Ginglymostoma, Muller & Henle, 1837

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 : 23

Ginglymostoma sp.

Fig. 7 E–H

Material examined

UNITED STATES OF AMERICA – Alabama • 21 isolated teeth; Claiborne Group ; ALMNH PV1993.2.410 (13 specimens), MSC 37522.1 – 4 , MSC 37548.1 – 2 , MSC 37554, MSC 37704 .

Description

Teeth with symmetrical crown and prominent median cusp. Median cusp tall, erect, and triangular, flanked by four pairs of lateral cusplets. Lateral cusplets decrease in size laterally. Distal cusplets are triangular and divergent; mesial cusplets have a slight medial bend. Labial crown face generally flat and smooth; a pair of low ridges is at times present that extends to the crown base. Labial face distally oriented with a shallow basal apron. Basal edge of the apron generally flat or slightly concave. Lingual crown face convex with a strong medial protuberance. Crown T-shaped in oral view. Lateral edges of the root extend beyond the base of the crown. Root base heart-shaped in basal view. Wide nutritive groove on root base that opens labially. Nutritive foramen is positioned within the lingual half of the nutritive groove. Prominent marginolingual foramen present on lingual root protuberance.

Remarks

Unfortunately, only partial and abraded specimens are present in our sample. These teeth ( Fig. 7 E–H) differ from those of Ginglymostoma maroccanum ( Fig. 7 A–D) by having four pairs of lateral cusplets, as opposed to three, and the cusplets are mesiodistally not as wide. Furthermore, the mesial cusplets on these teeth have a slight medial bend, as opposed to the more divergent cusplets on the teeth of G. maroccanum . Due to the poor state of preservation of the teeth in our sample, all are assigned to Ginglymostoma sp. These teeth, however, differ from the other known Paleogene Ginglymostoma species by having a shorter and less triangular median cusp than on G. khourbgaense , they have a much more pronounced labial apron than on G. maghrebianum , wider and shorter cusplets than on G. subafricanum , and a different number of pairs of lateral cusplets than G. angolense (six or more), G. khourbgaense (one to three), and G. serra (five to nine). These teeth are most similar to the Thanetian G. chenanei , which can have up to four pairs of lateral cusplets, however the lateral cusplets and median cusp on the teeth of G. chenanei have much straighter mesial and distal edges than those on the teeth in our sample. Furthermore, the Ginglymostoma sp. specimens in our sample were recovered from the stratigraphically much younger Bartonian Gosport Sand. It is possible the Bartonian teeth in our sample represent a unique taxon, but better-preserved material is needed to corroborate this hypothesis.

Stratigraphic and geographic range in Alabama

Ginglymostoma sp. specimens have been recovered only from the basal Gosport Sand at site ACl-4. Middle Bartonian, Zone NP17.

Figures

Fig. 7. Ginglymostomatidae Gill, 1862, teeth. A–D. Ginglymostoma maroccanum Noubhani & Cappetta, 1997, MSC 34407.2, lower Tallahatta Formation. A. Labial view. B. Lingual view. C. Mesial view. D. Basal view. — E–H. Ginglymostoma sp., MSC 37548.1, basal Gosport Sand. E. Labial view. F. Lingual view. G. Mesial view. H. Basal view. — I–T. Nebrius thielensi (Winkler, 1874). I–L. MSC 35755.6, lower Tallahatta Formation. I. Labial view. J. Lingual view. K. Mesial view. L. Basal view. M–P. MSC 37266.1, basal Lisbon Formation. M. Labial view. N. Lingual view. O. Distal view. P. Basal view. Q–T. MSC 37496.1, basal Gosport Sand. Q. Labial view. R. Lingual view. S. Profile view. T. Basal view. Labial at bottom in basal views. Scale bars = 3 mm.