Aturobatis, Adnet, 2006

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 : 116-117

Aturobatis aff. A. aquensis Adnet, 2006

Fig. 41

Aturobatis aquensis Adnet, 2006: 111 , pl. 39, figs 3a–5b.

Material examined

UNITED STATES OF AMERICA – Alabama • 2 isolated teeth; Claiborne Group ; MSC 37687, MSC 38464 .

Description

Large teeth approaching 4.0 mm in mesiodistal width. Occlusal outline of crown is rhomboidal, wider than long, with sharp labial, lingual and lateral angles. Oral surface flat and diamond-shaped, subparallel to basal plane of crown. Sharp medial vertical ridge of labial face flanked by concave faces, with indistinct transverse ridge near the crown foot. Crown is weakly concave on each side of the vertical ridge. Lingual crown face slightly higher than labial face, inclined, straight, weakly concave on either side of lingual angle. Lingual crown foot developed into distinctive shelf-like projection, forming acute angle with lingual face. All crown faces smooth. Base of crown overhangs root labially and laterally. Root narrow, distally located under lingual part of crown, bilobed with a shallow medial nutritive groove. Root lobes rather elongate, with oblique labial face, extending just past lingual crown foot.

Remarks

The gross morphology of MSC 37687 and MSC 38464 is similar to other the Dasyatidae teeth in our sample, but the teeth are much larger and lack crown ornamentation.These teeth are also morphologically similar to the lateral teeth of members of the Myliobatidae , however, the lack of labial and lingual ornament on vertical crown faces and narrow, distally located root are inconsistent with our observations of Lisbon Formation Myliobatidae (see below). Teeth of Aturobatis are not to be confused with Hypolophodon , which has a weakly convex occlusal surface, much less angular appearance in occlusal and profile views, and a wide, centrally located root ( Dartevelle & Casier 1959; Murray et al. 2010: figs 2c–d; Cappetta 2012: fig. 412).

Adnet et al. (2010) and Cappetta (2012) mentioned the occurrence of Aturobatis in Ypresian strata in the Atlantic Coastal Plain of the USA, and a younger, potentially new species has been noted from the Priabonian of Morocco ( Adnet et al. 2010). Only the type species, A. aquensis , has been described and illustrated, and the two teeth in our Lisbon Formation sample, although much larger, are comparable to the Lutetian teeth reported by Adnet (2006). However, as A. aquensis is based on only four teeth and the range of variation is not known, we tentatively assign our two teeth to this species. Discovery of additional specimens will help determine if the Lisbon taxon is distinct or conspecific with A. aquensis .

Stratigraphic and geographic range in Alabama

The two specimens in our sample were collected from the basal Lisbon Formation at site ACov-11. Lower Lutetian, Zone NP15.

Figures

Fig. 41. Aturobatis aff. A. aquensis Adnet, 2006, teeth. A–D. MSC 37687, basal Tallahatta Formation. A. Orolingual view. B. Labial view. C. Oral view. D. Profile view. E–H. MSC 38464, basal Tallahatta Formation. E. Orolingual view. F. Labial view. G. Oral view. H. Profile view. Scale bars = 5 mm.