Lissodus sp.

Roelofs, Brett, Barham, Milo, Mory, Arthur J. & Trinajstic, Kate, 2016, Late Devonian and Early Carboniferous chondrichthyans from the Fairfield Group, Canning Basin, Western Australia, Palaeontologia Electronica (Barking, Essex: 1987) 262, pp. 1-28 : 18-19

Lissodus sp.

Figure 7.3-5

Material. One tooth from sample TS-1, Laurel Formation, Laurel Downs, Tournaisian.

Description. Asymmetrical tooth with an arched crown consisting of a high central cusp and a single, almost completely fused lateral cusp ( Figure 7.3 ). A broad, rounded labial peg extends labially from the centre of the crown base ( Figure 7.4 ). The crown is completely smooth, lacking any form of ornament. The base is labio-lingually narrow and extends lingually and distally beyond the crown base on one side. The crown overhangs a concave trough along the labial side of the base. The base has a row of large canal openings present on the lingual face with corresponding openings on the labial side ( Figure 7.5 ).

Remarks. This tooth possesses characters typical of the genus Lissodus , including a single central cusp, labial peg and lingually extended base, perforated by large vascular canals. In comparison to other Early Carboniferous Lissodus teeth figured in Duncan (2004), the crown is much higher, forming a more pointed apex. The basal features are also distinct, with a row of very large canals on the lingual face of the base and large canal openings along the baso-labial side. The aforementioned features also distinguish the tooth from other Early Carboniferous Lissodus teeth listed in Fischer (2008). A reconstruction of the dentition of Lissodus nodosus Seilacher, 1943 ( Duffin, 1985) and an interpretative reconstruction of Lissodus sp. by Duncan (2004) indicate a degree of variation among the tooth morphotypes. It is possible that the unusual features of the tooth described here may be a product of its position in the jaw.

The labial overhang of the main cusp and large canal openings on the base, present in the tooth here, are similar to the teeth of another Hybodont shark, Cassisodus margaritae Ginter and Sun, 2007 from Muhua, South China. The tooth however lacks a main diagnostic character of the genus Cassisodus , which is the presence of lingual and labial cusplets present on both faces of the crown. The possibility of wear or abrasion contributing to the lack of cusplets is unlikely as the crown retains a shiny enameloid surface.

Figures

FIGURE 7. Shark teeth from the Upper Devonian Gumhole Formation, Oscar Hill and Lower Carboniferous Laurel Formation, Laurel Downs, Lennard Shelf, Canning Basin, Western Australia. 1-2, Protacrodontidae gen. et sp. indet., WAM 15.6.29, sample OH-4, in lingual (1) and labial (2) views; 3-5, Lissodus sp., WAM 15.6.42, sample TS-1, in lingual (3), occlusal (4) and labial (5) views; 6-7, Hybodontoidea gen. et sp. indet., WAM 15.6.41, sample TS-1, in lingual (6) and labial (7) views; 8-11, Euselachii gen. et sp. indet.1, WAM 15.6.21, sample 198404, in lingual view (8), WAM 15.6.20, sample 198404, in occlusal view (9), WAM 15.6.27, sample 198404, in occluso-lingual view (10), and WAM 15.6.39, sample TS-1 in labial view (11); 12-13, Euselachii gen. et sp. indet. 2, WAM 15.6.40, sample TS-1, in occluso-lingual view (12) and WAM 15.6.22, sample TS-1, in labial view (13); 14-17, Holocephali gen. et sp. indet. 1, WAM 15.6.4, sample 198404, in occlusal view (14), and WAM 15.6.3, sample 198404, in lingual (15), labial (16) and occlusal (17) views. Scale bar length: 1-2, 0.5 mm; 3-5, 0.4 mm; 6-7, 0.75 mm; 8-10, 0.3 mm; 11, 1 mm; 12-13, 0.6 mm; 14-17, 5 mm.