Carcharhinus elongatus ( Leriche, 1910 )

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 : 33-34

Carcharhinus elongatus ( Leriche, 1910)

Fig. 8I–P, T–V

Sphyrna elongata Leriche, 1910: 300–301 .

Material examined

UNITED STATES OF AMERICA – Mississippi • 291 isolated teeth; Catahoula Formation ; MMNS VP-6627 (92 teeth), SC 2013.28.210 , SC 2013.28.211 ( Fig. 8I–J ), SC 2013.28.212 to 28.214 , SC 2013.28.215 ( Fig. 8K–L ), SC 2013.28.216 to 28.218 , SC 2013.28.219 (6 teeth), SC 2013.28.220 (2 teeth), SC 2013.28.221 (9 teeth), SC 2013.28.222 (7 teeth), SC 2013.28.223 to 28.234 , SC 2013.28.235 ( Fig. 8M–N ), SC 2013.28.236 to 28.238 , SC 2013.28.239 (4 teeth), SC 2013.28.240 (4 teeth), SC 2013.28.241 (6 teeth), SC 2013.28.242 (8 teeth), SC 2013.28.243 , SC 2013.28.244 ( Fig. 8T–V ), SC 2013.28.245 to 28.247 , SC 2013.28.248 (16 teeth), SC 2013.28.249 (7 teeth), SC 2013.28.250 , SC 2013.28.251 ( Fig. 8O–P ), SC 2013.28.252 , SC 2013.28.253 , SC 2013.28.254 (4 teeth), SC 2013.28.255 (7 teeth), SC 2013.28.256 to 28.259 , SC 2013.28.260 (4 teeth), SC 2013.28.261 (7 teeth), SC 2013.28.262 (61 teeth), SC 2013.28.263 (9 teeth).

Description

Two tooth morphologies are present, the most common of which has a broadly triangular main cusp that is flanked by mesial and distal heels ( Fig. 8I–P ). These teeth are typically mesio-distally wider than tall (apico-basally), measuring up to 15 mm and 12 mm, respectively, in these dimensions. However, some specimens are taller than wide. The cusp is broadly triangular, although width differs among the teeth, and it may be vertical but is more often distally inclined. The labial face is virtually flat, whereas the lingual face is convex, and enameloid on both sides is smooth. The mesial and distal cutting edges are smooth and complete along the cusp. The mesial and distal shoulders vary in length, even between the mesial and distal sides of a tooth, and they may be horizontal or oblique. The cutting edges of the shoulders can be serrated, although serration density and size vary, even along a single cutting edge. The shoulders are separated from the main cusp by a tiny notch. The root is low, particularly in labial view, and strongly bilobate. The root lobes are elongated, highly divergent, and separated by a shallow but broad U-shaped or V-shaped interlobe area. The lobes can be described as sub-rectangular with their distal ends ranging from rounded to pointed. The thickened lingual root face is bisected by a wide but shallow nutritive groove that forms a basal notch on some specimens.

The second morphology includes roughly T-shaped teeth. The crowns of these teeth bear a cusp that is somewhat tall and rather narrow, but cusp height varies, and it may be vertical or distally inclined to varying degrees. The cutting edges of these teeth are straight and smooth and extend onto lateral shoulders ( Fig. 8T ). These shoulders may be oblique or perpendicular to cusp height. The root has rather short lobes that are very widely diverging ( Fig. 8U ), with the basal margin being flat to only weakly concave. The lingual nutritive groove is thin and long.

Remarks

Monognathic, dignathic, and ontogenetic heterodonty are represented in our sample of teeth. Upper anterior teeth are taller than wide and symmetrical (or nearly so), whereas lateral teeth are wider than tall and have a distally inclined cusp. Inclination of the main cusp increases towards the jaw commissure and tooth height correspondingly decreases (compare Fig. 8I–J, K–L and M–N ). Upper teeth have a much broader cusp and larger root compared to those in lower files (compare Fig. 8K to U). Lower teeth lack or bear only very weak serrations on the lateral shoulders, and the basal root margin is straighter (compare Fig 8T to O). Ontogenetic heterodonty is expressed as a difference in stoutness among the different tooth size classes, with small teeth being relatively gracile (presumed juveniles) compared to the large, robust specimens (presumed adults). Serration size and density on the lateral shoulders is also variable and may be virtually absent ( Fig. 8O ), weakly developed ( Fig. 8M ), or strongly developed ( Fig. 8I ). However, this does not appear to reflect monognathic heterodonty or ontogeny. Rather, it is variation among individual teeth in each file, as a particular serration size or density (or lack thereof) is not indicative of any specific jaw position, and small teeth (juveniles) exhibit the same variation as large (adult) teeth.

The teeth described above fall within the size range of Carcharhinus elongatus ( Leriche, 1910) and C. gibbesii ( Woodward, 1889) (see Reinecke et al. 2014), species that have been reported from the Oligocene of North America and Europe ( Reinecke et al. 2001, 2005; Cicimurri & Knight 2009; Cicimurri et al. 2022). However, the teeth of C. gibbesii appear to have coarse and uniformly serrated lateral heels, whereas the heels of C. elongatus are irregularly serrated (similar to the condition in Physogaleus ) or even smooth. We identify the Catahoula Formation teeth as C. elongatus because the serrations are much weaker (or altogether absent) compared to C. gibbesii . Reinecke et al. (2014) indicated that some Oligocene teeth represent a transitional species between C. elongatus and C. gibbesii , although this intermediate species has yet to be determined. Müller (1999) reported C. elongatus from the Oligocene Old Church Formation of Virginia, but we concur with Cicimurri et al. (2022) that the coarse serration pattern of the teeth he illustrated (pl. 6 figs 5–9) is more like that of C. gibbesii . Müller (1999) also reported C. elongatus and C. gibbesii from the Ashley Formation of South Carolina, but he did not illustrate any specimens, and we could not verify their identity.

Figures

Fig. 8. Rhizoprionodon sp. (A–D), Carcharhinus acuarius (Probst, 1879) (E–H, Q–S), and C. elongatus (Leriche, 1910) (I–P, T–V), teeth. A–B. SC2013.28.145, Rhizoprionodon sp., upper right anterior tooth. A. Labial view. B. Lingual view. C–D. SC2013.28.148, Rhizoprionodon sp., lower right lateral tooth. C. Labial view. D. Lingual view. E–F. SC2013.28.195, Carcharhinus acuarius, upper right lateral tooth. E. Labial view. F. Lingual view. G–H. SC2013.28.194, C. acuarius, upper right anterior tooth. G. Labial view. H. Lingual view. I–J. SC2013.28.211, C. elongatus, upper left anterolateral tooth. I. Labial view. J. Lingual view. K–L. SC2013.28.215, C. elongatus, upper left lateral tooth. K. Labial view. L. Lingual view. M–N. SC2013.28.235, C. elongatus, upper right posterolateral tooth. M. Labial view. N. Lingual view. O–P. SC2013.28.251, C. elongatus, upper right lateral tooth. O. Labial view. P. Lingual view. Q–S. SC2013.28.201, C. acuarius, lower tooth. Q. Labial view. R. Lingual view. S. Mesial view. T–V. SC2013.28.244, C. elongatus, lower tooth. T. Labial view. U. Lingual view. V. Mesial view. Scale bars: A–B = 3 mm; C–D = 2 mm; E–V = 5 mm.