Nebrius undetermined

Cicimurri, David J. & Knight, James L., 2019, Late Eocene (Priabonian) elasmobranchs from the Dry Branch Formation (Barnwell Group) of Aiken County, South Carolina, USA, PaleoBios 36, pp. 1-31 : 6

NEBRIUS SP. CF. NEB. THIELENSI (WINKLER, 1874)

( FIG. 2F, G )

Referred specimens —SC96.97.1, three incomplete teeth; SC2001.1.41, incomplete tooth; SC2013.38.3, anterior tooth; SC2013.38.4, posterior tooth; SC2013.38.5, anterior tooth ( Fig. 2F, G ); SC2013.38.6, two incomplete teeth.

Remarks —We identify these nine orectolobid teeth as Nebrius because they have a wide crown bearing a central cusp that is flanked by up to seven pairs of lateral cusplets. In contrast, teeth of morphologically similar Ginglymostoma Müller and Henle, 1837 have up to two pairs of lateral cusplets flanking the main cusp ( Herman et al. 1992, Purdy et al. 2001). Unfortunately, identifying fossil Nebrius teeth is often hampered by the fact that original descriptions of fossil species are based on relatively few specimens, and the degree of morphological variation within true biological species is unknown. There is a lack of agreement as to species occurrences within Eocene strata of North America, with Neb.thielensi ( Case and Borodin 2000, Parmley and Cicimurri 2003), Neb. blackenhorni (Stromer, 1903) (Thurmond and Jones 1981), Neb. serra (Manning and Standhardt 1986) , and Neb. obliquus ( Leidy 1877) ( Ginglymostoma obliquum of Case 1981) being recognized in the literature. Kent (1994) reported Neb. thielensi (p. 34, fig. 8.3b) and Neb. blackenhorni (p. 34, fig.8.3a) from the lower Eocene Nanjemoy Formation of Maryland and Virginia ( Kent 1999), and he considered the possibility that the morphologies represented heterodonty within a single species. Woodward (1889: pl. 16, fig. 9) identified teeth from the Eocene of Alabama as Gi. serra ( Leidy 1877) , but Leriche (1942:27, 28) and White (1956:146) synonymized the record with Neb. obliquus. However, Thurmond and Jones (1981:44) reported that the middle Eocene Gosport Sand of Alabama contained a continuous morphological series between the obliquus and serra morphologies, and they synonymized obliquus with serra . Unfortunately, Thurmond and Jones (1981) only provided an illustration of Leidy’s (1877) original material, not specimens from the Gosport Sand. Noubhani and Cappetta (1997) considered the identification of Eocene teeth as Neb. serra to be incorrect and preferred instead to identify teeth as Neb. obliquus (also Darteville and Casier 1943). The precise geologic age of Neb. serra , collected from South Carolina coastal plain deposits is unknown, and the fossils could be as old as Eocene or as young as Pleistocene (see Leidy 1877: pl. 34). Although Neb. obliquus was based on a single tooth from the Eocene of New Jersey, it has been reported as being common in lower Eocene (Ypresian) strata elsewhere (Noubhani and Cappetta 1997, Cappetta 2012).

Morphologically, Neb. thielensi was differentiated from Neb. blackenhorni in having a crown that is wide but rather low, a larger and less distally inclined main cusp, fewer lateral cusplets, and a shorter but conspicuously flat or slightly bifid labial protuberance (Winkler 1874, Arambourg 1952). In contrast, Neb. blackenhorni has a rather high crown in proportion to width, there are ten or more cusplets on the mesial side of the main cusp, and the labial protuberance is more elongated and rounded basally. These generalities are seen in the suite of teeth illustrated in Arambourg (1952, pl. 22), as well as Stromer 1905, and teeth originally identified as Ginglymostoma fourtaui (Priem, 1905) (Priem 1907, 1909).

Noubhani and Cappetta (1997) used features like tooth size, labial crown profile, shape of the labial protuberance, and concavity of the basal attachment surface to separate Neb. thielensi from Neb. obliquus. Some late Eocene records of Nebrius , including teeth identified as Neb. thielensi ( Case and Borodin 2000, Parmley and Cicimurri 2003) and Neb. obliquus ( Case 1981), appear to be conspecific, as all have a large and rather erect main cusp flanked by 7–9 cusplets, and a basal protuberance that is moderately elongated and often weakly bifid. The Dry Branch Nebrius teeth lack enameloid, making direct comparisons to other specimens difficult, but they are comparable to Neb. thielensi (note that the name has also variously been published as Neb. thielensis and Neb. thielense; see Cappetta [2012] for further discussion on spelling) in that they are larger than Neb. obliquus sensu Leidy (1877: pl. 34, fig. 14), have a larger main cusp, fewer lateral cusplets, and shorter and weakly bifid labial protuberance.

Figures

Figure 2. Shark teeth from the Dry Branch Formation (Priabonian) of Aiken County, South Carolina. A–D. Notorynchus sp. cf. No. kempi teeth. Lower left tooth in lingual (A) and labial (B) views, SC2013.38.1. Lower right tooth in labial (C) and lingual (D) views, SC96.97.4. E. Squatina sp. cf. Sq. prima. Antero-lateral tooth in labial view, SC96.97.9. F,G. Nebrius sp. cf. Neb. thielensi. Anterolateral tooth in labial (F) and occlusal (G) views, SC2013.38.5. Labial at top in G. H. Ginglymostomatidae. Tooth in labial view, SC2013.38.7. I–O. Carcharias sp. Third lower right anterior tooth in labial (I) view, SC2001.1.55. Third upper right anterior tooth in lingual (J) and labial (K) views, SC2001.1.57. First lower right anterior tooth in labial (L) view, SC2001.1.59. Second lower right anterior tooth in labial (M) view, SC96.97.44.1. Second upper right anterior tooth in lingual (N) view, SC96.97.42. Lower left lateral tooth in lingual (O) view, SC96.97.43. P–S. Alopias sp. Tooth in labial (P) and lingual (Q) views, SC2001.1.65. Tooth in labial (R) and lingual (S) views, SC2001.1.66. Scale bars=1 cm in A–D, I–K, N, O; 5 mm in E–G, L–M, P–S; 1 mm in H.