Physogaleus, CAPPETTA, 1980

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 : 10

PHYSOGALEUS CF. P. CONTORTUS ( GIBBES, 1849)

FIG. 5D

Type species — Trigonodus secundus Winkler, 1874 ; middle Eocene , Belgium .

1849 Galeocerdo contortus Gibbes ; p. 193, pl. 25, figs. 71 – 74, Eocene(?) and Miocene, South Carolina and Virginia.

2009a Physogaleus aduncus ( Agassiz, 1835) ; Cicimurri and Knight, p. 632–633, fig. 5F.

Referred specimens (n=6) —SC2007.36.19 ( Fig. 5D ), SC2007.36.20 (four teeth), SC2015.29.27.

Remarks —When Gibbes (1849) originally named and referred the contortus morphology to Galeocerdo (page 193), he did not designate a type specimen, type locality, or a type horizon/age. Gibbes (1849) stated that his sample included teeth from the Eocene of South Carolina and the Miocene of Virginia, but, unfortunately, he did not indicate which, if any, of the specimens shown in his plate XXV (figs. 71–74) were from South Carolina. Additionally, the Eocene age of Gibbes’ (1849) South Carolina specimens is questionable because he included the site among his “Upper or Newer Eocene” localities (page 121). South Carolina invertebrate fossils that Gibbes (1849) noted as occurring in “Upper or Newer Eocene” beds, including Cubitostrea sellaeformis ( Conrad, 1832) , are found in the middle Eocene (Lutetian) Santee Limestone in the Coastal Plain. However, this unit seems unlikely as the source of the contortus specimens, as the morphology is currently unknown from the Santee Limestone (DJC personal observation), and it does not occur in temporally equivalent deposits in Alabama ( Ebersole et al. 2019). Moreover, many of the invertebrate taxa Gibbes (1849) listed in his “Upper or Newer Eocene” division occur in what we now know to be lower Oligocene (Rupelian) strata of the Vicksburg Group in the Gulf Coastal Plain. It is therefore possible that the South Carolina contortus specimens available to Gibbes were derived from the Ashley Formation. The contortus morphology has more recently been referred to Physogaleus (see additional discussion below) and is followed herein.

The Ashley Formation specimens were compared to material from the Chattian Chandler Bridge Formation (SC2005.2) and middle Miocene Pungo River Formation (SC98.46), and all the specimens share the conspicuous “twisted” mesial cusp edge that Gibbes (1849) noted as being characteristic of his contortus species. For this reason, we tentatively assign the incompletely preserved Ashley Formation specimens to P. contortus . However, although quite similar, we note that the Oligocene specimens from South Carolina are significantly smaller than the Miocene specimens. Additional study is needed to determine if the Oligocene and Miocene species are indeed different, or if variation, like tooth size, is related to phyletic increase through time within a single species, as has been suggested for Hemipristis serra ( Chandler et al. 2006) and Striatolamia macrota ( Agassiz, 1838) ( Cappetta 2012, Ebersole et al. 2019). Should the material be conspecific, a neotype specimen with associated age (Oligocene or Miocene) and stratigraphic occurrence (Ashley Formation?) must be determined. In turn, if the Oligocene and Miocene teeth represent distinct species, it must be determined which morphology truly represents P. contortus and which should be designated a new species.

Physogaleus contortus , as currently defined, clearly differs from Galeocerdo aduncus ( Agassiz, 1835) (see below) by having a much more elongated and narrower main cusp that appears twisted in mesial view. Additionally, the mesial serrations are much finer and simple to only weakly compound, the distal cutting-edge serrations are finer. In addition, the distal heel is often marked by a rounded angle rather than distinct notch, and the distal heel has more denticles that are smooth to weakly serrated only on the mesial edge.

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.