Physogaleus undetermined

Physogaleus sp. Fig. 7 EE–II Material examined UNITED STATES OF AMERICA – Mississippi • 14 isolated teeth; Catahoula Formation; SC 2013.28.134 (Fig. 7 EE–GG), SC 2013.28.135, SC 2013.28.136 (Fig. 7 HH–II), SC 2013.28.137 to 28.143, SC 2013.28.144 (4 teeth). Description The teeth are small, measuring up to 6 mm in mesio-distal width and less than 5 mm in apico-basal height. The crown consists of a prominent cusp and a distal heel. The elongated mesial cutting edge of the cusp is sharp and smooth (Fig. 7 HH), but weak denticulation occurs at the base of the edge on SC 2013.28.134 (Fig. 7 EE). The mesial edge ranges from straight, to sinuous, to weakly convex or weakly concave (Fig. 7 FF, II). The distal cutting edge is also smooth but much shorter and may be vertical to distally inclined. The mesial and distal edges intersect apically to form a sharp apex. The distal heel is low and bears two or three denticles. These denticles decrease in size distally, and the distal-most denticle is very inconspicuous. The labial crown face is smooth and flat, whereas the lingual crown face is smooth and convex (Fig. 7 JJ). The root is bilobate, with elongated, highly divergent sub-rectangular lobes that are separated by a broad V-shaped interlobe area. The teeth have a thin, medially located lingual nutritive groove (Fig. 7 FF, II). Remarks Our small sample appears to reflect monognathic and dignathic heterodonty within the dentition of this taxon. Anterior teeth are mesio-distally narrower than lateral teeth, and the cusp of anterior teeth is more erect. Additionally, the main cusp becomes more inclined towards the jaw commissure. The distal heel of lateral teeth is more horizontal than that of anterior teeth, and it is more elongated, with a greater number of denticles. Teeth that we believe are from the lower dentition have a narrower main cusp with a more concave mesial cutting edge (Fig. 7 HH) compared to upper teeth (Fig. 7 EE). These teeth differ from those of Physogaleus contortus and Galeocerdo from the Catahoula Formation by lacking serrated mesial and distal cutting edges. Additionally, they can be separated from the teeth of Rhizoprionodon and Sphyrnidae (see below) by having denticles at the base of the mesial cutting edge and on the distal heel. Ebersole et al. (2021) reported a single Physogaleus sp. tooth from the Glendon Limestone Member of the Byram Formation (NP23) in southwestern Alabama that is comparable to the Catahoula Formation material. Cicimurri et al. (2022) later reported two specimens from the Rupelian Ashley Formation of South Carolina that they considered to be conspecific with the Physogaleus sp. specimens previously documented by Cicimurri & Knight (2009) from the Chattian Chandler Bridge Formation in South Carolina. The Catahoula Formation sample is younger than the Alabama occurrence and bracketed in age by the two South Carolina Oligocene occurrences, but it is possible that all the material is conspecific. Although the Catahoula Formation sample is rather small and imperfectly preserved, the teeth appear to differ from those of Eocene P. secundus (Winkler, 1874) by the weakly crenulated lower portion of their mesial cutting edge and the poorly developed distal heel denticles. They also differ from the Eocene P. alabamensis (Leriche, 1942) and Oligocene P. latus (Storms, 1894) by their smaller size and poorly developed mesial cutting edge and distal heel denticles (Reinecke et al. 2014; Ebersole et al. 2019). Larger samples from both the Gulf and Atlantic coastal plains are necessary to make more precise comparisons and identifications of the Oligocene Physogaleus sp. teeth.