Orthacanthus undetermined

Orthacanthus sp. (Fig. 2) MATERIAL. — A partially preserved isolated tooth (MHNT.PAL. 2023.9.1 [Fig. 2]). DESCRIPTION The tooth only preserves one of the two lateral cusps, the base of the medial cusp and a part of the basal tubercle. It has a preserved height of 12 mm from the base to the apex of the complete lateral cusp. The incomplete nature of the tooth makes it impossible to determine its orientation. The surface of the preserved cusps is smooth. The lateral cusp is slightly compressed labio-lingually and has a slightly curved dagger shape, with a slightly blunt apex. Serrations are present on both external cutting edges of the lateral cusp, with a denticle density of four denticles per mm. According to the basal diameter of the median cusp, its total high, when preserved, should not exceed a third of that of the lateral cusps. As the base of the tooth is broken, we are unable to determine the exact morphology of the basal tubercle. COMPARISONS A tricuspid tooth morphology is characteristic of Xenacanthiformes (e.g. Ginter et al. 2010). The genera Orthacanthus and Lebachacanthus Soler-Gijon, 1997 are characterised by labio-lingually compressed lanceolate lateral cusps and a reduced median cusp (Ginter et al. 2010). In Lebachacanthus, the lateral cusps of the side teeth are straight and pointed (Ginter et al. 2010), whereas in Orthacanthus, they have a blunt apex and a tendency to be slightly curved (Hampe 2003). MHNT. PAL. 2023.9.1 corresponds to an Orthacanthus tooth in terms of its blunt apex and the curvature of its lateral cusp. Unfortunately, it is too incomplete to be specifically identified, and is therefore referred here to Orthacanthus sp.