Carcharias cuspidatus

Carcharias cuspidatus (Agassiz, 1843) Fig. 5A–N Lamna cuspidata Agassiz, 1843: 290. Material examined UNITED STATES OF AMERICA – Mississippi • 240 isolated teeth; Catahoula Formation; MMNS VP-6626 (168 teeth), MMNS VP-12053 (Fig. 5A–B), MMNS VP-12054 (Fig. 5C–D), MMNS VP-12055 (Fig. 5M–N), MMNS VP-12056 (Fig. 5E–F), MMNS VP-12057 (Fig. 5K–L), MMNS VP-12058 (Fig. 5I–J), SC 2013.28.272 to 28.283, SC 2013.28.284 (Fig. 5G–H), SC 2013.28.285 to 28.290, SC 2013.28.292 to 28.328, SC 2013.28.329 (10 teeth). Description Teeth can attain large sizes, with broken specimens estimated to have been more than 3 cm in total height. The tooth crown consists of a very large main cusp that is usually flanked by lateral cusplets. The main cusp may be mesio-distally narrow, tall, and labio-lingually thick or broadly triangular and labio-lingually thin. Cutting edges are smooth and may or may not extend to the base of the lateral cusplets. The labial face is flat to weakly convex, whereas the lingual crown face is more strongly convex. The crown enameloid is smooth. There is typically a single pair of lateral cusplets, although a poorly developed second cusplet may be present. Cusplets vary from small, narrow, and sharply pointed to low, very broad, and almost heel-like. Some specimens exhibit a denticulated morphology (Fig. 5K–L). Root lobes vary in shape and can be narrow and elongated or short and sub-rectangular, and lobes may be sub-parallel or widely diverging. The interlobe area is U-shaped but varies from deep and narrow to broad and shallow. A robust lingual protuberance may occur on the lingual root face, which is bisected by a narrow and long nutritive groove. Other lingual root surfaces have a more shelf-like appearance but also bear a conspicuous nutritive groove. Remarks Monognathic heterodonty is evident in our sample, with anterior teeth having a narrow main cusp with a sinuous profile. The mesial and distal cutting edges do not reach the base of the main cusp, the diminutive cusplets are narrow and pointed, and the root lobes are thin and elongated (Fig. 5A, M). There are variations in upper anterior tooth shape as, for example, demonstrated between the rather vertical crown and moderately diverging root lobes of the second upper anterior position (Fig. 5B) and the mesially curving crown and widely diverging lobes of the third anterior tooth (Fig. 5D). Upper lateral teeth (Fig. 5G–H, K–L) have a broader and labio-lingually thinner main cusp, the cutting edges are complete, and the lateral cusplets are low but very broad. Additionally, well-preserved specimens demonstrate that the root lobes are shorter, sub-rectangular and more divergent. With respect to dignathic heterodonty, the crowns of lower anterior teeth have a strong lingual curvature compared to those of upper anterior teeth, and the root lobes of upper anterior teeth are thicker, shorter, and more divergent compared to those of lower teeth (compare Fig. 5B to N). Additionally, upper lateral teeth are distally inclined, but those of the lower jaw are nearly vertical (compare Fig. 5G to I). Variations in overall tooth size within each tooth file are indicative of ontogenetic heterodonty, where smaller teeth (of juvenile individuals) are simply more gracile versions of larger (adult) teeth. A similar phenomenon was reported for Mennerotodus by Cicimurri et al. (2020). The teeth described above compare favorably to those of Carcharias cuspidatus, a species commonly reported from the Oligo-Miocene of North America and Europe (Baut & Génault 1999; Müller 1999; Purdy et al. 2001; Cappetta 2012; Reinecke et al. 2014). Over the past few decades, this species has variably been assigned to Carcharias (i.e., Purdy et al. 2001) and Araloselachus (see Cappetta 2012), with the most recent classification placing it within the former (Hovestadt 2020, 2022). Cappetta (2012) considered Araloselachus as distinct from Carcharias and other similar taxa, because teeth have smooth enameloid, anterior teeth have a less sigmoidal profile and “small and simple” (Cappetta 2012: 191) lateral cusplets, and lateral teeth have broad but low (sometimes) “pectinate” lateral cusplets. However, the crowns can be more-or-less sigmoidal depending on tooth position within a given jaw (i.e., upper versus lower, first anterior versus third anterior). Additionally, the presence or absence of crown ornamentation on teeth can be variable among individuals within a population of a given species (Purdy et al. 2001; Cicimurri et al. 2020). Furthermore, the “pectinate” lateral cusplets of lateral teeth, visible on some Catahoula Formation specimens (i.e., MMNS VP-12057), were also noted by Cicimurri et al. (2020) on Eocene Mennerotodus teeth. Purdy et al. (2001) provided some additional tooth characteristics that might prove useful in differentiating C. cuspidatus from C. taurus (Rafinesque, 1810), but the available sample does not allow us to test those criteria. Our observations regarding dignathic heterodonty are consistent with the work of Hovestadt (2020), who presented a reconstructed dentition of C. cuspidatus based on an articulated skeleton (pl. 7 figs 1–22), and familial assignment to Carchariidae is warranted.