Diplodus undetermined

Diplodus sp. Fig. 28 Material examined UNITED STATES OF AMERICA – Mississippi • 183 isolated teeth; Catahoula Formation; SC 2013.28.643 (Fig. 28A–C), SC 2013.28.644 to 28.650, SC 2013.28.651 (Fig. 28D–F), SC 2013.28.652, SC 2013.28.653, SC 2013.28.654 (2 teeth), SC 2013.28.655 (11 teeth), SC 2013.28.656 (16 teeth), SC 2013.28.657 (20 teeth), SC 2013.28.658 (21 teeth), SC 2013.28.659 (20 teeth), SC 2013.28.660 (13 teeth), SC 2013.28.661 (37 teeth), SC 2013.28.662 (17 teeth), SC 2013.28.663 (15 teeth). Description Isolated teeth are highly laterally compressed (labio-lingually) and approximately as tall (apico-basally) as they are elongated (mesio-distally). The crown constitutes the upper two-thirds of a tooth and is covered with smooth enameloid. The labial crown face is weakly convex and the lingual face weakly concave (Fig. 28C, F). In mesial/distal view, the crown may be lingually curved. In labial/lingual view, unworn teeth have a roughly rhomboidal outline. The mesial margin may be uniformly convex or sinuous, with the basal portion being most convex but transitioning apically to concave. The distal margin is sinuous, with the basal portion being most convex but transitioning apically to concave. The apical part of the crown is formed into a cusp-like projection (Fig. 28B). The crown tapers basally towards a narrow bony projection, and the crown foot is marked by the enameloid boundary (Fig. 28E). Remarks Our sample includes teeth that are worn to varying degrees. These teeth demonstrate that the cuspidate crown apex exhibits the initial signs of in vivo wear (polished and somewhat flattened wear facet), and with continued use the cusp is worn completely away to a flat, relatively horizontal surface that reveals the internal dentine (compare Fig. 28A to D). Some teeth are worn nearly to the crown base, indicating a long period of tooth retention within the jaws and possibly pointing to a durophagous diet. Diplodus sp. was recently reported from the upper Rupelian Givhans Ferry Member of the Ashley Formation in Dorchester County, South Carolina by Cicimurri et al. (2022). These teeth are easy to distinguish from those of all other bony fishes by their laterally compressed crowns with sinuous anterior and posterior margins. Our Catahoula Formation teeth represent the first occurrence of this taxon from the Gulf Coastal Plain of the USA.