Galeocerdo platycuspidatum, Cicimurri & Ebersole & Stringer & Starnes & Phillips, 2025

Cicimurri, David J., Ebersole, Jun A., Stringer, Gary L., Starnes, James E. & Phillips, George E., 2025, Late Oligocene fishes (Chondrichthyes and Osteichthyes) from the Catahoula Formation in Wayne County, Mississippi, USA, European Journal of Taxonomy 984 (1), pp. 1-131 : 45-49

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 appear to be similar to those we show in Fig. 12G and I , and when compared to each other the G. mayumbensis teeth have a cusp that represents an average of 46% of total tooth width, whereas for G. platycuspidatum this proportion is 51%.

The temporal occurrence of the Catahoula Formation specimens is also older than the typically Miocene records of G. mayumbensis (see also Perez 2022). The Catahoula Formation teeth are similar to specimens that Müller (1999) identified as a new species, G. casei , from the Oligo-Miocene Belgrade Formation of North Carolina. However, this taxon has been placed in synonymy with G. mayumbensis ( Andrianavalona et al. 2015; Türtscher et al. 2021). Müller’s figured specimens ( Müller 1999: pl. 11 figs 1–4) have a mesio-distally narrow cusp closer to that of G. mayumbensis as opposed to G. platycuspidatum sp. nov. Only three of the four teeth shown by Müller (1999) are complete, and the cusp width of these specimens averages 42% of total tooth width, significantly lower than the average for G. platycuspidatum (51%).

Ebersole et al. (2024a) identified two teeth from the earliest Oligocene (lowermost Rupelian) Red Bluff Clay in Alabama as Galeocerdo sp. These teeth have compound serrations like those of G. platycuspidatum sp. nov., but the mesial cutting edge of the former is more evenly (and less) convex than on the latter. Additionally, the distal heel denticles of the Red Bluff Clay specimens are very large considering the relatively small tooth size, and the main cusp is narrower and more elongated compared to that of G. platycuspidatum . Ebersole et al. (2024a) postulated that the Red Bluff Clay teeth may represent an undescribed earliest Oligocene taxon, which is congruent with the hypothesis that Cenozoic tiger shark diversity is greater than presently recognized ( Türtscher et al. 2021).

Cicimurri & Knight (2009) and Cicimurri et al. (2022) reported teeth of Galeocerdo aduncus ( Agassiz, 1843) from the Chattian Chandler Bridge Formation and the Rupelian Ashley Formation, respectively, of South Carolina. The Catahoula Formation specimens differ significantly from the South Carolina specimens by attaining larger overall sizes, having greater overall crown height and a comparatively smaller but wider cusp, and the angle formed between the distal cutting edge and distal heel is obtuse. In contrast, this angle is 90º or less in G. aduncus , and the distal heel is clearly separated from the distal cutting edge by a distinct notch. Furthermore, the serrations of the Catahoula Formation Galeocerdo are larger and more complex compared to the South Carolina Oligocene teeth.

Galeocerdo capellini Lawley, 1876 is based on a single tooth, but if considered valid both this taxon and G. cuvier differ from G. platycuspidatum sp. nov. by having a mesio-distally narrower cusp, a less convex mesial cutting edge, and the distal angle is 90° or less.

Figures

Fig. 12. Galeocerdo platycuspidatum sp. nov., teeth. A–C. MMNS VP-6622.1 (paratype), anterior tooth. A. Labial view. B. Lingual view. C. Mesial view. D–E. MMNS VP-12052, symphyseal tooth. D. Labial view. E. Lingual view. F–G. MMNS VP-12049, anterior tooth. F. Labial view. G. Lingual view. H–J. MMNS VP-6622.2 (holotype), anterior tooth. H. Labial view. I. Lingual view. J. Mesial view. K–L. MMNS VP-6622.3, anterior tooth. K. Labial view. L. Lingual view. M–N. MMNS VP-6622.8, anterior tooth. M. Labial view. N. Lingual view. O–P. MMNS VP-6622.4, lateral tooth. O. Labial view. P. Lingual view. Q–R. MMNS VP-6622.7, lateral tooth. Q. Labial view. R. Lingual view. S–T. MMNS VP-12051, anterior tooth. S. Labial view. T. Lingual view. U–V. MMNS VP-6622.6, posterior tooth. U. Labial view. V. Lingual view. W–X. MMNS VP-6622.5, postero-lateral tooth. W. Labial view. X. Lingual view. Y–AA. MMNS VP-12050 (paratype), posterior tooth. Y. Labial view. Z. Lingual view. AA. Mesial view. Scale bars = 1 cm.