Galeocerdo platycuspidatum Cicimurri, Ebersole, Stringer, Starnes & Phillips, 2025, sp. nov.

Galeocerdo platycuspidatum sp. nov. urn:lsid:zoobank.org:act: AA878AB5-B515-4297-97B0-2902357D5FEC Fig. 12 Diagnosis The teeth of the new Oligocene species are distinguished by the combination of a very wide cusp with respect to crown width (cusp width comprises an average of 51% of total tooth width), a highly convex mesial cutting edge, a convex distal cutting edge, an obtuse distal angle (formed by the intersection of the distal cutting edge and distal heel), and a high distal heel (in lingual view) that is straight to only weakly concave. Of the six fossil species currently recognized, the teeth of the new taxon differ from the teeth of the Neogene Galeocerdo aduncus (Agassiz, 1843) by attaining larger overall sizes, having greater overall crown height and a comparatively smaller but wider cusp, and by having a more obtuse angle between the distal cutting edge and distal heel. Galeocerdo platycuspidatum sp. nov. teeth differ from those of the Neogene Galeocerdo capellini Lawley, 1876 by having a mesio-distally wider cusp, a more convex mesial cutting edge, and a distal angle of 90°. These teeth differ from the Eocene G. clarkensis White, 1956 by having a mesial swelling on the cutting edge (as opposed to being evenly convex), coarser serrations, and a wider distal angle (which is less than 90° in G. clarkensis). Galeocerdo platycuspidatum teeth are superficially similar to those of the Eocene G. eaglesomei White, 1955 but are easily separated by having compound (as opposed to simple) serrations. Finally, Galeocerdo platycuspidatum teeth can be differentiated from those of the Miocene G. mayumbensis Dartevelle & Casier, 1943 by having a wider cusp, a (generally) more convex mesial cutting edge, and a higher and less concave distal cutting edge. Etymology The species name alludes to the mesio-distally wide cusp with a rather flat labial face. Material examined Holotype UNITED STATES OF AMERICA – Mississippi • antero-lateral tooth; Catahoula Formation; MMNS VP-6622.2 (Fig. 12H–J). Paratypes UNITED STATES OF AMERICA – Mississippi • anterior tooth; Catahoula Formation; MMNS VP-6622.1 (Fig. 12A–C) • postero-lateral tooth; Catahoula Formation; MMNS VP-12050 (Fig. 12Y –AA). Other material UNITED STATES OF AMERICA – Mississippi • 43 isolated teeth; Catahoula Formation; MMNS VP-6622 (29 teeth), MMNS VP-6622.3 (Fig. 12K–L), MMNS VP-6622.4 (Fig. 12O–P), MMNS VP-6622.5 (Fig. 12W–X), MMNS VP-6622.6 (Fig. 12U–V), MMNS VP-6622.7 (Fig. 12Q–R), MMNS VP-6622.8 (Fig. 12M–N), MMNS VP-12049 (Fig. 12F–G), MMNS VP-12051 (Fig. 12S–T), MMNS VP-12052 (Fig. 12D–E), SC 2013.28.109 to 28.113. Stratum typicum Shelly, argillaceous sand of the Jones Branch fossil horizon, lower Catahoula Formation, Chattian Stage (horizon no longer accessible). Locus typicus Site MS.77.011, Jones Branch, tributary flowing into the Chickasawhay River, south of Waynesboro, Wayne County, Mississippi, USA. Description The teeth are broad-based and vary in overall height, with the largest specimens measuring up to 23 mm in mesio-distal width and 25 mm in apico-basal height. The labial crown face is virtually flat, but the lingual face is convex, and enameloid on both faces is smooth. In mesial view, the crown has a slight labial curvature. The basal one-half of the elongated mesial cutting edge can be convex (Fig. 12A), slightly concave (Fig. 12H), or nearly straight (Fig. 12F). However, the upper one-half to one-third of the mesial cutting edge is strongly convex and forms a conspicuous medial swelling (Figs 12O). This cutting edge is serrated, and the serrations are typically very coarse along the lower three-quarters of the cutting edges but become finer towards the crown apex (Fig. 12K). The distal cutting edge is much shorter, weakly convex but may be straight, usually lingually inclined but may be vertical, and serrated. The distal edge serrations are of the same size as or slightly smaller than those occurring on the apical portion of the mesial edge. The mesial and distal cutting edges converge apically to form a very broad, pointed cusp that is distally inclined to varying degrees. Serrations of both cutting edges extend virtually to the cusp apex. An elongated distal heel forms an obtuse angle with the distal cutting edge (i.e., Fig. 12I, T). The heel is oblique and can bear more than 12 denticles, which decrease in size towards the distal margin. The cutting edges on the denticles are serrated on the apical portion and often on the basal portion (i.e., Fig. 12D). The root is bilobate with sub-rectangular lobes that vary in length and degree of divergence. The lobes are separated by a deep V-shaped to shallow U-shaped interlobe area (compare Fig. 12G to R). Root lobe extremities may be rounded or pointed. A low lingual boss bears a long, wide, and shallow nutritive groove (Fig. 12K). Remarks Monognathic and ontogenetic heterodonty are evident in our sample based on jaws of extant Galeocerdo cuvier (Péron & Lesueur in Lesueur, 1822) that we examined (SC 2000.120.10, SC 2020.53.4, SC 2020.53.18, MSC 42597, MSC 42624). Teeth that are slightly asymmetrical represent symphyseal files (Fig. 12D–E). Specimens that are roughly as high as wide, have a somewhat angular to very convex mesial edge, and have a vertically oriented cusp are considered anterior teeth (Fig. 12A, K). Teeth that are more mesio-distally elongated, have a more convex mesial cutting edge, and have a strongly distally directed cusp are lateral teeth (Fig. 12O, Q). Overall, crown height decreases and cusp inclination increases towards the commissure (compare Fig. 12H, O, W, U). Some of the teeth in our sample (Fig. 12O) are comparable in size to those in the jaws of a 300 kg female of G. cuvier represented by SC 2000.120.10. Ontogenetic heterodonty is not only expressed as a difference in overall size among the teeth in our sample, but larger teeth of presumed adults have coarser serrations on the mesial cutting edge and more denticles on the distal heel compared to smaller (juvenile) teeth. Additionally, compound serrations are better developed on large teeth, with additional serrae occurring on the apical and basal edges of a serration, as opposed to only on the basal side on small teeth. A similar phenomenon was observed on the distal heel, where denticles of larger teeth bear serrae on the apical and basal edges of a denticle, but serrations are only on one edge of denticles on the smaller teeth. Galeocerdo teeth in the Catahoula Formation are characterized by the combination of coarse compound serrations on the mesial and distal cutting edges and a denticulated (with serrations) distal heel, features that are lacking on superficially similar teeth of Physogaleus, Galeorhinus, Hemipristis, and “ Sphyrna ” that occur in the Catahoula Formation. We also attempted to determine whether dignathic heterodonty was developed in the Catahoula Formation Galeocerdo. We observed slight dignathic heterodonty in the extant G. cuvier jaws we examined, and “broad-toothed” (upper) and “narrow-toothed” (lower) morphologies have been attributed to extinct G. aduncus (Agassiz, 1835) (i.e., Türtscher et al. 2021). For G. cuvier, we found that cusp width (measured from the base of the distal edge to the opposite side on the mesial edge, parallel to the labial crown foot) did not vary between upper and equivalent lower teeth. However, cusp length (measured along the distal cutting edge) on upper teeth was 1.5 mm to 2 mm longer than their lower counterparts. With respect to the Catahoula Formation Galeocerdo, the cusp width and height of all teeth measured varies slightly between 9 and 11 mm, and between 6 and 7 mm, respectively, and this overlap precluded the distinction of isolated upper teeth from lower teeth. However, the medial portion of the mesial cutting edge on extant G. cuvier upper anterior teeth is very convex, whereas the mesial edge of lower teeth is more uniformly convex. Our Catahoula Formation sample includes similar morphologies, and we believe that teeth like those shown in Fig. 12H, O, and F are upper teeth, whereas those shown in Fig. 12A, Q, and S are lower teeth. Six Galeocerdo species are recognized in the fossil record (including G. cuvier; Türtscher et al. 2021), and two of these, G. eaglesomei White, 1955 and G. clarkensis White, 1956, have been documented from Eocene strata in the Gulf Coastal Plain (Ebersole et al. 2019). Teeth of G. eaglesomei are superficially similar to those of Galeocerdo platycuspidatum sp. nov., but the latter have compound (as opposed to simple) serrations and a larger cusp. Although multiple authors identified other Eocene teeth from Alabama as G. latidens (see Tuomey 1858; Westgate 2001; Feldmann & Portell 2007; Clayton et al. 2013; Cappetta & Case 2016), this taxon is (at least in part) synonymous with G. eaglesomei (Ebersole et al. 2019; Türtscher et al. 2021). The mesial cutting edge on G. clarkensis teeth is more evenly convex, lacks a conspicuous medial swelling on the mesial cutting edge, and has finer serrations compared to the Catahoula Formation teeth. Additionally, the distal angle on G. clarkensis teeth is 90° or less, whereas the angle is obtuse on G. platycuspidatum sp. nov. teeth (except on postero-lateral teeth, where it is approximately 90°). The morphological features of Galeocerdo platycuspidatum sp. nov. teeth are like those of the Miocene G. mayumbensis Dartevelle & Casier, 1943, but examination of the type specimens originally figured (Darteville & Casier 1943: pl. 12 figs 22–29) indicates that the two are not conspecific. The cusp in Galeocerdo platycuspidatum is much wider, the mesial cutting edge is generally more convex, the distal cutting edge is usually convex, and the distal heel is higher but less concave compared to G. mayumbensis. Unfortunately, only two of the teeth shown by Dartevelle & Casier (1943: figs 25, 29) are complete and could be measured to determine the proportion of cusp width to tooth width. Those two teeth ap