Acanthocybium undetermined

? Acanthocybium sp. Fig. 25I–K Material examined UNITED STATES OF AMERICA – Mississippi • 3 isolated teeth; Catahoula Formation; SC 2013.28.577, SC 2013.28.578, SC 2013.28.579 (Fig. 23I–K). Description The teeth have a lanceolate profile. The anterior and posterior margins are formed into sharp smooth carinae, each of which extends from the tooth base and coalesces at a rounded apex (Fig. 25I). In anterior and posterior views, the crown is nearly vertical but has a slight lingual curvature, and the carina is located closer to the labial face (Fig. 25J). The lingual face is more convex than the labial face, particularly at the lower one-third. In basal view, the carinae are conspicuously differentiated from the main body of the crown due to the medially convex lingual face, and a deep pulp cavity is visible (Fig. 25K). Remarks These specimens differ from the lanceolate Sphyraena sp. teeth (see above) and from teeth assigned to Scomberomorus sp. (see below) by being much thicker labio-lingually and having much more convex labial and (especially) lingual faces. The Catahoula Formation teeth are comparable to those occurring in Acanthocybium premaxillae and a dentary (SC 2016.1.14) that we examined from the late Rupelian Ashley Formation of South Carolina. The premaxillary teeth of the Ashley Formation taxon are two to three times larger than those of the dentary, but the dentary teeth are equally convex labially and lingually. Based on these observations, the Catahoula Formation teeth were located in the premaxilla. The Catahoula Formation teeth are also similar to specimens identified as Palaeocybium from the Eocene of Alabama (Ebersole et al. 2019), as well as to the Oligocene Neocybium parvidentatum Monsch & Bannikov, 2012 of Europe (see also Leriche 1908). However, Palaeocybium possesses two rows of teeth in the jaws (Monsch 2005), which cannot be determined from the isolated teeth in our Catahoula Formation sample. To our knowledge, Palaeocybium is unknown beyond the Eocene. Jaws of Neocybium and the South Carolina Acanthocybium have only a single row of teeth, with those of the former perhaps being less convex and more widely separated in the jaws (Monsch & Bannikov 2012). We tentatively assign the Catahoula Formation specimens to Acanthocybium due to dental similarities between the Mississippi fossils and the South Carolina Oligocene Acanthocybium.