Hypotodus verticalis (Agassiz, 1843)

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 : 45-47

Hypotodus verticalis (Agassiz, 1843)

Fig. 15

Lamna hopei Agassiz, 1843: 293 , pl. 37a, figs 28, 30.

Lamna verticalis Agassiz, 1843: 294 , pl. 37a, fig. 31.

Otodus vincenti Winkler, 1874a: 11 , figs 9–10.

Odontaspis hopei affinia Casier, 1946: 64 , pl. 2, fig. 9.

Odontaspis verticalis – Casier 1946: 70 , pl. 2, fig. 13.

Synodontaspis hopei – Nolf 1988 : pl. 25, fig. 8.

Hypotodus verticalis – Nolf 1988 : pl. 29, figs 3–7. — Cappetta & Nolf 2005: 244, pl. 4.

Carcharias hopei – Ward 1988: 1 , pl. 2, figs 1–17, pl. 6, text-fig. 2.

Eugomphodus verticalis – Kruckow & Thies 1990: 36 .

Material examined

UNITED STATES OF AMERICA – Alabama • 121 isolated teeth; Claiborne Group ; ALMNH PV1992.28.18c, ALMNH PV2016.4.57b, MMNS VP-8954 (37 specimens), MSC 2372.3 , MSC 33265, MSC 33305, MSC 33315, MSC 33360, MSC 33367, MSC 33368, MSC 33377, MSC 33399, MSC 33408, MSC 33464, MSC 33467, MSC 33499, MSC 33516, MSC 33543, MSC 33552, MSC 33553, MSC 33558, MSC 33563, MSC 33583, MSC 33586, MSC 33877, MSC 33897, MSC 33899, MSC 33933, MSC 35784.1 – 3 , MSC 36177, MSC 37013, MSC 37014, MSC 37054.1 – 6 , MSC 37055.1 – 3 , MSC 37060.1 – 4 , MSC 37062.1 – 3 , MSC 37063, MSC 37103.1 – 3 , MSC 37114.1 – 5 , MSC 37131, MSC 37143.1 – 5 , MSC 37159, MSC 37295, MSC 37296, MSC 37313, MSC 37535, MSC 38473.1 – 2 , MSC 39012, NJSM 24020 (2 specimens), SC 2012.47.162, SC 2012.47.76, SC 2012.47.77 (2 specimens), SC 2012.47.90 (5 specimens), WSU 5003 .

Description

All teeth with single pair of lateral cusplets that angle medially. Crown faces smooth. Labial crown face flat; lingual face convex. Cutting edges incomplete and never reach the lateral cusplets. Root bilobed with rounded root lobes. Prominent nutritive groove present on lingual root protuberance. Upper anterior teeth with long, slender, and triangular main cusp with a slight distal inclination. Root lobes divergent and elongated mesially. Base of the main cusp wider in upper anterior files. Cusplets more needle-like in anterior files. Apex on upper lateral teeth generally have a slight labial bend. Lower anterior teeth with taller and labiolingually thinner main cusp than on upper anterior files. Root protuberance more pronounced on lower anterior teeth and have a more sigmoidal cusp. Main cusp on upper lateral teeth short and triangular with distinctive distal hook. Base of the main cusp on upper lateral teeth are wider than other tooth positions, the cusplets more triangular, and lingual boss reduced. Root lobes on upper lateral teeth labiolingually compressed. Interlobe area on upper lateral teeth V-shaped; U-shaped on all other files. Main cusp on lower anterolateral teeth more triangular than other files. Main cusp on lower anterolateral teeth more erect and slenderer than on upper anteriors. Main cusp on lower anterolateral teeth with slight distal bend and root with elongated mesial lobe.

Remarks

Agassiz (1843) originally named Lamna hopei and Lamna verticalis , two taxa that were subsequently placed by Cappetta (1987) within the genus Hypotodus Jaekel, 1895 . Ward (1988) later questioned the validity of Hypotodus and placed L. hopei in the genus Carcharias . He also argued that H. verticalis and C. hopei were conspecific, ultimately designating H. verticalis a junior synonym of C. hopei . Cappetta (1987) and Cappetta & Nolf (2005) later argued that H. verticalis was indeed a valid taxon because, as they determined, the presence of two upper anterior teeth separated the species from all the known members of the Odontaspididae and thus warranted placement within its own genus. Currently Hypotodus is monospecific and is only represented by the type species, H. verticalis . We follow Cappetta & Nolf (2005) in recognizing the validity of H. verticalis because all specimens in our sample have incomplete cutting edges that terminate well short of the lateral cusplets. This unique characteristic separates the teeth of this taxon from similar genera in our sample like Brachycarcharias and Jaekelotodus , both of which have complete cutting edges that extend to the base of the main cusp. Anterior teeth of Striatolamia also have incomplete cutting edges, but the presence of longitudinal ridges on the lingual cusp face contrasts with the smooth faces of Hypotodus teeth. In addition, Striatolamia lateral teeth attain larger sizes, are broader and bear lingual ornamentation, and the cusplets are broader and more closely connected to the main cusp. Hypotodus lateral teeth differ from those of Brachycarcharias in having a single pair of comparatively smaller lateral cusplets, and from Jaekelotodus by having a less hooked main cusp and broader lateral cusplets.

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, the contact of the Tallahatta and Lisbon formations at sites ACh-14 and ACov-11, the basal Lisbon Formation at site ACov-11, “upper” Lisbon Formation at site ACl-3, and the basal Gosport Sand at site ACl-4, and the Gosport Sand at site ACh-21. Upper Ypresian to middle Bartonian, zones NP12 to NP17.

Figures

Fig. 15. Hypotodus verticalis (Agassiz, 1843), teeth. A–C. MSC 37055.1, anterior tooth, Meridian Sand Member of the Tallahatta Formation. A. Labial view. B. Lingual view. C. Mesial view. D–F. MSC 33908, anterior tooth, lower Tallahatta Formation. D. Labial view. E. Lingual view. F. Distal view. G–I. MSC 37296, lateral tooth, basal Lisbon Formation. G. Labial view. H. Lingual view. I. Mesial view. J–L. MSC 36177, upper lateral tooth, Tallahatta/Lisbon formation contact zone, courtesy of James Lowery. J. Labial view. K. Lingual view. L. Mesial view. M–O. MSC 37103.1, anterior tooth, Tallahatta/Lisbon formation contact zone, courtesy of Bruce Relihan. M. Labial view. N. Lingual view. O. Distal view. P–R. MSC 37159, anterior tooth, Tallahatta/Lisbon contact zone, courtesy of James Lowery. P. Labial view. Q. Lingual view. R. Mesial view. Scale bars = 1 cm.