Rhynchobatus cf. pristinus ( Probst, 1877 )

Cicimurri, David J., Ebersole, Jun A., Stringer, Gary L., Starnes, James E. & Phillips, George E., 2025, Late Oligocene fishes (Chondrichthyes and Osteichthyes) from the Catahoula Formation in Wayne County, Mississippi, USA, European Journal of Taxonomy 984 (1), pp. 1-131 : 49-51

Rhynchobatus cf. pristinus ( Probst, 1877)

Fig. 13G–L

Xxx pristinus Probst, 1877: 81–82 .

Material examined

UNITED STATES OF AMERICA – Mississippi • 246 isolated teeth; Catahoula Formation ; MMNS VP-7747 (16 teeth), MMNS VP-7754 (33 teeth), MMNS VP-12078 , SC 2013.28.494 , SC 2013.28.495 , SC 2013.28.496 ( Fig. 13G–I ), SC 2013.28.497 to 28.499 , SC 2013.28.500 ( Fig. 13J–L ), SC 2013.28.501 , SC 2013.28.502 , SC 2013.28.503 (7 teeth), SC 2013.28.504 (17 teeth), SC 2013.28.505 (7 teeth), SC 2013.28.506 (14 teeth), SC 2013.28.507 (20 teeth), SC 2013.28.508 (42 teeth), SC 2013.28.509 (28 teeth), SC 2013.28.510 (15 teeth), SC 2013.28.511 (36 teeth), SC 2013.28.526 .

Description

In occlusal view, the main body of the tooth crown is usually wider than long, with larger specimens measuring 4 mm in mesio-distal width. The occlusal outline of these teeth is sub-rectangular, with the labial margin being convex and the sides straight or slightly angled medially ( Fig. 13H, K ). Some teeth have a circular occlusal outline. The labial and lingual faces are separated by a transverse crest that varies in size, and the convex labial face is coarsely tuberculated ( Fig. 13G–H ). These tubercles sometimes appear to coalesce into discontinuous ridges. The apical part of the lingual surface is flat and has a triangular outline, and unworn teeth have a tuberculated appearance. This surface transitions to a smooth, convex portion of the lingual face. The sides of the lingual crown foot are formed into thin, shelf-like projections. There is a pronounced medial uvula that extends onto the root surface. The uvula may be short and wide or narrow and elongated (compare Fig. 13H to K). In profile view, the labial crown foot overhangs the low root, and the root extends slightly beyond the lingual crown foot ( Fig. 13I, L ). In basal view, the root is obviously bilobate, with the somewhat triangular lobes being separated by a longitudinal nutritive groove. The basal attachment surfaces are flat to weakly convex. In occlusal view, the root bears margino-lingual foramina that flank the crown uvula, and the lingual root projection has a notched appearance.

Remarks

Various tooth sizes and slightly differing morphologies occur in our sample, but we attribute these minor differences to heterodonty. Specimens with a circular occlusal outline may represent symphyseal or anterior positions and those with a more rectangular outline are from lateral files (monognathic heterodonty). Variation in tooth size could reflect ontogenetic heterodonty (i.e., juvenile versus adult individuals) or even dignathic heterodonty, given the unusual configuration of the Rhynchobatus dentition (see Dean et al. 2017: figs 1–2). Crown ornamentation is difficult to discern on many specimens, which in part is the result of post mortem ablation (i.e., current transport) but also in vivo wear (which is particularly evident at the crown apex).

These teeth are significantly larger and more robust than those of Pristis sp. , described below, and they possess labial ornamentation but lack lingual lateral uvulae. Cicimurri & Knight (2009) reported four teeth from the Chattian Chandler Bridge Formation of South Carolina that they tentatively identified as Rhynchobatus pristinus , and the species was noted in the Oligocene Old Church Formation of Virginia ( Müller 1999) and the Oligo-Miocene Belgrade Formation of North Carolina ( Case 1980; Müller 1999). Cicimurri et al. (2022) reported a few teeth from the Rupelian Ashley Formation that were identified as Rhynchobatus sp. Most of the Catahoula Formation specimens are ablated, but well-preserved teeth fall within the range of variation of R. pristinus and are tentatively referred to that species. Rhynchobatus pristinus apparently had a wide distribution in the Western Hemisphere ( Cappetta 1970; Laurito 1999; Ward & Bonavia 2001; Vialle et al. 2011; Fialho et al. 2019), but the specimens noted in the aforementioned reports are variable and it remains to be determined whether all of these records are accurately attributed to R. pristinus . It is interesting to note that all of the Oligocene records known to us are from the Atlantic Coastal Plain of the USA, and the teeth in our sample represent the first occurrences of fossil Rhynchobatus in the Gulf Coastal Plain of the USA.

Figures

Fig. 13. Pristis sp. (A–F, M–R), Rhynchobatus cf. pristinus (Probst, 1877) (G–L), and Anoxypristis sp. (S–X), teeth and rostral spines. A–C. SC2013.28.490, Pristis sp., tooth. A. Oro-lingual view. B. Labial view. C. Profile view. D–F. SC2013.28.486, Pristis sp., tooth. D. Oro-lingual view. E. Labial view. F. Profile view. G–I. SC2013.28.496, Rhynchobatus cf. pristinus, tooth. G. Labial view. H. Occlusal view. I. Profile view. J–L. SC2013.28.500, R. cf. pristinus, tooth. J. Labial view. K. Occlusal view. L. Profile view. M–O. MMNS VP-12070, Pristis sp., right rostral spine. M. Basal view. N. Posterior view.O. Dorsal view.P–R. MMNS VP-7787.1,Pristis sp., right rostral spine.P. Basal view.Q. Posterior view. R. Dorsal view. S–U. MMNS VP-12071, Anoyxpristis sp., right rostral spine. S. Basal view. T. Posterior view. U. Dorsal view. V–X. MMNS VP-12072.1, Anoxypristis sp., right rostral spine. V. Basal view. W. Posterior view. X. Dorsal view. Scale bars: A–F = 1 mm; G–L = 3 mm; M–X = 1 cm.