Abdounia minutissima (Winkler, 1874)

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 : 86-87

Abdounia minutissima (Winkler, 1874)

Fig. 31 P–GG

Otodus minutissimus Winkler, 1874a: 23 .

Scyllium minutissimus – Daimeries 1891: 73 .

Scyllium minutissimum – Leriche 1905: 186 , pl. 5, fig. 15.

Scyliorhinus minutissumus – White 1931: 65 , fig. 80.

Abdounia minutissima – Cappetta 1980a: 37 .

Abdounia minutissimus – Baut & Genault 1995: 226 .

Scyliorhinus sp. – Maisch et al. 2014: 192, fig. 3, 17–19.

Material examined

UNITED STATES OF AMERICA – Alabama • 71 isolated teeth; Claiborne Group ; GSA-V706, MMNS VP-8192 (3 specimens), MSC 35757.1 – 2 , MSC 35768.1 – 5 , MSC 37573, MSC 37574.1 – 2 , MSC 37575.1 – 16 , MSC 37576.1 – 3 , MSC 37577.1 – 12 , MSC 37694, MSC 37707, MSC 37900.1 – 5 , SC 2012.47.49, SC 2012.47.50 (9 specimens), SC 2012.47.158, WSU 5014 , WSU 5015 , WSU 5032 (6 specimens) .

Description

Teeth small, most not exceeding 4.0 mm high. Main cusp of anterior teeth tall and triangular; cusp wider, lower, distally inclined on lateral teeth. Cusp flanked by single pair of tall triangular lateral cusplets in all tooth positions. Base of lateral cusplets separated from main cusp; cusplets slender, tall, erect. Cutting edges of main cusp and cusplets smooth, continuous. Lingual crown face convex, less so on lateral teeth; labial crown face flat; enameloid smooth. Root bilobate with short, diverging lobes. Lingual attachment surface flat, bisected by deep nutritive groove.

Remarks

The A. minutissima anterior teeth in our sample have a single pair of lateral cusplets in all tooth positions, whereas two species formerly placed within Abdounia (see below), A. claibornensis and A. recticona , have three-to-eight pairs. The anterior teeth of A. minutissima were distinguished from those of A. beaugei by having lateral cusplets that are taller, more slender, and more conspicuously differentiated from the main cusp. The teeth of A. minutissima differ from those of A. enniskilleni by their smaller size and more gracile appearance, by having a smooth lingual crown face, and by having narrower lateral cusplets.

Cappetta & Case (2016) referred 120 teeth from the contact of the Tallahatta and Lisbon Formation at site ACov-11 to Abdounia sp. and questioned the assignment of teeth to A. minutissima by Clayton et al. (2013). Cappetta & Case (2016) stated that the 120 teeth were similar to those of A. minutissima , but noted that they lack short folds at the base of the labial crown face and have a thicker root. However, the type specimens of A. minutissima originally illustrated by Winkler (1874a) lack any labial folds, and the presence of such ornamentation was not mentioned by either Winkler (1874a) or later by Daimeries (1891). The presence of faint labial ornamentation on the teeth of A. minutissima was first reported by Leriche (1905), but he noted that these vertical striations are extremely faint, almost invisible to the naked eye, and were extremely susceptible to abrasion. This lack of ornamentation on certain teeth is substantiated by its absence on several figured A. minutissima specimens by other authors, at least one of which was derived from the type locality in Belgium (see Van den Eeckhaut & De Schutter 2009: pl. 20, fig. 6). Furthermore, an examination of the A. minutissima teeth in our sample suggests that the thickness of the root is variable and can be attributed to heterodonty. Additionally, the presence or absence of labial ornamentation, as well as root thickness and cusplet morphology, is variable in large samples of A. enniskilleni teeth from both Alabama and South Carolina that we examined. The taxonomic utility of crown ornamentation may not be significant ( Purdy et al. 2001), as it is also variable within the various species of Premontreia that have been identified ( Cappetta 1992; Noubhani & Cappetta 1997).

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the lower Tallahatta Formation at site ADl-1, the Tallahatta Formation at AMo-8, the contact of the Tallahatta and Lisbon formations and the basal Lisbon Formation at site ACov-11, the contact of the Lisbon Formation and Gosport Sand at site AMo- 4, the basal Gosport Sand at site ACl-4, and the Gosport Sand at site ACl-15. Upper Ypresian to middle Bartonian, zones NP14 to NP17.

Figures

Fig. 31. Abdounia enniskilleni (White, 1956) and A. minutissima (Winkler, 1874), teeth. A–O. A. enniskilleni. A–C. MSC 2171.8, anterior tooth, basal Gosport Sand. A. Labial view. B. Lingual view. C. Mesial view. D–F. MSC 37620, anterior tooth, “upper” Lisbon Formation, courtesy of James Lowery. D. Labial view. E. Lingual view. F. Mesial view. G–I. MSC 37567.1, anterior tooth, basal Gosport Sand. G. Labial view. H. Lingual view. I. Mesial view. J–L. MSC 1424.2, lateral tooth, basal Gosport Sand. J. Labial view. K. Lingual view. L. Mesial view. M–O. MSC 188.292, lateral tooth, basal Gosport Sand. M. Labial view. N. Lingual view. O. Mesial view. — P–GG. A. minutissima. P–R. MSC 35768.2, lateral tooth, lower Tallahatta Formation. P. Labial view. Q. Lingual view. R. Mesial view. S–U. MSC 35768.1, anterior tooth, lower Tallahatta Formation. S. Labial view. T. Lingual view. U. Distal view. V–X. MSC 37574.1, lateral tooth, basal Gosport Sand. V. Labial view. W. Lingual view. X. Mesial view. Y–AA. MSC 37574.2, anterior tooth, basal Gosport Sand. Y. Labial view. Z. Lingual view. AA. Distal view. BB–DD. MSC 37577.1, anterior tooth, basal Lisbon Formation. BB. Labial view. CC. Lingual view. DD. Mesial view. EE–GG. MSC 37577.2, anterior tooth, basal Lisbon Formation. EE. Labial view. FF. Lingual view. GG. Mesial view. Scale bars: A–O=5 mm; P–GG =2 mm.