of the smaller specimens was apparently four−cuspid ( Fig. 3A ), lacking one of the intermediate cusplets.

Remarks.—The most similar Stethacanthus teeth to those ones presented here are those associated with the spinebrush complex CMNH 8988 from the upper Famennian Cleveland Shale of Ohio. Williams (1985: pl. 15: 1) identified that specimen as S. altonensis (St. John and Worthen, 1875) , but it seems that he had too inclusive a concept of that species. The teeth of true S. altonensis (sensu Lund 1974; compare also “ Akmonistion zangerli ” in Coates and Sequeira 2001), characteristic of the Upper Mississippian, have a much stronger and rounded median cusp and relatively shorter outer cusps.

The teeth of Stethacanthus sp. from Muhua differ from the otherwise similar teeth of Denaea Pruvost, 1922 , by their shorter lingual bases, no sign of splitting of the button by the nutritive canal openings, and by their relatively thicker median cusp.

Figures

Fig. 3. Cladodont teeth from sample MH−1, middle Tournaisian of Muhua, China. A–C. Stethacanthus sp. A. PKUM02−0133 in lingual (A1) and labial (A2) views. B. PKUM02−0134 in labial (B1) and aboral (B2) views. C. PKUM02−0135 in labial (C1), lingual (C2), oral (C3), and lateral (C4) views. D–G. Tamiobatis sp. D. PKUM02−0136 in lingual (D1) and oral (D2) views. E. PKUM02−0137 in labial view. F. PKUM02−0138 in oral (F1) and lingual (F2) views. G. PKUM02−0139 in lingual view.