Pachyscyllium distans

Pachyscyllium distans (Probst, 1879) Fig. 9E–J Scyllium distans Probst, 1879: 170–171. Material examined UNITED STATES OF AMERICA – Mississippi • 11 isolated teeth; Catahoula Formation; MMNS VP-12048, SC 2013.28.116 (Fig. 9G–H), SC 2013.28.117 (Fig. 9E–F), SC 2013.28.118 to 28.124, SC 2013.28.125 (Fig. 9I–J). Description Very small teeth measuring up to 2 mm in total height and 1.5 mm in crown width. The crown consists of a main cusp that is typically flanked by a single pair of lateral cusplets. The main cusp ranges from narrow, tall, and vertical to broad, low, and distally inclined (depending on jaw position). The labial face of the main cusp is convex, and the crown foot is thickened such that it weakly overhangs the root. Additionally, the crown foot may be straight or weakly concave. The lingual face of the main cusp and lateral cusplets is also convex. The labial face bears vertical ridges that may extend to one-half the crown height (Fig. 9I); these ridges may occur across the entire labial face or may be restricted to the region below the lateral cusplets. The lingual face is generally smooth, but faint ridges may occur on the lateral cusplets. The lateral cusplets may be needle-like and extend up to one-third of the total crown height, or they may be low and broadly triangular. Smooth mesial and distal cutting edges extend along the main cusp and lateral cusplets. The bilobate root appears higher lingually than is apparent in labial view. Root lobes are very short and divergent, separated by a shallow and narrow interlobe area. The root is divided into very short, sub-triangular to teardrop-shaped lobes by an elongated nutritive groove (Fig. 9F, H). Remarks The available sample indicates that monognathic heterodonty was developed in this taxon. Anterior teeth have a rather narrow, tall, sharply pointed main cusp, and lateral cusplets are also tall and needle-like. Teeth believed to be from lateral files have a comparatively lower and broader main cusp that is distally inclined, and lateral cusplets are also shorter and broader (Fig. 9G–H). The main cusp appears to become more inclined the closer a tooth was located to the commissure. Most of the teeth in our sample exhibit one pair of lateral cusplets, but one specimen exhibits two cusplets on the mesial side (Fig. 9I–J). These diminutive teeth will not be confused with most other similarly shaped shark teeth found in the Catahoula Formation. The lone exception is another Pachyscyllium morphotype (see below), which differs from P. distans in several ways, the most conspicuous being the absence of crown ornamentation. Case (1980) documented P. distans from the Oligocene River Bend Formation of North Carolina. The species was apparently geographically widespread and temporally long-ranging, occurring in strata of Oligocene to Pliocene age in Europe (Reinecke et al. 2001, 2005, 2011, 2014; Collareta et al. 2020; Villafaña et al. 2020; Szabó et al. 2022).