Alopias sp.

Alopias sp.

Fig. 5S–V View Fig

Material examined

UNITED STATES OF AMERICA – Mississippi • 2 isolated teeth; Catahoula Formation ; MMNS VP-7643 ( Fig. 5S–T View Fig ), SC 2013.28.271 ( Fig. 5U–V View Fig ).

Description

Specimen MMNS VP-7643 has a rather low but broadly triangular main cusp that is weakly distally inclined. In profile the crown is flat. The labial face is convex along the margins but concave medially, and there is a thickening at the crown foot. The lingual face is strongly and uniformly convex. Both crown faces have smooth enameloid. The mesial cutting edge is relatively straight, but the distal edge is weakly convex. Both cutting edges are smooth and extend basally onto short lateral shoulders. The mesial shoulder is more elongated but not well-differentiated compared to the distal heel. The bilobate root has rather short and highly diverging lobes with rounded extremities. The interlobe area is broadly U-shaped.

Tooth SC 2013.28.271 has a broad and very distally inclined cusp. The elongated mesial cutting edge is weakly convex apically and extends basally onto an elongated heel. The distal cutting edge is straight but transitions basally through a curved 90° angle onto a short distal heel. The cutting edges are smooth. The labial crown face is weakly convex and has a thickened crown foot. The distal face is more strongly convex, and the crown enameloid on both faces is smooth. The root is bilobate with short but highly diverging lobes that have rounded extremities. There is a conspicuous nutritive pore on a small lingual boss.

Remarks

Although different from each other, MMNS VP-7643 ( Fig. 5S–T View Fig ) and SC 2013.28.271 ( Fig. 5U–V View Fig ) both have broadly triangular crowns, smooth cutting edges that extend onto lateral shoulders, and root lobes with rounded extremities. These shared features lead us to conclude that they represent the same taxon and allow us to distinguish them from coeval Otodontidae and Carchariidae teeth in the Catahoula Formation.Additionally, these two teeth differ from aff. Pseudocarcharias sp. described above by having shorter but much broader crowns, non-cuspidate lateral shoulders, roots apparently lacking a nutritive groove, and lobes with rounded extremities.

Specimens MMNS VP-7643 and SC 2013.28.271 are comparable to teeth in an associated tooth set of extant Alopias vulpinus ( Bonnaterre, 1788) ( SC 2015.30.1) and within the jaws of an A. superciliosus Lowe, 1841 ( SC 202.53.12) that we examined. Tooth MMNS VP-7643 appears to represent an anterior jaw position, as it has a rather erect crown with only slight distal inclination ( Fig. 5S–T View Fig ). In contrast, the lower cusp height and greater distal inclination of SC 2013.28.271 indicate that it is from a more lateral tooth file ( Fig. 5U–V View Fig ). Neither specimen exhibits a nutritive groove, but this feature is not developed on some anterior teeth in SC 2015.30.1 ( A. vulpinus ). Additionally, the root of both specimens is abraded, and it is possible that these structures are simply not preserved. Teeth identified as Alopias aff. vulpinus in the German Chattian ( Reinecke et al. 2005: pls 21–22) appear to be more broad-based than the two Catahoula Formation specimens reported herein. The Catahoula Formation Alopias specimens have a much wider crown compared to the teeth of A. exigua ( Probst, 1879) , which have been reported from the Oligocene of Europe (i.e., Reinecke et al. 2001, 2005).

We note here the taxon Alopias latidens alabamensis White, 1956 that was based on teeth derived from upper Eocene (Priabonian) deposits in Alabama (Gulf Coastal Plain of the USA). Ebersole et al. (2019) determined that White’s taxon was a composite based on multiple taxa, with one being identified as Negaprion gilmorei ( Leriche, 1942) . Within the same volume, White (1956) erected the subspecies Alopias latidens carolinensis based on teeth derived from “phosphates” in South Carolina. Interestingly, White’s figured holotype ( White 1956: pl. 11 fig. 8) is quite similar to specimen SC 2013.28.271, and one might consider that the Catahoula Formation and South Carolina material are conspecific. However, the usage of Alopias latidens carolinensis for the Catahoula teeth is problematic because the type locality and precise stratigraphic occurrence and age of White’s syntypes are unknown, and material from the “phosphates” in South Carolina can range in age from the Eocene to Pliocene ( Cicimurri et al. 2022). We refrain from identifying the two teeth in our Catahoula Formation sample to species until a greater number of specimens are available for study.