Egertonia isodonta Cocchi, 1864

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 : 156-157

Egertonia isodonta Cocchi, 1864

Fig. 58

Egertonia isodonta Cocchi, 1864: 121 , pl. 4, figs 1–2.

Triodon sp. – Case 1981: pl. 2, fig. 21.

Material examined

UNITED STATES OF AMERICA – Alabama • 128 isolated teeth; Claiborne Group ; ALMNH PV1992.28.2, ALMNH PV1993.2.0458 (23 specimens), ALMNH PV2016.4.39, MMNS VP-5646 (3 specimens), MMNS VP-5647, MMNS VP-8227, MSC 33348, MSC 35780.1 – 34 , MSC 37125, MSC 37157, MSC 37323, MSC 37505.1 – 37 , MSC 37651, MSC 37913.1 , MSC 38496.1 – 12 , MSC 38562, MSC 38971, NJSM 24040 , NJSM 34316 , SC 2012.47.126 (3 specimens), SC 2012.47.127 (2 specimens) .

Description

Isolated teeth very low, flat to weakly convex, with circular to sub-hexagonal occlusal outline. A thin concentric ring is present at the tooth base on some specimens. Teeth largely consist of smooth enameloid crowns, with large open basal pulp cavity. Pulp cavity flat to weakly concave. Tooth plates with sub-oval occlusal outline, flat to dome-shaped in profile, consisting of vertically stacked rows of teeth. Largest teeth positioned medially within tooth plate; tooth diameter decreases laterally. Tooth stacking very tight, little interstitial bone.

Remarks

Isolated Egertonia teeth could be confused with the sub-circular, peripheral teeth of Phyllodus , but they differ by lacking ornamentation and by the presence of a thickened band at the base of most teeth. Although variable, Egertonia teeth can also be slightly more dome-shaped than those of Phyllodus . Egertonia basibrachial tooth plates are morphologically similar to those of Phyllodus in that they consist of regular stacks of teeth. However, Egertonia tooth plates differ by lacking a medial row of sub-ovate teeth as occurs on the tooth plates of Phyllodus . Egertonia tooth plates differ from those of Paralbula by having unornamented teeth with a lower profile, and by having regular stacks of teeth, as opposed to irregularly overlapping teeth.

Egertonia is currently a monospecific genus, and the isolated teeth and tooth plates in our sample all appear conspecific with the only known species, Egertonia isodonta , as described and figured by Cocchi (1864), Casier (1966), Estes (1969), and Weems (1999).

Maisch et al. (2016: pl. 2, figs 7–8) described and figured a partial tooth plate (NJSM 24316) that they assigned to Paralbula marylandica . Our reexamination of this specimen showed that it instead belongs Egertonia isodonta , as individual teeth have an evenly convex crown, lack a pulp cavity, and the teeth are evenly stacked in vertical rows in profile view.

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from 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, 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. 58. Egertonia isodonta Cocchi, 1864. A–C. MSC 33348, tooth plate, lower Tallahatta Formation. A. Oral view. B. Profile view. C. Aboral view. D–F. MSC 37651, stack of teeth, Tallahatta/Lisbon formation contact zone, courtesy of Bruce Relihan. D. Oral view. E. Lateral view. F. Aboral view. G–I. MSC 37913.1, tooth, basal Lisbon Formation. G. Oral view. H. Lateral view. I. Aboral view. J–L. MSC 37555.1, stack of teeth, basal Gosport Sand. J. Oral view. K. Lateral view. L. Aboral view. M–O. MSC 35780.1, tooth, lower Tallahatta Formation. M. Oral view. N. Lateral view. O. Aboral view. Scale bar for A–C =1 cm. Scale bars for D–O =2 mm.