Physogaleus aduncus (Agassiz, 1843)

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 : 632-633

Physogaleus aduncus (Agassiz, 1843)

Fig. 5E, F .

Referred specimens.—BCGM 9063–9066, SC 2009.18.7.

Comments.—The teeth within in this sample include morphotypes traditionally identified as Galeocerdo contortus Gibbes, 1849 and G. aduncus Agassiz, 1843 . Our studies of Oligocene and Miocene elasmobranch assemblages from the Atlantic Coastal plain confirm the observations of Purdy et al. (2001) and Ward and Bonavia (2001) that the two morphotypes occur together and in nearly equal numbers (see also Case 1980; Kent 1994). The morphologies could represent two coeval species, the teeth might be conspecific and represent dignathic heterodonty in a single species, (upper and lower teeth), or the teeth may be conspecific and represent gynandric heterodonty (male and female teeth).

Leriche (1927) illustrated what appear to be the “ G. contortus ” and “ G. aduncus ” morphologies under the name Galeocerdo aduncus (pl. 14: 1–8). Applegate (1978, 1992) discussed the possibility that the two morphologies represent dignathic heterodonty within a single species, “ G. ” aduncus , with palatoquadrates (upper jaws) bearing the “ G. aduncus ” morphotype and the Meckel’s cartilages (lower jaws) the “ G. contortus ” morphotype. Gottfried (1993) followed Applegate (1978) when describing a dentigerous partial right Meckel’s cartilage from the Miocene of Maryland, and Manning (2006) also advocated this relationship. Treating the morphologies as separate species, Purdy et al. (2001) suggested that “ G. aduncus ” fed on larger animals, whereas “ G. contortus ” was piscivorous.

Ward and Bonavia (2001) consider the “ G. contortus ” and “ G. aduncus ” morphologies to represent the same species (“ G. aduncus ”), but they also believe these are sufficiently similar to another carcharhiniform shark, Physogaleus Cappetta, 1980 , to warrant placement in that genus. Reinecke et al. (2005) assigned the contortus morphology to Physogaleus , but they referred the G. aduncus morphology to Galeocerdo , citing differences in tooth morphology and the paucity or complete lack of the G. contortus morphology in deposits yielding the G. aduncus morphology (see also Reinecke and Hoedemakers 2006). Physogaleus exhibits gynandric heterodonty ( Cappetta 1987), and according to Ward and Bonavia’s (2001) taxonomy the typical G. aduncus morphology represents teeth of females and upper teeth of males ( Fig. 5E ), whereas the G. contortus morphology represents teeth in the lower dentition of males ( Fig. 5F ). The taxonomic questions raised by the G. contortus / G. aduncus associations may not be answered without the aid of numerous crania with articulated dentitions (showing the range of gynandric/dignathic heterodonty).

Stratigraphic and geographic range.—Oligocene to Pliocene, Europe, USA (Atlantic Coastal Plain), Japan, Equador, Zaire.

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.