Carcharhinus gibbesi (Woodward, 1889)

Cicimurri, David J. & Knight, James L., 2009, Late Oligocene sharks and rays from the Chandler Bridge Formation, Dorchester County, South Carolina, USA, Acta Palaeontologica Polonica 54 (4), pp. 627-647 : 632

Carcharhinus gibbesi (Woodward, 1889)

Fig. 5A–D .

Referred specimens.—BCGM 9056–9062, SC 2009.18.6.

Comments.—This taxon is the most abundant non−batomorph elasmobranch in the Chandler Bridge sample. We assign two morphologies to C. gibbesi ; one has a broadly triangular, smooth−edged cusp flanked by serrated mesial and distal shoulders ( Fig. 5A–C ), the other has a narrower cusp flanked by low, smooth−edged heels ( Fig. 5D ). We concur with White (1956: 143, text−figs. 77–94) and regard the former morphology as representing upper teeth, whereas the latter represents lower teeth (dignathic heterodonty). Upper teeth of C. gibbesi are similar to those of C. elongatus ( Leriche, 1910) , but the latter species may be distinguished by the more weakly serrated or smooth lateral shoulders ( Génault 1993; Baut and Génault 1999; Reinecke et al. 2001, 2005; Haye et al. 2008). Cutting edges on the lower teeth of our C. gibbesi are completely smooth, whereas those of C. elongatus may be weakly serrated (see Reinecke et al. 2001: pls. 50, 52; Reinecke et al. 2005: pl. 39).

There is little indication of ontogenetic heterodonty in our sample, as small teeth from each jaw position are simply miniature versions of their adult counterparts (compare Fig. 5A to 5B). Monognathic heterodonty is more obvious in upper teeth, with specimens from anterior positions being more symmetrical ( Fig. 5B ), but cusps become more distally directed and lateral shoulders more elongated towards the commissure ( Fig. 5C ). Only in more distal positions are the cusps of lower teeth distally directed.

We believe that the gibbesi material described and illustrated by White (1956: 143, text−figs. 77–94) that came from the “phosphate beds” of South Carolina were derived from Oligocene as opposed to Eocene strata. We have thus far only recovered this morphology from the Ashley and Chandler Bridge formations, but the upper Eocene (Priabonian) Harleyville Formation contains the similar, but more weakly serrated (usually unserrated), Carcharhinus gilmorei ( Leriche, 1942) . Eocene C. gilmorei have variously been referred to in the literature as Sphyrna gilmorei Leriche, 1942 , Negaprion gibbesi gilmorei ( Leriche, 1942) (see White 1956), N. eurybathrodon (Blake, 1862) (i.e., Case 1981; Parmley and Cicimurri 2003), and C. gibbesi gilmorei ( Leriche, 1942) (i.e., Kruckow and Thies 1990; Manning 2006). Manning (2006) noted that C. gilmorei and C. gibbesi morphologies occur together in Oligocene but not Eocene strata (no C. gibbesi ) of the Gulf Coastal Plain, and that the morphologies were intergradational. Müller (1999) reported both C. gibbesi and C. elongatus from Oligocene deposits of the Atlantic Coastal Plain. We recovered several upper teeth that are quite similar to Carcharhinus gilmorei and C. elongatus , but we consider these specimens to represent morphological variation within C. gibbesi , not an additional species/subspecies.

Stratigraphic and geographic range.—Oligocene (Chattian), USA (Gulf and Atlantic coastal Plains).

Figures

Fig. 5. Carcharhiniform sharks from Summerville, upper Chattian. A–D. Carharhinus gibbesi (Woodward, 1889). A. BCGM 9059, juvenile upper anterior tooth, labial view. B. BCGM 9060, adult upper anterior tooth, labial view. C. BCGM 9061, juvenile upper lateral tooth, labial view. D. BCGM 9058, adult lower anterior tooth, labial view. E, F. Physogaleus aduncus (Agassiz, 1835). E. BCGM 9064, upper lateral tooth, labial view. F. BCGM 9066, lower anterior tooth, labial view. G. Physogaleus sp., BCGM 9068, antero−lateral tooth, labial view. H. Rhizoprionodon sp., BCGM 9070, labial view. I, J. Hemipristis serra (Agassiz, 1835). I. BCGM 9073, adult upper lateral tooth, labial view. J. BCGM 9072, juvenile upper lateral tooth, labial view. K. Sphyrna cf. S. media Springer, 1940, BCGM 9077, lateral tooth, labial view. L. Sphyrna zygaena (Linneaus, 1758), BCGM 9079, lateral tooth, lingual view. M. Bythaelurus sp., BCGM 9074, labial view. N–P. Galeorhinus sp. N. BCGM 9081, parasymphyseal tooth, labial view. O. BCGM 9082, antero−lateral tooth, labial view. P. BCGM 9083, lateral tooth, labial view.