Anomotodon, Arambourg, 1952

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 : 30-32

Anomotodon sp.

Fig. 10

Material examined

UNITED STATES OF AMERICA – Alabama • 6 isolated teeth; Claiborne Group ; MSC 35766.1 – 2 , MSC 37497, MSC 37503, MSC 37660, MSC 37683 .

Description

Teeth similar in form to those within the Mitsukurinidae and Odontaspididae but lack lateral cusplets. Anterior teeth with tall, slender, erect crown that is sigmoidal in profile view. Lingual crown face strongly convex; labial face flat to slightly convex. Some anterior or anterolateral teeth with short mesial and distal shoulders, but lack cusplets. Crown generally smooth, but faint vertical lingual striations present on some specimens. Anterior teeth narrow, erect, but lateral teeth broader basally, shorter, distally inclined, and labiolingually flattened. Lateral teeth with distinct mesial and distal shoulders, but lack cusplets. Weak striations present at the lingual crown base on some teeth. Root holaulacorhize, bilobate, with thin and rounded lobes and U-shaped interlobe area on anterior teeth. Root lobes of lateral teeth short, strongly divergent, separated by V-shaped interlobe area. Basal face of the root flattened, and nutritive groove present on a prominent lingual root boss.

Remarks

Three Eocene species of Anomotodon are currently recognized, including A. multidenticulatus Long, 1992 , A. novus ( Winkler, 1876), and A. sheppeyensis ( Casier, 1966) (see Cappetta 2012; Carlsen & Cuny 2014). In addition, Case (1994a: 113, pl. 7, figs 141–147, text fig. 6) described and figured teeth he referred to “ Anomotodon sp.”, noting they were more robust than any of the previously described forms. Six teeth within our Claiborne sample have been identified as belonging to Anomotodon , and they can be separated from A. multidenticulatus by the lack of cusplets on the mesial and distal heels. They are not as robust as the unnamed Anomotodon teeth figured by Case (1994a: pl. 7, figs 141–147, text fig. 6). One of the main characteristics used to separate A. novus from A. sheppeyensis is the presence or absence of lingual crown ornamentation (see Casier 1966; Cappetta 1976), which is reportedly absent on the teeth of A. novus ( Cappetta 1976; Carlsen & Cuny 2014). Ornament is present on the anterior and anterolateral teeth of A. sheppeyensis but fades or is absent altogether on the teeth in lateral positions ( Casier 1966; Cappetta 1976).

Of the six teeth in our sample, three have faint plications on their lingual crown face (MSC 37503, MSC 35766.1, MSC 37683; Fig. 10A, G ), and three do not (MSC 35766.2, MSC 37497, and MSC 37660; Fig. 10D ). Furthermore, these specimens were derived from all three formations within the Claiborne Group, with one ornamented and one unornamented tooth from each formation. We cannot, however, ascertain if the same species persisted from the Ypresian (Tallahatta Formation) to the Bartonian (Gosport Sand), or if multiple species are present. In terms of speciation, several interpretations can be drawn:

1. The presence of lingual crown ornamentation on half of our sample suggests they may belong to A. sheppeyensis . Our teeth, however, are smaller and more gracile than the type suite illustrated by Casier (1966: pl. 5, figs 19–25), and fall more within the size range of A. novus (> 1.5 cm in height; see Winkler 1876; Carlsen & Cuny 2014).

2. The small size of these specimens might indicate they represent juvenile teeth of A. sheppyensis . However, the absence of larger, adult, representatives is problematic because of the large sample sizes obtained from the localities from which these specimens were derived.

3. The teeth fall within the size range of A. novus, but the presence of ornamentation is problematical because ornamentation is supposedly absent on the teeth of this taxon. It is possible that A. novus teeth are more variable than previously described, and certain teeth may indeed have lingual ornamentation. Further examination of the type specimen could shed light on this interpretation, as the ornamentation on the specimens in our sample is only visible under magnification.

4. Our teeth could belong to an undescribed, small species of Anomotodon , with ornamented anterior and anterolateral teeth and unornamented laterals. Unfortunately, at this time our sample size is too small (n =6) to substantiate this hypothesis.

Due to our small sample size and the various interpretations of the specimens at hand, we cannot speciate these teeth and assign them to Anomotodon sp.

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 and 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. 10. Anomotodon sp., teeth. A–C. MSC 35766.1, lower Tallahatta Formation. A. Lingual view. B. Labial view. C. Distal view. D–F. MSC 37660, Tallahatta/Lisbon formation contact zone, courtesy of Bruce Relihan. D. Lingual view. E. Labial view. F. Mesial view. G–I. MSC 37503, Gosport Sand. G. Lingual view. H. Labial view. I. Distal view. Scale bars = 5 mm.