Early Oligocene (Rupelian) fishes (Chondrichthyes, Osteichthyes) from the Ashley Formation (Cooper Group) of South Carolina, USA Author Cicimurri, David J. Author Knight, James L. Author Ebersole, Jun A. text PaleoBios 2022 2022-03-31 39 1 1 38 http://dx.doi.org/10.5070/p939056976 journal article 10.5070/P939056976 0031-0298 13743778 13E6A6E9-DE0F-4C71-BE40-2957F48D9F70 “ MOBULA ” SP. FIG. 8C–H Type species — Mobula auriculata Rafinesque, 1810b ; Recent. 1999 Mobula sp. ; Müller, page 66. 2009a Mobula cf. M. loupianensis Cappetta, 1970 ; Cicimurri and Knight, pages 639–640, fig. 9. Referred specimens (n=11) —SC2007.36.40 ( Fig. 8C, D ), SC2007.36.41, SC2007.36.42 ( Fig. 8E, F ), SC2007.36.43 ( Fig. 8G, H ), SC2007.36.44, SC2007.36.45, SC2007.36.46, SC2007.36.47, SC2007.36.125, SC2015.29.16, SC2015.29.31. Remarks —A recent molecular divergence study by Villalobos-Segura and Underwood (2020) suggested that Mobula diverged from its sister taxon, Rhinoptera , during the late Miocene. This suggests that morphologically similar Paleogene teeth cannot be referred to Mobula . However, the great similarity of the Oligocene taxon to both M. loupianensis and extant M. rochebrunei ( Vaillant, 1879 ) would seem to indicate a close phylogenetic relationship. The Oligocene mobulids from South Carolina are being investigated in more detail, but for the purposes of this report we conservatively retain these specimens within the genus Mobula with the understanding that they likely belong to a closely related ancestral taxon. Our small sample exhibits a remarkable amount of variation, which we attribute to gynandric heterodonty within a single taxon (see Notabartolo di Sciara 1987 ). The narrow, single to tri-cusped teeth represent males, whereas the wider, linguiform to multi-cuspidate teeth belong to females. This interpretation is supported by the work of Herman et al. (2000 , plates 19–22), who illustrated the gynandric variation they observed in extant Mobula rochebrunei . The Ashley Formation morphotypes we examined match those illustrated by Cicimurri and Knight (2009a , fig. 9) from the overlying (Chattian) Chandler Bridge Formation, and we regard them as conspecific. We also concur with Cicimurri and Knight (2009a) that the Mobula sp. teeth reported by Müller (1999) from the Oligocene Old Church Formation of Virginia appear to fall within the range of variation observed in the South Carolina Oligocene “ Mobula ” sample. Müller (1999 , page 66) reported Mobula sp. from the Ashley Formation, but he did not illustrate any specimens from this lithostratigraphic unit. Although some of the South Carolina Oligocene “ Mobula ” teeth resemble the holotype of the Rupelian Mobula irenae Pfeil, 1981 , none are similar to Pfeil’s (1981 :plate 1, fig. 2) paratype , and we consider the two as separate species. The Rupelian taxon Eomanta kowaldi Pfeil, 1981 is based on a single tooth and there is some debate as to whether it represents a distinct taxon ( Adnet et al. 2012 ) or is conspecific with “ M .” irenae ( Cicimurri and Knight 2009a ) . The E. kowaldi tooth has a higher crown and the occlusal surface is unusually constricted and more embayed compared to our Oligocene specimens. The early Eocene (Ypresian) taxon Eomobula Herman et al., 1989 may not be a mobulid as originally thought ( Adnet et al. 2012 ), but the superficially similar teeth can be differentiated from the South Carolina Oligocene specimens by its very low crown with no vertical wrinkling, and the root is poorly differentiated into individual root lobes. The taxon Paramobula fragilis ( Cappetta, 1970 ) (which has since been assigned to Mobula ) was reported from the Chattian Chandler Bridge Formation by Cicimurri and Knight 2009a (fig. 6D), but these teeth are more similar in morphology to those of Plinthicus and will not be confused with “ Mobula ” teeth described herein. Eocene and Oligocene teeth of Argoubia Adnet et al., 2012 apparently lack the linguiform and bi- and tri-cuspidate morphologies that occur in the dentition of the Ashley Formation taxon, and the occlusal surface is generally weakly concave (also Leder 2015 ). Eocene Oromobula Adnet et al., 2012 teeth generally are higher and much thinner (labio-lingually) than the South Carolina “ Mobula ,” and the relatively small occlusal surface is very irregular.