Rhinobatos undetermined

Cicimurri, David J. & Knight, James L., 2019, Late Eocene (Priabonian) elasmobranchs from the Dry Branch Formation (Barnwell Group) of Aiken County, South Carolina, USA, PaleoBios 36, pp. 1-31 : 16-17

RHINOBATOS SP.

( FIG. 6A–D )

Referred specimen —SC2013.38.45, tooth.

Remarks —The single tooth can be distinguished from teeth of Rhynchobatus Müller and Henle, 1837 (see below) in lacking crown ornamentation, the medial lingual protuberance is very narrow, and flanking lateral protuberances are present ( Fig. 6A ). The crown apex is worn, and it is unclear if this tooth was low-crowned (female) or cuspidate (male). The tooth is identical to Rhinobatos teeth from the temporally older Clinchfield Formation of central Georgia (DJC, unpublished data). Although represented by a single specimen, the Dry Branch Rhinobatos exhibits features in common with middle to late Eocene Rhinob. steurbauti Cappetta and Nolf, 1981 , including an elongated central lingual protuberance flanked by much smaller and slightly diverging lateral protuberances ( Cappetta and Nolf 1981, Case et al. 1996). Rhinobatos teeth occurring in upper Eocene strata of Georgia and Louisiana appear to be conspecific with the Dry Branch Formation species, and we believe that those records were erroneously identified as the Cretaceous taxon Rhinob. casieri Cappetta and Case, 1975 ( Case 1981, Manning and Standhardt 1986). Manning and Standhardt (1986) used the presence of Rhinobatos in a paleofauna as an indicator of a middle shelf-depth environment.

Cappetta and Case (2016) recently identified similar teeth from middle Eocene strata of Alabama as Pristis Linck, 1790 . However, those teeth clearly have an elongat- ed medial uvula flanked by lateral uvulae, whereas Pristis teeth lack lateral uvulae ( Carrillo-Briceño et al. 2015, Carrillo-Briceño et al. 2016). Negative evidence within the Dry Branch Formation sample, which lacks Pristidae Bonaparte, 1838 rostral spines, indicates sawfish were not present at the time of deposition. For the purposes of this report we identify SC2013.38.45 as Rhinobatos , but our generic assignment could change with a larger sample size that will allow for better comparisons to the tooth morphologies of other extant rhinopristiform genera. The Dry Branch Formation tooth bears some similarity to Glaucostegus typus Bennett, 1830 (Underwood et al. 2015), but its labial face appears to be more convex than seen on male and female teeth of Zapteryx brevirostris (Müller and Henle, 1841) (Rangel et al. 2014) .

Figures

Figure 6. Batoid teeth from the Dry Branch Formation (Priabonian) of Aiken County, South Carolina. A–D. Rhinobatos sp. Tooth in occlusal (A), labial (B), profile (C), and basal (D) views, SC2013.38.45. E–H. Rhynchobatus sp. cf. Rhy. pristinus. Tooth in occlusal (E), labial (F), profile (G), and basal (H) views, SC2013.38.46. I–P. Dasyatis sp. cf. D. tricuspidatus. Male anterior tooth in labial (I) and distal (J) views, SC2013.38.42. Tooth in labial (K) and occlusal (L) views, SC2013.38.43. Tooth in occlusal (M), labial (N), profile (O), and basal (P) views, SC2013.38.41. Q–Y. Dasyatis sp. SC2013.38.49. Male anterior tooth in labial (Q) and distal (R) views. Tooth in occlusal (S) view, SC2013.38.55. Tooth in occlusal (T), labial (U), and profile (V) views, SC2013.38.52. Tooth in occlusal (W), labial (X), and profile (Y) views, SC2013.38.53. Labial at top in A, D, E, H, L, M, P, S–T, W; at left in C, G, J, O, R, V, Y. Scale bars=1 mm.