Hypanus heterodontus Rafinesque 1818
Year: 2025
Type: other
Abstract: 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 broa
Language: English
Subfield: Paleontology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W6912085831
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