Rhombodus is one of two genera, from the Upper Cretaceous of Europe, the Near East, Africa and the Americas, that make-up the extinct family Rhombodontidae. The family is only known from its rhombic teeth (and caudal spines), that would have made-up a rhinopterid-like tooth-plate. Unlike the multi-lobed (polyaulacorhizous) teeth of the rhinopterids and myliobatids, rhombodontid teeth are bilobate (holaulacorhizous). Cappetta (1987: 174-75) describes the teeth as appearing rhombic (occasionally hexagonal) occlusally with vertical wrinkles on the labial and lingual faces and reaching 1.8 cm in width. Scattered foramina reside in a deep nutrient groove that separates triangular root lobes.
Teeth attributed to R. levis CAPPETTA & CASE 1975 are common in the Late Cretaceous of New Jersey and North Carolina. Most collected teeth have very low crowns (feeding-wear). However, sufficient fossil specimens have high-crowns to speculate that the teeth of this dentition were not, at least strongly, interlocked. Unlike tooth illustrations of other members of the genus, the labial and lingual faces of R. levis are relatively smooth and do not appear to have the strong apico-basal enameloid ridges (wrinkles) that characterize the teeth of this genus. However, traces of broad low ridges can be seen near the base of the crown.
Cappetta (1987: 175) lists the various species as being from the Maastrichtian except the oldest representative, R. levis, which is Upper Campanian (Mt Laurel Sands, New Jersey). Schwimmer,(1986: 115) reported this design from the Campanian of Georgia and these teeth are present in North Carolina as well (pers. obs.).
It has been argued (Earl Manning, pers. comm., 2007; Manning, 2006, pp. 228-9) that the tooth-design described as "Rhombodus levis" might not belong to Rhombodus at all, but represent reduced lateral tooth-positions (rhinopterid-like) of Brachyrhizodus wichitaensis, which he interprets as a primitive myliobatid. Lacking sufficient B. wichitaensis specimens to validate this hypothesis, I present it as an alternate viewpoint; given enough material from a single locale and horizon, this should be quite provable if correct.
A Maastrichtian taxon, Case (1979) includes R. binkhorsti DAMES 1881 in the Peedee fauna of North Carolina and Welton and Farish (1993: 155) in Texas. Manning (2006, pp. 320-321) records R. binkhorsti from the Maastrichtian. of Mississippi, Tennesse and Alabama. They refer to its teeth, which reach 10 mm in width, as having a roughly rhombic crown with numerous vertical folded and wrinkled enameloid ridges. Cappetta (1987: 175) notes that the distribution of this species is similar to the genus. Case & Cappetta (1997: 154. plate 8.3) included as Rhombodus ? sp teeth with higher but narrower roots; the authors were unsure if this was merely a variation of the binkhorsti-design or a different species (note in Figure that the roots lack the triangular basal profile and that they appear splayed).
Cappetta, H., 1987. Chondrichthyes II. Mesozoic and Cenozoic Elasmobranchii. In: Handbook of Paleoichthyologie, vol. 3b, Gustav Fischer Verleg, Stuttgart, 193 pp.
Cappetta, H., 2006.. Elasmobranchii post-Triadici (index generum et specierum). In: Riegraf, W. (Ed) Fossilium Catalogus I:Animalia 142. Leiden, Backhuys Publish, 472pp.
Cappetta, H. & Case, G., 1975. Contribution ŕ l'étude des sélaciens du groupe Monmouth (Campanien - Maestrichtian) du New Jersey. Palaeontographica Abteilung A, 151:1-46.
Case, G., 1979. Cretaceous Selachians from the Peedee Formation (Late Maestrichtian) of Duplin County, North Carolina, Brimleyana, Vol 2, pp 77-89.
Case, G., and H. Cappetta. 1997. A new selachian fauna from the late Maastrichtian of Texas. Muünchener Geowissenschaften Abhandungen 34:131-189.
Manning, E., 2006. Late Campanian vertebrate fauna of the Frankstown site, Prentiss County, Mississippi; systematics, paleoecology, taphonomy, sequence stratigraphy. Unpub. PhD dissertation, Tulane Univ., New Orleans, xvii+419 p., 16 pls.
Schwimmer, D., 1986. Late Cretaceous fossils from the Blufftown Formation (Campanian) in western Georgia. The Mosasaur, III:109-119.
Welton, B. and Farish, R., 1993. The Collector's Guide to Fossil Sharks and Rays from the Cretaceous of Texas. Before Time, Texas. 204 pp.