Pseudabdounia, Ebersole & Cicimurri & Stringer, 2019

Ebersole, Jun A., Cicimurri, David J. & Stringer, Gary L., 2019, Taxonomy and biostratigraphy of the elasmobranchs and bony fishes (Chondrichthyes and Osteichthyes) of the lower-to-middle Eocene (Ypresian to Bartonian) Claiborne Group in Alabama, USA, including an analysis of otoliths, European Journal of Taxonomy 585, pp. 1-274 : 88-90

Genus Pseudabdounia gen. nov.

urn:lsid:zoobank.org:act:AAB3C520-7C1D-4D10-9FB2-7DC604A27A57

Type species

Galeocerdo recticonus Winkler, 1874 , Eocene, Belgium.

Etymology

The genus name is composed of the Latin prefix ‘ pseud -’, meaning ‘false’ and the generic name Abdounia , defining a new genus for certain species formerly placed within Abdounia .

Diagnosis

Small teeth generally measuring less than 1.0 cm in mesiodistal width. Labial crown face flat to slightly convex; lingual face strongly convex. Main cusp triangular; erect on anterior teeth, distally inclined on lateral teeth. Apex of main cusp bi-convex. Lateral teeth with unique triangular outline in labial and lingual views. Three-to-eight mesial and distal cusplets present. Cusplets extend one-half to two-thirds the height of mesial and distal cutting edges. Cusplets often more in number mesially than distally. Cusplets triangular and largely united to main cusp. Cusplets decrease in size towards the crown base. Smooth mesial and distal cutting edge extends across main cusp and lateral cusplets. Anterior teeth taller than wide; lateral teeth often wider than tall. Root much higher lingually than labially. Deep nutritive groove on lingual root protuberance. Basal face of root flattened. Basal notch visible on some specimens. Root lobes divergent and rounded. Interlobe area shallow; U-shaped or V-shaped.

Remarks

Two species formerly placed within Abdounia , A. claibornensis ( White, 1956) and A. recticona (Winkler, 1874) are referred to this new genus. These two species appear related to the remaining members of Abdounia based on their root morphology, as they have a flat basal face, shallow interlobe area, basal notch on some specimens, deep nutritive groove, and divergent and rounded root lobes. These two taxa can be separated from the various Claibornian species of Abdounia by having three-to-eight mesial or distal cusplets (as opposed to no more than two pairs on Abdounia spp.) and by having lateral teeth with a unique triangular outline in labial and lingual views. The mesial and distal cusplets also extend much higher onto the main cusp than they do on any of the members of Abdounia . The two species placed into Pseudabdounia gen. nov. are discussed in detail below.

Pseudabdounia claibornensis ( White, 1956) gen. et comb. nov. Fig. 32 A–R

Galeorhinus recticonus claibornensis White, 1956: 148 , text-fig. 97, pl. 11, fig. 11.

Galeorhinus recticonus claibornensis – Thurmond & Jones 1981: 67 , fig. 11.

Abdounia claibornensis – Müller 1999: 48 , text-fig. 17, pl. 5, fig. 10–12.

Material examined

UNITED STATES OF AMERICA – Alabama • 89 isolated teeth; Claiborne Group ; ALMNH PV1993.2.396, ALMNH PV1993.2.397 (17 specimens), MSC 188.73 , MSC 188.88 , MSC 188.96 , MSC 188.1 , MSC 188.131 , MSC 188.185 , MSC 188.207 , MSC 188.245 , MSC 188.252 , MSC 188.258 , MSC 188.273 , MSC 188.276 , MSC 188.280 , MSC 35566.1 – 12 , MSC 37538, MSC 37563.1 – 33 , MSC 37564.1 – 2 , MSC 37570.1 – 2 , MSC 37591, MSC 37603, MSC 37611, MSC 37623.1 – 2 , MSC 37625, MSC 37626, MSC 38548 .

Description

Anterior teeth taller than wide or nearly equal in proportion, lateral teeth wider than tall. Teeth with broadly triangular crown; small central cusp flanked by four-to-eight cusplets; distal side usually with one cusplet more than mesial side. Main cusp of anterior teeth erect; distally inclined on lateral and posterior teeth. Cusplets triangular, divergent, decreasing in size towards crown base. Cutting edge of main cusp and cusplets smooth, continuous. Lingual crown face convex; labial face flat; enameloid smooth. Root bilobate with short, diverging lobes. Lingual attachment surface flat; wide and deep nutritive groove. Interlobe area on teeth shallow and U-shaped.

Remarks

White (1956) erected the subspecies Galeorhinus recticonus claibornensis based on an isolated tooth collected from the Gosport Sand in Monroe County, AL. Cappetta (1980a) later created the genus Abdounia for several species previously assigned to Scyliorhinus , including S. beaugei , S. biauriculatus , S. minutissimus , and S. enniskilleni , as well as Galeorhinus recticonus claibornensis . Based on his analysis of nine teeth from the upper Eocene Piney Point Formation in Virginia, Müller (1999) considered the claibornensis morphology distinct enough to elevate it to species status.

Within our sample of Claiborne teeth, those assigned to Pseudabdounia claibornensis gen. et comb. nov. appear very similar in overall gross morphology to teeth previously identified as Abdounia recticona . The teeth were differentiated by the number of pairs of lateral cusplets, with those assigned to A. recticona having three-to-four pairs and those of P. claibornensis gen. et comb. nov. having fourto-eight pairs. Although both species can have teeth with four pairs of lateral cusplets, teeth belonging to P. claibornensis gen. et comb. nov. can be differentiated by having smaller cusplets relative to the size of the main cusp. An argument could be made that the difference in number of cusplets could be a product of heterodonty, suggesting that teeth with narrower cusps with straight cutting edges are lower teeth, whereas teeth having a broader cusp with convex cutting edges are from the upper dentition. One might also suggest that anterior teeth may be those with fewer pairs of cusplets (three-to-four) that are arranged more in a horizontal row to the main cusp (giving them a T-shaped labial outline). Lateral teeth may be those with five or more cusplets that are oblique to the main cusp (triangular labial outline). However, the teeth in our Claiborne sample suggest that the difference in number of cusplets between P. claibornensis gen. et comb. nov. and the recticona morphology does not reflect heterodonty within a single species, as teeth from identical tooth positions (monognathic) and sizes (ontogenetic) have been recovered for both morphologies. Furthermore, the specimens in our Claiborne Group sample strongly suggests that the two species are stratigraphically separated, with P. claibornensis gen. et comb. nov. being confined to the Gosport Sand and the recticona morphology occurring within the stratigraphically older Tallahatta and Lisbon formations. The lack of stratigraphic overlap between these two species strongly suggests that the increase in pairs of cusplets is taxonomically significant and not related to intraspecific heterodonty. This, in turn, indicates that the two morphologies represent distinct taxa, further corroborating Müller’s (1999) elevation of the claibornensis morphology to species status.

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the basal Gosport Sand at site ACl-4 and the Gosport Sand at site ACl-15. Middle Bartonian, Zone NP17.

Figures

Fig. 32. Pseudabdounia claibornensis (White, 1956) gen. et comb. nov. and P. recticona (Winkler, 1874) gen. et comb. nov., teeth. A–R. P. claibornensis gen. et comb. nov. A–C. MSC 37591, anterior tooth, basal Gosport Sand. A. Labial view. B. Mesial view. C. Lingual view. D–F. MSC 37563.20, lateral tooth, basal Gosport Sand. D. Labial view. E. Mesial view. F. Lingual view. G–I. MSC 37563.16, lateral tooth, basal Gosport Sand. G. Labial view. H. Mesial view. I. Lingual view. J–L. MSC 188.88, lateral tooth, basal Gosport Sand. J. Labial view. K. Mesial view. L. Lingual view. M–O. MSC 37563.28, lateral tooth, basal Gosport Sand. M. Labial view. N. Mesial view. O. Lingual view. P–R. MSC 37563.30, lateral tooth, basal Gosport Sand. P. Labial view. Q. Mesial view. R. Lingual view. — S–JJ. P. recticona gen. et comb. nov. S–U. MSC 35767.1, lateral tooth, lower Tallahatta Formation. S. Labial view. T. Mesial view. U. Lingual view. V–X. MSC 37318.3, lateral tooth, basal Lisbon Formation. V. Labial view. W. Mesial view. X. Lingual view. Y–AA. MSC 37193, lateral tooth, Tallahatta/Lisbon formation contact zone, courtesy of T. Prescott Atkinson. Y. Labial view. Z. Mesial view. AA. Lingual view. BB– DD. MSC 37167.1, lateral tooth, Tallahatta/Lisbon formation contact zone, courtesy of James Lowery. BB. Labial view. CC. Mesial view. DD. Lingual view. EE–GG. MSC 35767.2, lateral tooth, lower Tallahatta Formation. EE. Labial view. FF. Mesial view. GG. Lingual view. HH–JJ. MSC 37167.2, lateral tooth, Tallahatta/Lisbon formation contact zone, courtesy of James Lowery. HH. Labial view. II. Mesial view. JJ. Lingual view. Scale bars: A–R = 5 mm; S–JJ=2 mm.