Otodus (Carcharocles)

Otodus (Carcharocles) sp. Fig. 4 Material examined UNITED STATES OF AMERICA – Mississippi • 1 isolated tooth; Catahoula Formation; MMNS VP-6608. Description The specimen was broken upon recovery but has been repaired in its entirety, and it measures 6.2 cm in total height and 4.5 cm in width (mesio-distal). The tooth has a broadly triangular main cusp that is flanked by a pair of relatively small lateral cusplets. The main cusp is slightly distally inclined, and its labial face is flat, but its lingual face is convex, and the enameloid is smooth. In profile view, the main cusp is generally straight but slightly labially curved near the apex. The cutting edges are continuous along the main cusp and lateral cusplets. The mesial and distal cutting edges on the main cusp are somewhat concave at the lower half of the crown, but they become convex apically before converging to form a blunt apex. With respect to the lateral cusplets, the distal cutting edge is elongated and straight to weakly concave, whereas the mesial edge is very short and convex. The cusplets are rather small with respect to main cusp size, they occur very low on the crown, and they are differentiated from the main cusp by a deep notch (Fig. 4A). All cutting edges are serrated, but serration size and complexity vary along each cutting edge. Macroscopically, the serrations appear to be regular but under magnification larger or smaller individual serrae are scattered within lengths of more uniformly sized serrae. The apical and basal margins of individual serrae are sub-parallel, and serrae are separated from each other by deep notches. Some individual serrae are subdivided by one or two additional, smaller serrae. On the lateral cusplets, the serrations on the mesial edge are conspicuously finer than those on the distal edge. A wide, triangular dental band is located between the lingual crown foot and root (Fig. 4B). The root is massive, with rather short but robust mesial and distal lobes having rounded margins. The interlobe area is broadly U-shaped. A prominent lingual boss is perforated by nutritive foramina. Remarks Specimen MMNS VP-6608 appears to be an upper left tooth, possibly the second anterior, based on the width and slight distal inclination of the crown, as well as its relatively short root lobes (mesial lobe narrower and more pointed than the distal lobe) and broad U-shaped interlobe area (see also Gottfried & Fordyce 2001). Only one Catahoula Formation otodontid tooth is available to us, but the specimen is comparable to large examples of Otodus (Carcharocles) angustidens (Agassiz, 1835) identified from Oligocene deposits of Europe (i.e., Baut & Génault 1999; Reinecke et al. 2001, 2005). The Catahoula tooth differs from those in a sample of small Otodus (Carcharocles) teeth we examined from the Chattian Chandler Bridge Formation of South Carolina (SC 89.240 and SC 2006.1). These Chattian teeth were identified as Carcharocles sp. by Cicimurri & Knight (2009) and as Carcharodon subauriculatus (Agassiz, 1843) by Purdy et al. (2001). The rather broad but low lateral cusplets are not as well differentiated from the main cusp cutting edges compared to the Catahoula Formation tooth, a condition that is more similar to that of Otodus (Megaselachus) chubutensis (Ameghino, 1906). The Otodus (Carcharocles) subauriculatus morphotype is synonymous with O. (M.) chubutensis, and in fact Miocene specimens identified as Carcharodon subauriculatus by Purdy et al. (2001) have been reassigned to O. (M.) chubutensis (Perez et al. 2018). Although it is possible that the Chandler Bridge Formation teeth represent a transitional taxon between O. (C.) angustidens and O. (M.) chubutensis, this hypothesis is difficult to test with the single tooth in our sample. The otodontid taxa O. (C.) aksuaticus (Menner, 1928), O. (C.) auriculatus (de Blainville, 1818), O. (C.) sokolovi (Jaekel, 1895), O. (C.) angustidens, and O. (M.) chubutensis may represent a single lineage that culminates with Otodus (Megaselachus) megalodon (Agassiz, 1835) (Applegate & Espinosa-Arrubarrena 1996), but it is also possible that several otodontid lineages may have been present in the Paleogene (Cappetta 2012). The morphological criteria used to identify species can be ambiguous, as demonstrated above by the Catahoula Formation specimen (i.e., “regular” or “irregular” serrations) and within relatively small samples of teeth from one lithostratigraphic unit. Due to these factors, we herein only identified specimen MMNS VP-6608 to the generic level.