SPHYRNIDAE BONAPARTE, 1840

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 : 11

SPHYRNIDAE BONAPARTE, 1840

GEN. ET SP. INDET.

FIG. 5G, H

2009a Sphyrna cf. S. media Springer, 1940 ; Cicimurri and Knight, page 635, fig. 5K.

2009a Sphyrna zygaena ( Linnaeus, 1758) ; Cicimurri and Knight, page 635, fig. 5L.

Referred specimens (n=20) —SC2007.36.23, SC2007.36.24 ( Fig. 5H ), SC2007.36.25 (11 teeth), SC2007.36.26 ( Fig. 5G ), SC2007.36.27, SC2007.36.28 (five teeth).

Remarks —Two morphologies that have previously been assigned to Sphyrna Linnaeus, 1758 , are present in our sample. The first morphology, represented by specimens SC2007.36.23–.25, was reported from the Chattian Chandler Bridge Formation by Cicimurri and Knight (2009a), who tentatively identified it as Sphyrna media Springer, 1940 . The second morphology, represented by specimens SC2007.36.26–.28, was identified by Cicimurri and Knight (2009a) as Sphyrna zygaena ( Linnaeus, 1758) because specimens were comparable to Mio-Pliocene teeth identified by Purdy et al. (2001). In their study, Purdy et al. (2001) synonymized fossil S. laevissima ( Cope, 1867) with extant S. zygaena , citing that the tooth morphologies were indistinguishable.

Although the South Carolina Oligocene material appears to be similar to teeth of extant Sphyrna species, assigning the fossil morphologies to this genus is somewhat problematic. In a phylogenetic analysis, Lim et al. (2010) determined that the divergence of Sphyrna and its sister taxon, Eusphyra Gill, 1862 , occurred during the Miocene, between 15 and 20 million years ago, and that diversification within Sphyrna occurred only within the past 10 million years. The South Carolina Oligocene teeth are comparable and can be assigned to Sphyrnidae , as Lim et al. (2010) has indicated that the family diverged from Carcharhinus during the middle Eocene. However, based on the divergence times proposed by Lim et al. (2010), the Rupelian and Chattian teeth should not be assigned to Sphyrna , let alone any of the extant species. Although Carrillo-Briceño et al. (2020) and Adnet et al. (2020) have recently assigned Oligocene and Eocene (respectively) teeth to Sphyrna , the work of Lim et al. (2010) should not be discounted. We believe that the South Carolina Oligocene teeth could represent one or more undescribed stem members of the family, but such a determination is beyond the scope of this paper.

Figures

Figure 5. Selachian teeth from the Givhans Ferry Member, Ashley Formation (Rupelian), Dorchester County, South Carolina. A. Hemipristis cf. H. serra tooth, SC2007.36.7 in labial view. B. Carcharhinus gibbesi upper tooth, SC2007.36.14 in labial view. C. Carcharhinus gibbesi lower tooth, SC2007.36.15 in labial view. D. Physogaleus cf. P. contortus tooth, SC2007.36.19 in labial view. E. Physogaleus sp. tooth, SC2007.36.21 in labial view. F. Galeocerdo aduncus tooth, SC2007.36.17 in labial view. G. Sphyrnidae Morphotype 1 tooth, SC2007.36.26 in labial view. H. Sphyrnidae Morphotype 2 tooth, SC2007.36.24 in labial view. Scale bar=3 mm in E; 5 mm in A, C, D, F, G; 10 mm in B.