Hypanus? heterodontus, Rafinesque, 1818

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 : 54-63

Hypanus? heterodontus sp. nov.

urn:lsid:zoobank.org:act:DECAA150-D2AE-4591-BC8B-2EE90BF5D560

Figs 14–17 , 18A–J

Diagnosis

Low-crowned teeth and high-crowned teeth are represented for this taxon. Low-crowned teeth generally have a convex labial face (amount of convexity varies) with a transversely depressed area near the apex. The labial face bears highly irregular ridges that are weakly to strongly developed and extend onto a wide transverse crest. The lingual face is smooth and bears a medial longitudinal crest flanked by lateral depressed areas. The bilobate root is low, located closer to, and extending beyond, the lingual crown margin. High-crowned teeth are cuspidate, with cusp height and degree of distal and lingual inclination varying. A thin transverse crest subdivides the crown into a large lingual face and much smaller labial face. The labial face may be virtually smooth but is usually ornamented with irregular and disconnected vertical ridges, sometimes forming a reticulated network. The lingual face is smooth and exhibits a medial longitudinal crest of varying width.

New fossil species of Hypanus have yet to be named, but fossil teeth of several extant species (formerly placed in Dasyatis ) have been reported. A small male tooth identified as H. americanus ( Hildebrand & Schroeder, 1928) from the lower Miocene Pungo River Formation of North Carolina has a much more concave labial face and the lingual crown curvature is more pronounced apically than on Hypanus ? heterodontus sp. nov. teeth of similar stature ( Purdy et al. 2001). However, this comparison may be irrelevant, as we believe the Miocene tooth is that of a mobulid ray. Fitch (1966, 1970) reported a total of 12 H. dipterurus ( Jordan & Gilbert, 1880) teeth from Pleistocene deposits of California, but he did not describe or illustrate them. Deynat & Brito (1994) reported caudal spines of H. guttatus ( Bloch & Schneider, 1801) from the Miocene of central South America, but no teeth were noted. Pliocene teeth from the Yorktown Formation of North Carolina identified as H. say ( Lesueur, 1817) by Purdy et al. (2001) are smaller in overall size and more strongly ornamented compared to H.? heterodontus. However, high-crowned teeth of living H. say have a more concave labial face and more strongly lingually curved crown compared to H.? heterodontus, and the ornamentation on low-crowned teeth of the former species does not extend onto the transverse crest as it does on teeth of the latter species (see Reinecke et al. 2023: pls 64–67).

Etymology

The species name refers to the variation in gross crown morphology and ornamentation.

Material examined

Holotype

UNITED STATES OF AMERICA – Mississippi • low-crowned tooth ( Fig. 14P–T ); Catahoula Formation ; SC 2013.28.449 .

Paratypes

UNITED STATES OF AMERICA – Mississippi • high-crowned tooth ( Fig. 14F–J ); Catahoula Formation ; SC 2013.28.406 • high-crowned tooth ( Fig. 14K–O ); Catahoula Formation ; SC 2013.28.409 • low-crowned tooth ( Fig. 14A–E ); Catahoula Formation ; SC 2013.28.444 .

Other material

UNITED STATES OF AMERICA – Mississippi • 574 isolated teeth; Catahoula Formation ; MMNS VP-7530 (16 teeth), MMNS VP-7749 (60 teeth), MMNS VP-7912 , MMNS VP-8742 , MMNS VP-12068 , MMNS VP- 12069 , SC 2013.28.407 ( Fig. 17K–O ), SC 2013.28.408 ( Fig. 16K–O ), SC 2013.28.410 , SC 2013.28.411 , SC 2013.28.412 ( Fig. 16F–J ), SC 2013.28.413 ( Fig. 16P–T ), SC 2013.28.414 to 28.420 , SC 2013.28.421 ( Fig. 17P–T ), SC 2013.28.422 ( Fig. 16U–Y ), SC 2013.28.423 ( Fig. 17U– Y ), SC 2013.28.424 ( Fig. 16A–E ), SC 2013.28.425 to 28.427 , SC 2013.28.428 ( Fig. 16Z –DD), SC 2013.28.431 (19 teeth), SC 2013.28.432 (5 teeth), SC 2013.28.433 (8 teeth), SC 2013.28.434 (5 teeth), SC 2013.28.435 (6 teeth), SC 2013.28.436 (15 teeth), SC 2013.28.437 ( Fig. 15F–J ), SC 2013.28.438 , SC 2013.28.439 , SC 2013.28.440 ( Fig. 15K–O ), SC 2013.28.441 (5 teeth), SC 2013.28.442 (7 teeth), SC 2013.28.443 , SC 2013.28.445 ( Fig. 15P–T ), SC 2013.28.446 (19 teeth), SC 2013.28.447 (15 teeth), SC 2013.28.448 , SC 2013.28.450 ( Fig. 15Z –DD), SC 2013.28.451 to 28.454 , SC 2013.28.455 ( Fig. 15U–Y ), SC 2013.28.456 , SC 2013.28.457 , SC 2013.28.458 (19 teeth), SC 2013.28.459 (22 teeth), SC 2013.28.460 , SC 2013.28.461 ( Fig. 15A–E ), SC 2013.28.462 , SC 2013.28.463 , SC 2013.28.464 (5 teeth), SC 2013.28.465 , SC 2013.28.466 ( Fig. 17A–E ), SC 2013.28.467 (6 teeth), SC 2013.28.468 (11 teeth), SC 2013.28.469 , SC 2013.28.470 ( Fig. 17F–J ), SC 2013.28.471 to 28.473 , SC 2013.28.474 (4 teeth), SC 2013.28.475 ( Fig.18A–E ), SC 2013.28.476 ( Fig. 18F–J ), SC 2013.28.477 (195 teeth) SC 2013.28.478 (55 teeth), SC 2013.28.513 , SC 2013.28.523 (3 teeth), SC 2013.28.524 (5 teeth), SC 2013.28.525 (15 teeth).

Stratum typicum

Shelly, argillaceous sand of the Jones Branch fossil horizon, lower Catahoula Formation, Chattian Stage (horizon no longer accessible).

Locus typicus

Site MS.77.011, Jones Branch, tributary flowing into the Chickasawhay River, south of Waynesboro, Wayne County, Mississippi, USA.

Description

Two morphotypes are represented in the sample, namely low-crowned and high-crowned. Most of the specimens of both morphotypes measure 1.5 mm or less in greatest width (mesio-distal), but a handful of larger specimens (n = 11) measure between 2 mm and 3.2 mm in width.

The low-crowned morphotype has a somewhat six-sided occlusal outline but can appear to be diamond-shaped. The crown width is slightly greater than the length. The mesial and distal ends of the crown are angular (with the angles located somewhat labially), whereas the labial and lingual margins are generally broader and have rounded to straight margins. In labial view, the crown base may be uniformly convex (broadly or narrowly) or can be straight medially (compare Figs 15A, F , 17A ). In profile view, the labial face ranges from weakly to strongly convex, and a weak depression typically occurs within the apical one-half of the crown ( Figs 15E, J , 17E ). The lingual margin may be straight but sloping from the apex to the crown foot ( Fig. 15 DD), but most often it is sub-angular, such that there is a more vertical portion transitioning basally to an elongated heel ( Fig. 17J ). There is a thick transverse crest extending nearly to the crown foot of the mesial and distal sides ( Figs 15H , 17J ). The labial crown face is ornamented to varying degrees, with the ornament ranging from occasional discontinuous and irregular interconnected ridges ( Fig. 15U ) to extensive similar ornamentation forming a reticulated network ( Fig. 15A ). The ornamentation does not reach the base of the crown foot ( Fig. 15A, E ), but it does extend onto the apical surface on the lingual side of the transverse crest ( Fig. 15C, G, M, Q ). The lingual crown face is otherwise smooth. The transverse crest is intersected by a lingual crest that ranges from strong to inconspicuous (compare Fig. 15H to W). In profile view, the crown base is generally straight ( Fig. 15O ), but the labial margin may extend basally beyond the origin of the root ( Fig. 15 DD). In basal view, the enameloid extends to the aboral surface of the crown, and the root appears to emanate from a basin framed by the enameloid ( Figs 15D , 17I ). The bilobate root is large, rather low, and located at the lingual one-half of the tooth ( Figs 15J, Y , 17E ). The root lobes are separated by a wide and deep nutritive groove, and the basal attachment surface is sub-triangular and flat to weakly convex ( Fig. 15I, N ). Well-preserved specimens show that the lobes extend beyond the lingual crown margin ( Fig. 15J ).

The high-crowned specimens measure up to 1.7 mm in crown height, and they have a sub-triangular outline in occlusal view ( Figs 16G , 17L ). In this view, the lingual face is more extensive than the labial face ( Figs 16L , 17Q ). The mesial and distal ends of the crown may be sharply angular or rounded (compare Fig. 16G to AA), and these lateral angles are located closer to the labial margin ( Fig. 16V ). The lingual margin is generally strongly and uniformly convex, but some specimens are embayed laterally. The labial margin ranges from nearly straight to strongly convex (compare Figs 16L and 17V ). In profile view, the labial margin is convex to varying degrees ( Figs 16J , 17T, Y ). The cusp is conspicuous, and on some specimens, it is strongly lingually inclined, such that the labial margin appears to be somewhat angular ( Fig. 17O ). The lingual face is expansive and generally convex, although there are depressed areas on both sides of the crown. The crown foot is extended into a short, straight to sloping shelf-like structure, and the transition from cusp apex to lingual crown foot is strongly concave ( Fig. 16E, Y ). The crown base may be straight, or the labial margin may extend somewhat basally beyond the origin of the root (compare Fig. 16T to 17O). In occlusal (and profile) view, there is a thin transverse crest (close to the labial margin) that extends the entire height of the cusp but does not reach the crown foot ( Fig. 14G, J ). This crest forms the border of the labial face, which itself ranges from very weakly convex to slightly concave (compare Fig. 16U to 17K). Additionally, the labial face is ornamented to varying degrees, ranging from a few incomplete, sinuous vertical ridges ( Fig. 17P ) to more extensive and interconnected ridges ( Fig. 14K ), and sometimes heavy ornamentation consisting of a weakly reticulated network of ridges ( Fig. 17U ). The ornamentation never reaches the crown foot, which is formed by a rim of smooth enameloid ( Fig. 16K, Z ). In labial view, the crown has a sub-triangular outline with the basal margin being uniformly convex to varying degrees (compare Fig. 14K to 16Z) and the cusp being vertical to distally inclined to varying degrees (compare Figs 14F , 16P , and 17P ). Additionally, the mesial and distal sides may be straight ( Fig. 14F ), slightly convex ( Fig. 16F ), concave ( Fig. 17K ), or evenly convex on the mesial side but concave on the distal side ( Fig. 17P ). The transverse crest is intersected on the lingual side by a broad longitudinal crest that does not reach the crown foot ( Figs 14H , 16H , 17M ). In basal view, the enameloid extends to the aboral surface of the crown, and the root emanates from a basin within the enameloid ( Figs 16 CC, 17N). The bilobate root is large and located at the distal one-half of the tooth ( Figs 14O , 16E ). The lobes are separated by a wide and deep nutritive groove, and the basal attachment surface is sub-triangular and flat to weakly convex ( Fig. 16N, S ). Well-preserved specimens show that the lobes extend beyond the lingual crown margin ( Fig. 16O, T ).

Remarks

The low-crowned dasyatid teeth described above are easily distinguished from those of Catahoula Formation rhinopristiform rays (see above) by their roughly six-sided outline, extensive pitted crown ornamentation, lack of lingual lateral protuberances (i.e., uvulae), and the overall morphology of the root. There is extensive morphological variation within our sample of Catahoula Formation dasyatid teeth, which we believe reflects heterodonty within a single species. Extant dasyatid rays exhibit gynandric heterodonty, where female and juvenile male teeth are low-crowned, but teeth of mature males are high-crowned and cuspidate ( Reinecke et al. 2023). The male high-crowned morphology develops during the breeding season, when the pointed teeth are utilized to grasp onto a female during copulation ( Kajiura & Tricas 1996). Although the low- and high-crowned Catahoula Formation morphologies appear to be disparate, the high-crowned teeth bear similar, although much reduced, ornamentation as occurs on low-crowned specimens. Reinecke et al. (2023) provided excellent illustrations of dentitions of numerous extant dasyatid taxa that demonstrate this phenomenon (i.e., compare their pls 70–72, 74), which is also observed in the Catahoula Formation sample we examined. We therefore conclude that the high-crowned morphology represents breeding teeth of mature males, whereas low-crowned teeth represent immature or non-breeding male individuals or females.

With respect to the male cuspidate morphology, there is obvious variation in crown morphology that indicates at least monognathic heterodonty. One specimen ( Fig. 14F–J ) has a tall, broad, and symmetrical cusp that indicates it occupied a file close to the symphysis. Another specimen ( Fig. 17K–O ) has a tall, narrow, and symmetrical crown that may reflect an anterior tooth file. Most specimens have a relatively short and distally inclined cusp, and we believe that they represent lateral tooth files. The tooth height decreases, but cusp inclination increases towards the commissure (compare Figs 16K, P , 17P ). This interpretation is consistent with the morphological variation within extant dasyatid dentitions as shown by Reinecke et al. (2023).

It is also possible that the Catahoula Formation sample reflects dignathic heterodonty. For example, tall and symmetrical cuspidate teeth may have been from the anterior portion of the lower dentition ( Fig. 16K ), but asymmetrical teeth with relatively short cusps may have been from the upper symphyseal region ( Fig. 16U ). With respect to crown width (mesio-distal) versus length (labio-lingual), upper teeth may be broader than their lower jaw counterparts (i.e., compare Fig. 16H to 17L). Low-crowned teeth of extant Hypanus say bearing a transverse apical depression on the labial face occur in the jaws of both male and female individuals (i.e., Reinecke et al. 2023: pls 64–65), so this feature does not provide clarity with respect to distinguishing upper from lower teeth of the Catahoula Formation species. However, crown ornamentation within the upper dentition may be weaker than that of the lower dentition (compare Fig. 15U to A).

The sample of Hypanus? heterodontus sp. nov. available to us includes small and large versions of low-crowned teeth, all of comparable morphology, that we interpret as an ontogenetic increase in tooth size within the new species. Most of the low-crowned teeth measure less than 1.6 mm in greatest width, but some of the largest specimens measure 3.2 mm in this dimension. In occlusal view, these large teeth have a diamond-shaped outline ( Fig. 18A, F ) and in profile view the labial face is convex to varying degrees with an apically depressed area ( Fig. 18D, I ). Additionally, the labial ornamentation of the larger teeth can consist of irregular interconnected ridges like that occurring on small low-crowned teeth (compare Fig. 18B to 15A). Lastly, the crown ornamentation on large teeth extends onto the apical part of the lingual side of the transverse crest ( Fig. 18C, H ). All the features of the large teeth can also be observed on the smaller teeth (i.e., compare Fig. 18A–J to specimens in Fig. 15 ), and we therefore consider the specimens to be conspecific.

The overall crown shapes of the low- and high-crowned teeth, as well as the morphological variation we observed within the Catahoula Formation sample, are consistent with extant Hypanus say as shown by Reinecke et al. (2023). The various forms of heterodonty expressed in H. say also appear to provide the best model with which to compare the Catahoula Formation species. We tentatively assign the new species to Hypanus Rafinesque, 1818 , to indicate close similarities to extant Hypanus teeth and take into consideration the possibility that the extinct species belongs to an unrecognized genus within the Hypanus lineage. Although Hypanus was not included in their study of batoid diversification, Puckridge et al. (2013) indicated that diversification within Dasyatidae began well before the Oligocene. In their recent study of Hypanus diversity, Petean et al. (2024) did not discuss the timing of diversification but recognized three clades within Hypanus . Two of these clades, including the H. americanus and H. say complexes, have representatives living within the present-day Gulf of Mexico ( Hoese & Moore 1998).

Two dasyatid taxa were reported from the Rupelian Ashley Formation of South Carolina by Cicimurri et al. (2022), including “ Taeniurops ” cavernosus ( Probst, 1877) and “ Dasyatis ” sp. The low-crowned morphotype of the former taxon is comparable to the low-crowned teeth from the Catahoula Formation. However, the high-crowned morphology shown by Cicimurri et al. (2022: fig. 7o, u) has more extensive labial ornamentation and a more vertically oriented cusp compared to the Catahoula Formation high-crowned morphotype (compare to Fig. 16J, T ). With respect to low-crowned Miocene teeth assigned to T. cavernosus , these have in common with the Ashley Formation “ T.” cavernosus specimens a deeper apical depression on the labial face that is framed basally by a more conspicuous transverse ridge-like structure (i.e., Cappetta 1970; Villafaña et al. 2020). This morphology is particularly evident on extant T. grabatus ( Geoffroy Saint-Hilaire, 1817) teeth (see Reinecke et al. 2023) and is unlike that of Hypanus ? heterodontus sp. nov. teeth.

Cicimurri & Knight (2009) reported two dasyatid morphotypes from the Chattian Chandler Bridge Formation that are similar to “ Hypanus ” specimens from the Catahoula Formation. Both morphotypes are slightly larger than the Catahoula specimens, and material identified as Dasyatis cavernosa ( Probst, 1877) by Cicimurri & Knight (2009: fig. 8a) has a narrower transverse crest and more extensive labial ornamentation compared to Hypanus ? heterodontus sp. nov. A tooth referred to D. rugosa ( Probst, 1877) by Cicimurri & Knight (2009: fig. 8c) is also comparable to certain Catahoula Formation specimens, but the ornamentation on the South Carolina taxon appears to consist of indistinct rugosities rather than interconnected ridges. Gynandric heterodonty was also documented in the Chandler Bridge sample, as a male tooth attributed to D. cavernosa ( Probst, 1877) by Cicimurri & Knight (2009: fig. 8b) is quite similar to male teeth of Hypanus ? heterodontus from the Catahoula Formation ( Fig. 17K ).

The low-crowned teeth of Hypanus ? heterodontus sp. nov. appear to have a more consistently developed apical labial depression and less organized reticulated ornamentation compared to equivalent teeth from the Oligo-Miocene of Germany identified as Dasyatis delfortriei Cappetta, 1970 ( Reinecke et al. 2005; Haye et al. 2008). The high-crowned (male) teeth of the latter taxon also have a distinctive reticulated labial crown ornamentation compared to similarly shaped teeth of the former taxon (see also Reinecke et al. 2023: text-fig. 1). Low-crowned teeth of the Oligocene Dasyatis rugosa from Germany appear to have a more convex basal portion of the labial face as well as more extensive ornamentation compared to the Catahoula Formation specimens, and high-crowned teeth of the former are also more extensively ornamented compared to Hypanus ? heterodontus ( Haye et al. 2008; Reinecke et al. 2008). Low-crowned teeth of Dasyatis strangulata ( Probst, 1877) from the Oligo-Miocene of Germany ( Reinecke et al. 2008, 2014; also Reinecke & Radwański 2015) lack an apical labial depression, as typically occurs on the Catahoula Formation low-crowned specimens. Additionally, low-crowned teeth of Dasyatis sp. from the Thalberg Beds have more strongly developed crown ornamentation compared to the Catahoula Formation specimens, and the ornamentation on male teeth extends onto the transverse crest of the former but not on the latter ( Reinecke et al. 2014). Low-crowned teeth of T. cavernosus from Miocene strata appear to have a more concave labial face framed by a conspicuous transverse ridge-like structure, a morphology quite obvious on extant Taeniurops grabatus ( Villafaña et al. 2020; Reinecke et al. 2023).

Figures

Fig. 14. Hypanus? heterodontus sp. nov., teeth (type specimens). A–E. SC2013.28.444 (paratype), lowcrowned tooth. A. Labial view. B. Occlusal view. C. Lingual view. D. Basal view. E. Profile view. F–J. SC2013.28.406 (paratype), high-crowned tooth. F. Labial view.G. Occlusal view. H. Lingual view. I. Basal view. J. Profile view. K–O. SC2013.28.409 (paratype), high-crowned tooth. K. Labial view. L. Occlusal view. M. Lingual view. N. Basal view. O. Distal view. P–T. SC2013.28.449 (holotype), low-crowned tooth. P. Labial view. Q. Occlusal view. R. Oro-lingual view. S. Basal view. T. Profile view. Scale bars = 1 mm.

Fig. 15. Hypanus? heterodontus sp. nov., low-crowned teeth. A–E. SC2013.28.461. A. Labial view. B. Occlusal view. C. Lingual view. D. Basal view. E. Profile view. F–J. SC2013.28.437. F. Labial view. G. Occlusal view. H. Lingual view. I. Basal view. J. Profile view. K–O. SC2013.28.440. K. Labial view.L. Occlusal view.M. Lingual view.N. Basal view.O. Profile view. P–T. SC2013.28.445. P. Labial view. Q. Occlusal view. R. Lingual view. S. Basal view. T. Profile view. U–Y. SC2013.28.455. U. Labial view.V. Occlusalview.W. Lingual view.X. Basal view.Y. Profile view.Z–DD. SC2013.28.450. Z. Labial view. AA. Occlusal view. BB. Lingual view. CC. Basal view. DD. Profile view. Scale bars = 1 mm.

Fig. 16. Hypanus? heterodontus sp. nov., high-crowned teeth. A–E. SC 2013.28.424. A. Labial view. B. Occlusal view. C. Lingual view. D. Basal view. E. Profile view. F–J. SC2013.28.412. F. Labial view. G. Occlusal view. H. Lingual view. I. Basal view. J. Profile view. K–O. SC2013.28.408. K. Labial view.L. Occlusal view.M. Lingual view.N. Basal view.O. Profile view. P–T. SC2013.28.413. P. Labial view. Q. Occlusal view. R. Lingual view. S. Basal view. T. Profile view. U–Y. SC2013.28.422. U. Labial view.V. Occlusalview.W. Lingual view.X. Basal view.Y. Profile view.Z–DD. SC2013.28.428. Z. Labial view. AA. Occlusal view. BB. Lingual view. CC. Basal view. DD. Profile view. Scale bars = 1 mm.

Fig. 17. Hypanus? heterodontus sp. nov., teeth. A–E. SC2013.28.466, low-crowned tooth. A. Labial view. B. Occlusal view. C. Lingual view. D. Basal view. E. Profile view. F–J. SC2013.28.470, lowcrowned tooth. F. Labial view. G. Occlusal view. H. Lingual view. I. Basal view. J. Profile view. K–O. SC2013.28.407, high-crowned tooth. K. Labial view. L. Occlusal view. M. Lingual view. N. Basal view. O. Profile view. P–T. SC2013.28.421, high-crowned tooth. P. Labial view. Q. Occlusal view. R. Lingual view. S. Basal view. T. Profile view. U–Y. SC2013.28.423, high-crowned tooth. U. Labial view. V. Occlusal view. W. Lingual view. X. Basal view. Y. Profile view. Scale bars = 1 mm.

Fig. 18. Hypanus? heterodontus sp. nov. (A–J) and Dasyatidae gen. et sp. indet. (K–T), teeth. A–E. SC2013.28.475, Hypanus? heterodontus, tooth. A. Occlusal view. B. Labial view. C. Lingual view. D. Profile view. E. Basal view. F–J. SC2013.28.470, Hypanus? heterodontus, tooth. F. Occlusal view. G. Labial view. H. Lingual view. I. Profile view. J. Basal view. K–O. SC2013.28.429, Dasyatidae gen. et sp. indet., tooth. K. Occlusal view. L. Labial view. M. Lingual view. N. Profile view. O. Basal view. P–T. SC2013.28.430, Dasyatidae gen. et sp. indet., tooth. P. Occlusal view. Q. Labial view. R. Oro-lingual view. S. Profile view. T. Basal view. Scale bars = 2 mm.