Negaprion gilmorei (Leriche, 1942)

Cicimurri, David J. & Knight, James L., 2022, Late Eocene (Priabonian) elasmobranchs from the Dry Branch Formation (Barnwell Group) of Aiken County, South Carolina, USA, PaleoBios 36, pp. 1-31 : 10

NEGAPRION GILMOREI ( LERICHE 1942)

( FIG. 3Q, R )

Referred specimens —SC96.97.37, upper right anterior tooth; SC96.97.38, upper right antero-lateral tooth; SC96.97.39, upper right lateral tooth; SC96.97.40, 101 upper teeth; SC96.97.41, 24 lower teeth; SC2001.1.47, upper tooth; SC2001.1.48, tooth; SC2001.1.49, lower tooth; SC2001.1.50, 75 teeth; SC2013.38.61, upper anterior tooth; SC2013.38.62, upper right lateral tooth; SC2013.38.63, upper right tooth; SC2013.38.64, lower tooth; SC2013.38.65, seven lower teeth; SC2013.38.66, seven upper anterior teeth; SC2013.38.67, 29 teeth; SC2013.38.68, 14 lower teeth.

Remarks —This species is represented by 267 speci - mens that exhibit dignathic heterodonty, with upper teeth having a broader cusp flanked by elongate, oblique lateral shoulders ( Fig. 3Q ), whereas lower teeth have a shorter and narrower cusp, and smooth shoulders that are nearly perpendicular to the cusp ( Fig. 3R ). Although the enameloid is often missing, the remaining dentine core of the lateral shoulders on some upper teeth shows indications that they were at least weakly serrated.

Leriche (1942) erected Sphyrna gilmorei based on teeth occurring in upper Eocene deposits of Alabama. White (1956) assigned the morphology to the subspecies Negaprion gibbesi gilmorei , and Müller (1999) and Adnet et al. (2007) used the name Carcharhinus gilmorei . Underwood et al. (2011) and Underwood and Gunter (2012) identified unserrated to weakly serrated teeth, such as those reported here, as Negaprion rather than Carcharhinus . If our association is correct, the dignathic heterodonty of Neg. gilmorei is more pronounced than in a dentition of Recent Neg. brevirostris (Poey, 1868) we examined (SC uncurated).

We believe that Eocene material from North Carolina and Georgia that was referred to Neg. eurybathrodon ( Blake, 1862) is more appropriately identified as Neg. gilmorei ( Case1981, Case and Borodin 2000, Parmley and Cicimurri 2003). Teeth of Miocene Neg. eurybathrodon are up to 2 cm in height and width, much larger than Eocene specimens attributed to this species. The main cusp of Neg. eurybathrodon upper teeth is also much taller but narrower than the Eocene specimens, and the lateral shoulders are more evenly serrated (White 1955). Negaprion gilmorei is common in the Dry Branch Formation, and it is the dominant elasmobranch taxon within the Clinchfield Formation of Georgia, based on several thousand teeth within two SC accessions (SC2004.34 and SC2013.44; also Parmley and Cicimurri 2003).

Figures

Figure 3. Carcharhiniform shark teeth the Dry Branch Formation (Priabonian) of Aiken County, South Carolina. A–D. Physogaleus sp. cf. Ph. latus. Upper left lateral tooth in lingual (A) and labial (B) views, SC2013.38.65. Lower left anterior tooth in labial (C) and lingual (D) views, SC96.97.26. E, F. Galeocerdo sp. Anterolateral tooth in lingual (E) and labial (F) views, SC2013.38.16. G–I. Abdounia sp. cf. Ab. enniskilleni. Anterior tooth in lingual (G) and labial (H) views, SC96.97.30. Lateral tooth in lingual (I) view, SC96.97.31. J–L. Rhizoprionodon?ganntourensis. Anterolateral tooth in labial (J) and lingual (K) views, SC2013.38.98. Lateral tooth in lingual view (L), SC2013.38.99. M–P. Hemipristis sp. cf. He. curvatus. Upper left lateral tooth in lingual (M) and labial (N) views, SC2001.1.21. Lower right anterior tooth in lingual (O) and labial (P) views, SC2013.28.35. Q, R. Negaprion gilmorei. Upper right anterior tooth in lingual (Q) view, SC2013.38.61. Lower right anterolateral tooth in lingual (R) view, SC2013.38.64. Scale bars=1 cm in A–F, M–N, Q–R; 5 mm in G–L, O–P.