Myliobatis sp. 1, Cuvier, 1816

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 : 129-130

Myliobatis sp. 1

Fig. 47 A–J

Material examined

UNITED STATES OF AMERICA – Alabama • 312 isolated teeth; Claiborne Group ; MSC 33262, MSC 33293, MSC 33294, MSC 33317, MSC 33319, MSC 33332, MSC 33344, MSC 33345, MSC 33347, MSC 33350, MSC 33351, MSC 33362 (2 specimens), MSC 33363, MSC 33366, MSC 33394, MSC 33396, MSC 33402, MSC 33420, MSC 33471, MSC 33496, MSC 33529, MSC 33536, MSC 33573, MSC 33655, MSC 33672, MSC 33677, MSC 33865, MSC 33878, MSC 33883, MSC 33904, MSC 33913, MSC 33915, MSC 33925, MSC 33928, MSC 35747 (6 specimens), MSC 35748 (4 specimens), MSC 35751 (3 specimens), MSC 38881 (222 specimens), MSC 38937 (7 specimens), MSC 38938 (15 specimens), MSC 38940 (16 specimens), MSC 38941 (5 specimens) .

Description

Median teeth wider than long, thick-crowned, six-sided with sharp lateral angles. Labial face weakly concave, slightly lingually inclined, has sharp and labially protruding crown foot. Lingual face weakly convex, slightly lingually inclined, has narrow and angular furrow located immediately above a rounded transverse ridge at crown foot. Labial face bears large and widely spaced vertical ridges that become weaker apically. Secondary ornament of fine anastomosing vertical ridges between large ones. Lingual face similarly ornamented, but more strongly than the labial face. The root is polyaulocorhize, labial face basiolingually directed, lingual margin extends beyond the crown foot. Lateral teeth six-sided and may be symmetrical (1:1 width/length ratio) or wider than long (2:1 ratio). Ornament and root morphology consistent with that observed on median teeth.

Remarks

Teeth of Myliobatis sp. 1 occur within the Tallahatta Formation along with several other members of the Myliobatinae , including Pseudaetobatus , Aetomylaeus , and Leidybatis . Myliobatis sp. 1 teeth have inclined, concave/convex labial and lingual faces, as opposed to being vertical and straight on Pseudaetobatus , and the labial and lingual ridging is coarser than on Pseudaetobatus . The occlusal surface of Myliobatis sp. 1 lacks the tuberculated enameloid covering of Leidybatis . Aetomylaeus differs in having a reticulated and tuberculated appearance on the labial and lingual faces, as opposed to being wrinkled. Rhinoptera bears weaker labial and lingual wrinkling, the crown faces are vertical and straight, and the root is very low with a vertical labial face and lingual margin that does not extend past the crown foot. Heavily worn teeth of Myliobatis sp. 1 can be identified by their heavily crenulated labial crown margin. Although similar in gross morphology, Myliobatis sp. 1 differs from the temporally younger Myliobatis sp. 2 of the Lisbon Formation and Gosport Sand (see below) in lacking any reticulation but having a highly crenulated labial crown foot.

Several Eocene species of Myliobatis have been described, but comments on labial/lingual ornament are usually lacking, and dentitions of extant species can be highly variable (see Hovestadt & Hovestadt- Euler 2013). Without having directly compared our Tallahatta teeth to the type specimens of those Eocene species, we cannot confidently make a more specific determination.

Stratigraphic and geographic range in Alabama

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

Figures

Fig. 47. Myliobatis Cuvier, 1816, teeth. A–J. Myliobatis sp. 1. A–E. MSC 38937, median tooth, lower Tallahatta Formation. A. Oral view. B. Basal view. C. Lingual view. D. Labial view. E. Profile view. F–J. MSC 33293, median tooth, lower Tallahatta Formation. F. Oral view. G. Basal view. H. Lingual view. I. Labial view. J. Profile view. — K–T. Myliobatis sp. 2. K–O. MSC 38640, median tooth, Gosport Sand. K. Oral view. L. Basal view. M. Lingual view. N. Labial view. O. Profile view. P–T. MSC 38849.1, lateral tooth, basal Gosport Sand. P. Oral view. Q. Basal view. R. Labial view. S. Lingual view. T. Profile view. Labial at top in oral and basal views. Scale bars: A–O =5 mm; P–T=2 mm.