Tethylamna dunni Cappetta & Case, 2016

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 : 53-56

Tethylamna dunni Cappetta & Case, 2016

Fig. 19

Tethylamna dunni Cappetta & Case, 2016: 51 , pl. 5, fig. 21.

Material examined

UNITED STATES OF AMERICA – Alabama • 96 isolated teeth; Claiborne Group ; ALMNH PV1989.4.126a, ALMNH PV1989.4.175a, ALMNH PV1989.4.177a, ALMNH PV1989.4.204, ALMNH PV1989.4.208a, ALMNH PV1992.28.16 (5 specimens), ALMNH PV1992.28.23, ALMNH PV1992.28.28 (3 specimens), ALMNH PV2000.1.43.1a (3 specimens), ALMNH PV2016.3.262c (2 specimens), ALMNH PV2016.3.264, ALMNH PV2016.3.264, ALMNH PV2016.4.57a, ANSP 23409 , MMNS VP-8950 (6 specimens), MMNS VP-8955 (16 specimens), MSC 34624.4 , MSC 37072, MSC 37073.1 – 2 , MSC 37074.1 – 2 , MSC 37075.1 – 3 , MSC 37076.1 – 6 , MSC 37077.1 , MSC 37077.3 – 4 , MSC 37077.7 – 8 , MSC 37078.1 – 7 , MSC 37112, MSC 37259.1 – 7 , MSC 37294.1 – 5 , MSC 37479, MSC 37585.1 , MSC 38526, MSC 38626, SC 2012.47.250 (3 specimens), WSU CC 536 (2 specimens), WSU CC 537.1 , WSU CC 543 .

Description

Anterior teeth with erect triangular, broad-based main cusp. Main cusp bi-convex, with smooth, continuous cutting edges extending from apex to base of crown and across lateral cusplets. Lingual crown face strongly convex, smooth; labial face flat to slightly convex, smooth. Single pair of relatively large, sharply pointed, medially curving cusplets. Anterolateral teeth with less symmetrical main cusp, and cusplets becoming wider and often two pairs developed. Root bilobate, with elongate, rounded, diverging lobes separated by V-shaped interlobe area; deep nutritive groove present on pronounced lingual root boss. Lateral teeth with broadly triangular, distally inclined main cusp that is labiolingually thinner than anterior teeth. Continuous cutting edges along main cusp, extending to main cusp base and across lateral cusplets; mesial edge straight to convex, whereas distal edge straight to slightly concave. Lingual crown face moderately convex, smooth; labial face flat with faint vertical wrinkling at crown base on some specimens. Two pairs of lateral cusplets generally present, with a third vestigial distal cusplet occasionally observed. All cusplets distally inclined, with first pair always larger than second pair, and first distal cusplet usually conspicuously larger than the mesial one. Mesial edge of largest cusplets usually convex, distal edge straight. Base of cusplets on some teeth are positioned labial to the cutting edge of the main cusp. Root lobes short, angular, strongly divergent, separated by shallow V-shaped interlobe area. Conspicuous nutritive groove on lingual root boss.

Remarks

This species was first described by Cappetta & Case (2016) based on specimens derived from the contact of the Tallahatta and Lisbon formations at site ACov- 11 in Covington County, AL. These authors noted their provisional placement of the genus within the Odontaspididae . Cappetta & Case (2016: pl. 5: 1–2) figured two specimens that they identified as parasymphyseal teeth, but it is unclear to us as to why they arrived at that conclusion. If these teeth are from the lower dentition, we cannot know if they occurred on the side of the jaw symphysis, adjacent to the first anterior tooth, or if they occurred within the first dental hollow along with the anterior teeth. If the latter case, we believe the “parasymphyseal” teeth would more appropriately be identified as the first anterior position.

Anterior teeth of Tethylamna dunni are distinguished from those of Hypotodus in having a more robust main cusp with complete cutting edges.Lateral teeth of Tethylamna differ from those of Brachycarcharias , Hypotodus , and Jaekelotodus in having larger lateral cusplets that are mesially directed, and the distal cusplet is usually larger than the mesial one. Anterior teeth of Striatolamia are much narrower than those of Tethylamna, with diminutive lateral cusplets, incomplete cutting edges, and strong lingual ornamentation. The lateral teeth differ from Tethylamna in having a single pair of lateral cusplets and faint lingual ornamentation.

One curious specimen in our sample, MSC 34624.4 ( Fig. 19 Z–AA), is here tentatively assigned to Tethylamna sp. Although this specimen appears to have affinities with T. dunni , it differs by being nearly 1.5 cm taller and wider than any of the T. dunni specimens we observed. This specimen also differs by having a wider crown base, and mesial and distal cusplets that are positioned labially to the main cusp. Although this characteristic has been observed on some of the T. dunni teeth in our sample, it generally occurs only on one side, and to a lesser degree, allowing the mesial and distal cutting edge to extend continuously across the lateral cusplets. Due to the labial position of the cusplets on MSC 34624.4, the cutting edge is not continuous across the lateral cusplets. Moreover, although two pairs of lateral cusplets are present on this specimen, the outer pair is greatly reduced compared to those on T. dunni , and almost appear vestigial. The more medial, larger, pair of cusplets are also curious as they are lanceolate in shape and have a strong lingual bend. On the teeth of T. dunni , the anterolateral and lateral teeth have cusplets that are similar in shape, but they are erect and not lingually bent. Although the cusplets on the anterior teeth of T. dunni are often lingually directed (as well as medially), they are cylindrical and not lanceolate such as those on MSC 34624.4. Although the slight morphological differences might suggest MSC 34624.4 represents a distinct species, we refrain from such a distinction as our sample consists of a single isolated tooth. Although we provisionally assign this tooth to Tethylamna sp., the collection of additional specimens might show MSC 34624.4 to be taxonomically distinct.

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the lower Tallahatta Formation at site AD 1-1, the contact of the Tallahatta and Lisbon Formations at sites ACov-11 and ACon-6, the basal Lisbon Formation at site ACov-11, the “upper” Lisbon Formation at site ACl-3, the “upper” Lisbon Formation and basal Gosport Sand at site ACl-4, and the Gosport Sand at site ACh-21. Upper Ypresian to middle Bartonian, zones NP14 to NP17.

Family Lamnidae Müller & Henle, 1838

Figures

Fig. 19 (opposite page). Tethylamna Cappetta & Case, 2016, teeth. A–X. T. dunni Cappetta & Case, 2016. A–C. MSC 37077.1, anterior tooth, Tallahatta/Lisbon formation contact zone, courtesy of Bruce Relihan. A. Labial view. B. Lingual view. C. Mesial view. D–F. MSC 37077.4, anterior tooth, Tallahatta/Lisbon formation contact zone, courtesy of Bruce Relihan. D. Labial view. E. Lingual view. F. Mesial view. G–I. MSC 37077.8, lateral tooth, Tallahatta/Lisbon formation contact zone, courtesy of Bruce Relihan. G. Labial view. H. Lingual view. I. Mesial view. J–L. MSC 37078.6, lateral tooth, Tallahatta/Lisbon formation contact zone, courtesy of James Lowery. J. Labial view. K. Lingual view. L. Mesial view. M–O. MSC 37077.7, lateral tooth, Tallahatta/Lisbon formation contact zone, courtesy of Bruce Relihan. M. Labial view. N. Lingual view. O. Mesial view. P–R. MSC 37585.1, lateral tooth, “upper” Lisbon Formation. P. Labial view. Q. Lingual view. R. Mesial view. S–U. MSC 37078.4, lateral tooth, Tallahatta/Lisbon formation contact zone, courtesy of James Lowery. S. Labial view. T. Lingual view. U. Mesial view. V–X. MSC 37078.5, lateral tooth, Tallahatta/Lisbon formation contact zone, courtesy of James Lowery. V. Labial view. W. Lingual view. X. Mesial view. — Y–AA. Tethylamna aff. T. dunni, MSC 34624.4, anterolateral tooth, “upper” Lisbon Formation. Y. Labial view. Z. Lingual view. AA. Mesial view. Scale bars = 1 cm.