Mennerotodus, Zhelezko, 1994

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 : 50-52

Mennerotodus sp.

Fig. 17

Material examined

UNITED STATES OF AMERICA – Alabama • 5 isolated teeth; Claiborne Group; ALMNH PV1989.4.16.1.1, ALMNH PV1989.4.17.3.8, ALMNH PV1989.4.20.1, ALMNH PV1989.4.34.1, ALMNH PV1989.4.203.1.

Description

Both anterior and upper lateral teeth present in our sample. Anterior teeth with tall, triangular main cusp with smooth labial and lingual faces. Labial crown face slightly convex; lingual face strongly convex. Main cusp only slightly sigmoidal in profile view. Single pair of short, triangular lateral cusplets present at base of main cusp, with tiny rounded denticulation at the base of the mesial side of the main cusp, just before the first cusplet. Lateral cusplets appear well separated from the main cusp in lingual view. Deep medial depression occurs at base of labial crown face. Root lobes elongate, basally tapering, slightly diverging, sub-rounded. Deep U-shaped interlobe area. Very pronounced lingual protuberance; boxlike in basal view, with shallow but wide nutritive groove. Lateral teeth have a shorter, broad-based but apically narrow main cusp that may be erect or distally inclined. Labial face of main cusp flat to slightly convex; lingual face very convex. Crown labially inclined in profile view. Mesial and distal cutting edges do not extend to the lateral cusplets. One-to-two pairs of divergent lateral cusplets present. Secondary pairs of cusplets are smaller and always positioned lateral to the larger, medial pair. Cusplets tend to have a slight medial bend. One or more minute, triangular, denticulations present between the medial pair of cusplets and cutting edges. Up to two denticulations may be present mesially, with no more than one present distally, if present at all. Root lobes triangular with rounded ends, strongly divergent. Interlobe area shallow, V-shaped. Lingual root protuberance inconspicuous but has deep nutritive groove.

Remarks

The five specimens in our sample are morphologically very similar those of the Recent Carcharias taurus Rafinesque, 1810 , and we used dentitions of this extant taxon to determine hypothetical tooth positions for the Mennerotodus teeth in our sample. Mennerotodus teeth differ from C. taurus , and all the other Claiborne odontasipids in our sample, by the conspicuous presence of distinct denticulations located between the lateral cusplets and mesial cutting edge on the teeth (these denticulations may be present on the distal edge as well but are more prevalent mesially). This feature is not present on teeth within any of the C. taurus jaw sets examined at SC and USNM (n=5) but has been reported on a small number of Jaekelotodus trigonalis ( Jaekel, 1895) teeth (see Cappetta & Nolf 2005; Van den Eeckhaut & De Schutter 2009). The teeth in our sample, however, are smaller, more gracile, and have a mesiodistally thinner main cusp than those of J. trigonalis and are more consistent with the morphology of the middle Eocene Mennerotodus glueckmani as described and illustrated by Zhelezko (1994). The specimens in our sample appear to differ from those of the type species, M. glueckmani , by having a shorter and more robust main cusp, but a larger sample is needed to make more direct comparisons to previously described species. A more detailed study of the occurrences of this genus in North America is currently being undertaken by the present authors.

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the Gosport Sand at site ACh-21. Middle Bartonian, Zone NP17.

Figures

Fig. 17. Mennerotodus sp., teeth. A–E. ALMNH PV1994.4.16.1, upper right lateral tooth, Gosport Sand. A. Close-up of mesial denticulations. B. Labial view. C. Lingual view. D. Mesial view. E. Basal view. F–J. ALMNH PV1994.4.203.1, upper right lateral tooth, Gosport Sand. F. Close-up of mesial denticulation. G. Labial view. H. Lingual view. I. Mesial view. J. Basal view. K–O. ALMNH PV1989.4.17.3.8, upper left lateral tooth (reversed for comparison), Gosport Sand. K. Close-up of mesial denticulation. L. Labial view. M. Lingual view. N. Mesial view. O. Basal view. P–T. ALMNH PV1989.4.20, lower left second anterior tooth, Gosport Sand. P. Close-up of mesial denticulation. Q. Labial view. R. Lingual view. S. Mesial view. T. Basal view. Labial at bottom in basal views. Scale bars = 1 cm.