Carcharhinus acuarius ( Probst, 1879 )

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 : 31-33

Carcharhinus acuarius ( Probst, 1879)

Fig. 8E–H, Q–S

Alopecias acuarius Probst, 1879: 140 .

Material examined

UNITED STATES OF AMERICA – Mississippi • 986 isolated teeth; Catahoula Formation ; SC 2013.28.188 to 28.193 , SC 2013.28.194 ( Fig. 8G–H ), SC 2013.28.195 ( Fig. 8E–F ), SC 2013.28.196 to 28.200 , SC 2013.28.201 ( Fig. 8Q–S ), SC 2013.28.202 to 28.204 , SC 2013.28.205 (149 teeth), SC 2013.28.206 (206 teeth), SC 2013.28.207 (169 teeth), SC 2013.28.208 (305 teeth), SC 2013.28.209 (121 teeth), SC 2013.28.266 (3 teeth), SC 2013.28.267 (16 teeth).

Description

The largest teeth in our sample measure 10 mm in apico-basial height and 8 mm in mesio-distal width. The crown consists of a cusp and low lateral shoulders. The cusp varies considerably in height and width, ranging from tall and narrow (mesio-distally) to rather low and broad. In profile the tall and narrow teeth have a slight lingual curvature, but broader teeth are erect. The labial face is flat to weakly convex, whereas the lingual face is convex. The crown enameloid is smooth. The mesial and distal cutting edges are smooth and extend from the cusp apex and onto the lateral shoulders. The shoulders are rather low, vary in length (even between the mesial and distal sides of a given tooth), and may be straight to somewhat convex. The root is bilobate with the lobes being elongated, narrow and somewhat closely spaced, or somewhat rectangular and widely diverging. The U-shaped interlobe area is correspondingly deep or shallow. The thickened lingual root face is bisected by a long and deep nutritive groove.

Remarks

We observed variation in tooth shape and size in the Catahoula Formation sample that we believe reflects heterodonty within a single species. A parasymphyseal tooth (i.e., located adjacent to the jaw symphysis) is small in overall size, has a tall and narrow crown and robust root with short lobes, and the root is equal in height to the crown (see an equivalent tooth in Cappetta 1970: pl. 17). Anterior teeth have a tall and narrow cusp with elongated root lobes, and the lateral shoulders are rather short and oblique. Lateral teeth have a somewhat broader and lower cusp, the lateral shoulders are more elongated and perpendicular to cusp height, and the shorter root lobes are more rectangular and widely diverging. Upper anterior teeth ( Fig. 8G–H ) have shorter root lobes compared to lower anteriors. Upper lateral teeth have broader and more distally inclined cusps than lower laterals (compare Fig. 8E–F to Q–S). We also observed ontogenetic heterodonty in our sample, as small teeth of presumed juvenile individuals appear to be gracile versions of their larger (adult) counterparts.

These teeth differ from those of superficially similar Carcharias cuspidatus teeth in our sample by their much smaller overall size, much shorter root lobes, and lack of lateral cusplets. Additionally, teeth of aff. Pseudocarcharias sp. are larger and have a more robust crown, root lobes are more elongated and pointed at their extremities, and a short nutritive groove is limited to the rather thin lingual boss. Alopias sp. teeth are comparatively larger and have broader, more robust crowns.

Probst (1879) originally assigned his new Early Miocene acuarius species to Alopecias , and Cappetta (1970), who identified the species as Aprionodon, illustrated additional specimens (his pl. 17) that provided a more comprehensive overview of heterodonty within the species. Although the species was subsequently synonymized with Isogomphodon (i.e., Bolliger et al. 1995), da Silva Rodrigues-Filho et al. (2023) recently determined that extant Isogomphodon is genetically inseparable from, and should be synonymized with, Carcharhinus , which we follow herein. With their inclusion in Carcharhinus , the various fossil species formerly assigned to Isogomphodon are herein referred to as the daggernose shark species-group within Carcharhinus .

The Catahoula Formation teeth conform in both size range and morphology to C. acuarius . This taxon was apparently widely distributed during the Miocene (see Carrillo-Briceño et al. 2016, 2019; Fialho et al. 2019; Perez 2022; Villafaña et al. 2020). Cicimurri & Ebersole (2021) and Ebersole & Cicimurri (in press) identified Isogomphodon sp. in the lower Oligocene (Rupelian) Rosefield Formation of Louisiana, and comparison of the material they illustrated to the much larger Catahoula Formation sample indicates that the records are conspecific.

The unique body shape of the extant daggernose shark, C. oxyrhynchus (Valenciennes in Müller & Henle, 1839), has been proposed as an adaptation to life within the Amazon River estuary, where conditions are highly turbid ( Compagno 1984). The late Eocene (Priabonian) daggernose shark, Carcharhinus aikenensis ( Cicimurri & Knight, 2019) , and the Catahoula Formation species also apparently preferred a similar environment (see Discussion below).

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.