Rhinobatos ” bruxelliensis ( Jaekel, 1894 )

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 : 106-108

“ Rhinobatos ” bruxelliensis ( Jaekel, 1894)

Fig. 38

Rhinobatus bruxelliensis Jaekel, 1894: 77 , fig. 8.

Rhinobatos bruxelliensis – Cappetta 1976: 564 , pl. 4, fig. 7.

Rhinobatos sp. – Holman & Case 1988: 328.

Rhinobatis sp. – Feldmann & Portell 2007: 90.

“ Pristidae oral teeth?” – Cappetta & Case 2016: 62, pl. 10, figs 5–8.

Material examined

UNITED STATES OF AMERICA – Alabama • 68 isolated teeth; Claiborne Group ; ALMNH PV1993.7.490 (5 specimens), MSC 35787.1 – 3 , MSC 37315.1 – 2 , MSC 37550.1 – 9 , MSC 37670.1 – 2 , MSC 37689.1 – 8 , MSC 37902, MSC 37903.1 – 2 , MSC 37903.2 , SC 2012.47.1, SC 2012.47.2, SC 2012.47.3 (20 specimens), WSU 10 , WSU CC 445 , WSU CC 505 (2 specimens), WSU 5049 (10 specimens) .

Description

Teeth extremely small, most not exceeding 2 mm in mesiodistal width. Crown has weakly convex, smooth labial face with broadly convex crown foot. Lingual face bearing three uvulae, separated by a transverse crest of varying lengths. Medial lingual uvula is most prominent; being narrow and elongated towards the succeeding tooth. Lateral uvulae are much shorter and divergent. Uvulae extend onto upper surface of root and have rounded extremities. Faint longitudinal ridge may be present on medial uvula. Most teeth lack cusps; some have taller, more cuspidate crown (see Fig. 38 Q–T). Root positioned lingually under the crown. Root T-shaped in basal view. Lateral root extremities project below the lateral crown uvulae. Prominent nutritive groove extends labiolingually across the root base. Nutritive foramen present within nutritive groove; additional foramina often visible on lingual root face.

Remarks

The Rhinobatos teeth in our sample are conspecific with those of Rhinobatos bruxelliensis ( Jaekel, 1894) in that the lateral uvulae are divergent, with the medial uvula being more pronounced than the lateral ones, and the uvulae all have rounded extremities. The teeth also have a characteristic apical transverse ridge that separates the crown into labial and lingual faces. Holman & Case (1988) and Feldmann & Portell (2007) each reported specimens they assigned to Rhinobatos sp. from the contact of the Tallahatta and Lisbon formations at site ACov-11. Although these specimens were not examined as part of this study, our sample included numerous Rhinobatos specimens collected from the same locality, all of which fall within the morphological range of R. bruxelliensis . This suggests the Holman & Case (1988) and Feldmann & Portell (2007) specimens also belong to this taxon.

Cappetta & Case (2016) figured four specimens (pl. 10, 5–8) from the ACov-11 locality that have the R. bruxelliensis morphology. These authors, however, questioned the identification of the teeth as Rhinobatos , suggesting instead they belong to a member of the Pristidae Bonaparte, 1838 . Although teeth of these two taxa are similar, Cappetta & Case (2016) appear to argue for a pristid identification simply because their sample included numerous Pristis Linck, 1790 rostral spines, but otherwise lacked Pristis oral teeth. This interpretation seems problematic, as teeth of very similar morphology, identified as Rhinobatos , have been reported from Cretaceous strata, a time well before the first occurrence of the Pristidae in the Paleogene (see Cappetta 2012). Furthermore, Pristis teeth have a very elongated medial lingual uvula but lack lateral uvulae ( Carrillo-Briceño et al. 2015, 2016), which is inconsistent with the teeth in our sample.

We do concur that the teeth of the bruxelliensis morphology are dissimilar to those of the extant Rhinobatos , and the tooth morphology of living and fossil rhinobatid species should be reviewed. Recent phylogenetic studies have shown Rhinobatos to be paraphyletic (see Naylor et al. 2012; Claeson et al. 2013), calling into question the placement of fossil and living species within this genus, and casting doubt that they can all be placed into the family Rhinobatidae . Thus, we provisionally assign the bruxelliensis teeth in our sample to “ Rhinobatos ” and place them tentatively within the Rhinobatidae .

Stratigraphic and geographic range in Alabama

The specimens in our sample were collected from the lower Tallahatta Formation at site ADl-1, the basal Lisbon Formation at site ACov-11, the “upper” Lisbon Formation at site ACh-8, and the basal Gosport Sand at site ACl-4. Upper Ypresian to middle Bartonian, zones NP14 to NP17.

Family Pristidae Bonaparte, 1838

Figures

Fig. 38.“Rhinobatos” bruxelliensis(Jaekel, 1894), teeth.A–D. MSC 35787.1, lowerTallahatta Formation. A. Orolingual view. B. Profile view. C. Basal view. D. Labial view. E–H. MSC 35787.2, lower Tallahatta Formation. E. Orolingual view. F. Profile view. G. Basal view. H. Labial view. I–L. MSC 37315.1, basal Lisbon Formation. I. Orolingual view. J. Profile view. K. Basal view. L. Labial view. M–P. MSC 37315.2, basal Lisbon Formation. M. Orolingual view. N. Profile view. O. Basal view. P. Labial view. Q–T. MSC 37550.1, male tooth, basal Gosport Sand. Q. Orolingual view. R. Profile view. S. Basal view. T. Labial view. U–X. MSC 37550.2, basal Gosport Sand. U. Orolingual view. V. Profile view. W. Basal view. X. Labial view. Labial at top in basal views. Scale bars = 1 mm.