Raja mccollumi, Cicimurri & Knight, 2009

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 : 636-637

Raja mccollumi sp. nov.

Fig. 7C, D, F–H .

Etymology: Species named in honor of Vance McCollum of Summerville, SC, for helping to increase our understanding of an upper Oligocene ecosystem, and for his efforts in broadening our knowledge of South Carolina vertebrate paleontology over the last two decades.

Type material: Holotype: BCGM 9093 , male anterior tooth , Paratypes: BCGM 9199 , male lateral tooth , BCGM 9200 , female anterior tooth, 9201, female lateral tooth , BCGM 9202 , female posterior tooth .

Type locality: Summerville , Dorchester County, South Carolina, USA .

Type horizon: marine facies of Katuna et al. (1997), Chandler Bridge Formation, upper Chattian (upper part of calcareous nannofossil zone NP 25), Oligocene.

Referred specimens.—BCGM 9090, SC 2009.18.15.

Diagnosis.—A fossil species in which male teeth bear a tall, narrow cusp; anterior teeth are symmetrical to weakly asymmetrical; the cusp is conical to slightly laterally compressed and lacks a labial cutting edge. In contrast, male anterior teeth of Oligo−Miocene R. cecilae Steurbaut and Herman, 1978 can be strongly asymmetrical, and the cusp is very laterally compressed with a conspicuous labial cutting edge ( Hovestadt and Hovestadt−Euler 1995; Reinecke et al. 2005, 2008; Haye et al. 2008). The labial crown margin of R. cecilae is also narrower and more labio−basally directed. Female teeth of R. mccollumi sp. nov. differ from R. cecilae in that the labial face of R. cecilae is flat to weakly concave, and the root is larger ( Hovestadt and Hovestadt−Euler 1995; Reinecke et al. 2005, 2008; Haye et al. 2008). Although of similar size, the cusp of male teeth of Miocene Raja gentilli Joleaud, 1912 has a broader base, and the marginal area is smaller ( Ward and Bonavia 2001) than male R. mccollumi sp. nov. Male teeth of R. mccollumi sp. nov. are smaller than Oligo−Miocene R. casieri Steurbaut and Herman, 1978 and Miocene R. olisiponensis (Jonet, 1968) , and lack the conspicuous mesial and distal cutting edges seen on male teeth of the latter two taxa. Raja sp. from the German Chattian differ from male R. mccollumi sp. nov. in having a wider cusp ( Reinecke et al. 2005: pl. 53: 1, 3; Haye et al. 2008: pl. 9: 4). Teeth of Raja sp. 1 described by Müller (1999: 56, text−fig. 18, nos. 7–10) may be conspecific with R. mccollumi sp. nov., but this determination must await our examination of specimens from the Ashley Marl.

Description.—Male teeth are strongly cuspidate, especially in anterior positions. The cusp is lingually curved and conical to laterally compressed. The labial cusp face is very convex and lacks a cutting edge, whereas the lingual face is flatter and bears inconspicuous mesial and distal cutting edges, neither of which extend onto the crown base. The crown base is roughly circular in outline, with a rounded to slightly flattened labial margin. The lingual crown margin is formed into a basally directed uvula that is broadly concave. In labial view, the crown becomes asymmetrical towards the commissure in that the cusp is offset distally as well as more distally inclined. Additionally, the cusp is often more laterally compressed but still lacks a labial cutting edge, and the labial crown base is more irregular. Closer to the commissure, the cusp becomes lower and even more strongly directed lingually.

Female teeth are easily distinguished from males in that the lingually directed cusp is very low and the labial face is broadly triangular. The cusp is longest in anterior jaw positions, but it becomes reduced towards the commissure and is indistinct in posterior positions. In labial view, anterior teeth are slightly asymmetrical because the cusp is distally inclined, but towards the commissure the cusp becomes offset distally and more obviously distally inclined. In all jaw positions, mesial and distal cutting edges extend from the crown base to the cup apex, dividing the crown into a large labial face and much smaller lingual face. In lateral view, the outline of the labial face of anterior and antero−lateral teeth is sinuous because it is medially concave, and the labial crown margin greatly overhangs the root. The labial face is flatter in more distal jaw positions, and the labial crown margin is not as pronounced. The lingual uvula is very small.

Tooth roots are rather low and bilobate. Root lobes flare outward from the base of the crown, and are separated by a deep nutritive groove. Basal attachment surfaces are triangular, flat, and may be narrow or broad.

Comments.—The morphological variation in our sample is interpreted to represent sexual (compare Fig. 7C and F ) and monognathic (compare Fig. 7C and D, F and G ) heterodonty. However, the monognathic heterodonty envisioned in male and female dentitions of R. mccollumi sp. nov. appears to have been gradational and similar to R. laevis Garman, 1913 (see Bigelow and Schroeder 1953), whereas monognathic heterodonty in R. cecilae is disjunct. Male and female teeth of R. mccollumi sp. nov. are nearly equally represented, and the taxon is the most common elasmobranch in our Chandler

Bridge sample. Stratigraphic and geographic range.—Oligocene (Chattian),

USA (South Carolina).

Figures

Fig. 7. Skates from Summerville, upper Chattian. A, B, Raja sp. A. BCGM 9088, male anterior tooth, occlusal (A1), lateral (A2), and lingual (A3) view. B. BCGM 9089, female lateral tooth, labial (B1) and lateral (B2) view. C, D, Raja mccollumi sp. nov. C. BCGM 9093 (holotype), male anterior tooth, occlusal (C1), lateral (C2), labial (C3), and lingual (C4) view. D. BCGM 9199 (paratype), male lateral tooth, basal (D1), lateral (D2), lingual (D3) view. E. BCGM 9095, Raja sp. denticle, lateral−oblique view. F–H, R. mccollumi sp. nov. F. BCGM 9200 (paratype), female anterior tooth, occlusal (F1), labial (F2), and lingual (F3) view. G. BCGM 9201 (paratype), female lateral tooth, labial (G1) and lingual (G2) view. H. BCGM 9202 (paratype), female posterior tooth, occlusal (H1), labial (H2), lingual (H3) view.