RHINOPTERINAE

Cicimurri, David J., Knight, James L. & Ebersole, Jun A., 2022, Early Oligocene (Rupelian) fishes (Chondrichthyes, Osteichthyes) from the Ashley Formation (Cooper Group) of South Carolina, USA, PaleoBios 39 (1), pp. 1-38 : 18

RHINOPTERINAE JORDAN AND EVERMANN, 1896 RHINOPTERA CUVIER, 1829

“ RHINOPTERA ” SP. FIG. 8A, B

Type species — Myliobatis marginata Geoffroy SaintHilaire, 1817 ; Recent; Mediterranean Sea.

2009a Rhinoptera cf. R. studeri ; Cicimurri and Knight, page 641, fig. 6G.

Referred specimen (n=1) —SC2015.29.30.

Remarks —The specimen consists of a broken symphyseal tooth that is very low-crowned, but the crown thickness reflects in vivo usage. The labial and lateral faces overhang the root, but the lingual face is even with the root. There is a thick and rounded transverse ridge located at the crown/root juncture ( Fig. 8B ). These features lead us to conclude that the taxon is more similar to extant Rhinoptera than to Aetomylaeus Garman, 1908 or Myliobatis Cuvier, 1816 , which have expanded root lamellae that extend well beyond the lingual crown margin. Comparison to teeth from the Chandler Bridge Formation that Cicimurri and Knight (2009a) identified as Rhinoptera cf. R. studeri revealed that the material is conspecific.

Recent studies of the evolutionary history of the Myliobatidae by Nelson et al. (2016), Last et al. (2016), and Villalobos-Segura and Underwood (2020) utilized molecular divergence data, which suggested that the clade containing Rhinoptera and Mobula diverged from other Myliobatidae during the early Miocene, and that Rhinoptera diverged from its sister taxon, Mobula , as recently as the late Miocene. Therefore, morphologically similar Paleogene teeth cannot be referred to Rhinoptera . The clade Myliobatidae appears to have its origins during the middle Eocene, and from this time to the Late Oligocene, taxa with teeth morphologically similar to extant Rhinoptera , Myliobatis and Aetomylaeus occur (i.e., Reinecke et al. 2005, Cicimurri and Knight 2009 a, Ebersole et al. 2019). These records must be reevaluated to include both molecular and morphological data to make a more accurate generic determination.

Figures

Figure 8. Batoid teeth from the Givhans Ferry Member, Ashley Formation (Rupelian), Dorchester County, South Carolina. A, B. “Rhinoptera” sp. tooth, SC2015.29.30 in occlusal (A) and lingual (B) views. C, D. “Mobula” sp. male tooth, SC2007.36.40 in apical (C) and occlusal (D) views. E, F. “Mobula” sp. male tooth, SC2007.36.42 in apical (E) and occlusal (F) views. G, H. “Mobu- la” sp. female tooth, SC2007.36.43 in occlusal (G) and labial (H) views. I–K. Plinthicus sp. tooth, SC2007.36.48 in occlusal (I), lingual (J), and profile (K) views. Scale bar=1 mm in C–H; 5 mm in A, B, I–K.