Pseudaetobatus belli Cicimurri & Ebersole, 2015

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 : 133-135

Pseudaetobatus belli Cicimurri & Ebersole, 2015

Fig. 49

Pseudaetobatus belli Cicimurri & Ebersole, 2015: 5 , figs 4–5.

Material examined

UNITED STATES OF AMERICA – Alabama • 225 isolated teeth; Claiborne Group ; MSC 33278, MSC 33306, MSC 33311, MSC 33320, MSC 33328, MSC 33338, MSC 33361, MSC 33389, MSC 33412, MSC 33413, MSC 33422, MSC 33430, MSC 33433, MSC 33444, MSC 33449, MSC 33455, MSC 33461, MSC 33475, MSC 33507, MSC 33511, MSC 33520, MSC 33525, MSC 33587, MSC 33643, MSC 33682, MSC 33685, MSC 33688, MSC 33693, MSC 33729, MSC 33858, MSC 33943, MSC 35032, MSC 35048, MSC 35049, MSC 35050, MSC 35051, MSC 35052, MSC 35052, MSC 35053, MSC 35054, MSC 35055, MSC 35056, MSC 35058, MSC 35059, MSC 35060, MSC 35061, MSC 35062, MSC 35063 (13 specimens), MSC 35064, MSC 35065, MSC 35066, MSC 35067, MSC 35068, MSC 35069, MSC 35070, MSC 35071, MSC 35073, MSC 35074, MSC 35075, MSC 35078, MSC 35080, MSC 35081, MSC 35082, MSC 35083 (13 specimens), MSC 35749 (8 specimens), MSC 37058 (90 specimens), MSC 38880 (28 specimens), SC 2017.32.1–11 (11 specimens) .

Description

Median teeth wide and six-sided. Tooth crown thick with rectangular outline in cross section. Upper median teeth straight to weakly sinuous. Lower median teeth arcuate; distal ends of crown directed lingually (labially convex crown margin). Labial and lingual crown faces ornamented with fine vertical wrinkling. Labial face overhangs the root; has shallow basal transverse groove. Groove articulates with thick and rounded lingual transverse ridge located at the crown base. Tooth root polyaulocorhize; subdivided into thin lamellae by numerous nutritive grooves; root extends well beyond lingual crown base. Two lateral tooth morphologies have been identified. First has six-sided crown that is slightly wider than long, has sharp mesial and distal angles. Second has angular mesial margin but downturned, distally directed and pointed distal margin. Crown ornament and root morphology similar to median teeth.

Remarks

Pseudaetobatus was recently formally recognized in North America by Cicimurri & Ebersole (2015), and two species were identified. Pseudaetobatus belli occurs in lower-to-middle Eocene deposits of the Hatchetigbee and Tallahatta formations of Alabama and Mississippi, whereas P. undulatus is known only from the upper Eocene Dry Branch Formation of South Carolina ( Cicimurri & Knight 2019). Within the Tallahatta Formation, Pseudaetobatus occurs with Aetomylaeus , Myliobatis , and Rhinoptera , but median teeth are easily separated from those of Aetomylaeus by their weak wrinkling on the labial and lingual faces and thick, rounded lingual transverse ridge. The teeth of Rhinoptera lack the very elongated, lingually directed root lobes seen on teeth of Pseudaetobatus . Myliobatis teeth have concave labial and convex lingual faces, which are lingually inclined, and have coarser vertical wrinkling. Additionally, the lateral-most teeth of Pseudaetobatus are distinguished by their downturned, sweptback and pointed distal margin. With respect to this lateral tooth morphology, those interpreted to have been part of a lower dentition are slightly wider than those in the upper dentition.

Pseudaetobatus is not known from the Lisbon Formation, where it seems to have been supplanted by Aetobatus . These two genera could theoretically be present in the same deposit, and it would be difficult to distinguish the median teeth of these two taxa. However, there are no lateral teeth in the Aetobatus dentition, and the distal ends of median teeth are downturned and swept distally. In contrast, the distal ends of Pseudaetobatus median teeth are angular and exhibit an attachment surface for articulation with a lateral tooth.

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the Meridian Sand Member of the Tallahatta Formation and lower Tallahatta Formation at site ADl-1. Upper Ypresian to lower Lutetian, zones NP12 to NP14.

Figures

Fig. 49. Pseudaetobatus belli Cicimurri & Ebersole, 2015, teeth. A–E. MSC 35048, holotype, lower median tooth, lower Tallahatta Formation. A. Oral view. B. Basal view. C. Labial view. D. Lingual view. E. Profile view. F–K. MSC 35054, paratype, lower right distal–most lateral tooth, lower Tallahatta Formation. F. Oral view. G. Basal view. H. Labial view. I. Lingual view. J. Distal view. K. Mesial view. L–P. MSC 35058, paratype, upper? median tooth, lower Tallahatta Formation. L. Oral view. M. Basal view. N. Labial view. O. Lingual view. P. Profile view. Q–V. MSC 35059, paratype, upper right distalmost lateral tooth, lower Tallahatta Formation. Q. Oral view. R. Basal view. S. Labial view. T. Lingual view. U. Distal view. V. Mesial view. W–BB. MSC 35062, paratype, intermediate lateral tooth, lower Tallahatta Formation. W. Oral view. X. Basal view. Y. Distal view. Z. Mesial view. AA. Labial view. BB. Lingual view. Scale bars = 1 cm.