Myledaphus bipartitus was erected by Cope (1876) for a tooth-design common in the Judith River Fm (Campanian) of Montana. These teeth were generally deemed to be freshwater stingrays until Cappetta (1987:140-41) judged them ; Cappetta's conclusion was validated (he's so damn good) when in 1999 a complete skeleton was found in Alberta (Neuman & Brinkman, 2005:168). Based on reported locations and tooth-design, Myledaphus bipartitus was likely a fresh / brackish water taxon with a crushing dentition feeding on invertebrates.

The crowns are high, usually hexagonal and broader than deep; the occlusal surface bear a transverse ridge with apico-basal folds extending down the labial & lingual faces. The roots are high with a nutrient groove separating rather triangular lobes with multiple small foramina; the marginal root face has scattered foramina near the crown with a larger one lingually. Cappetta (1987: 140-41) noted that they are up to 7 mm wide and a second nutrient groove may be present.

Reports of this taxon are largely confined to the Late Cretaceous of the Western Interior Seaway (New Mexico & Utah to Alberta and Saskatchewan); but as Cappetta (1987) noted, they are also known the Late Cretaceous of Uzbekistan (Nessov 1981) and Lower Paleogene of NA (which he questioned).

At least one other unnammed Myledaphus-like tooth-design appears to be present in the Western Interior Seaway and/or Gulf Coast.

  • Meyer (1974: 158-59, fig. 49) included as ?Hypolophus sp. a Campanian tooth-design from Mississippi with a high rhombic crown and high roots, similar to design of Figures and below.
  • Peng et al (2001: 8-10) in reporting on the Judith River Group (Milk River & Foremost Fms., Campanian) of Alberta, included the typical M. bipartitus tooth as such (pl.2, figs. 1-3), but included a specimen which appears to be a cross between Pseudohypolophus and Myledaphus as Myledaphus sp (pl2, fig 4-6).
  • In two GSA poster abstracts, Thompson (2004 & 05) discussed two distinct Myledaphus tooth-designs from Utah; one Santonian (blocky, less-deep crown) and the other Campanian (rounder, core bulbous crown). Lacking figures, it will be interesting to see final determinations if this research is ever published.
  • Bourdon et al (2011) reported from the Pt. Lookout Fm. (E-M Santonian) of New Mexico Myledaphus sp. and noted the similarity to M. bipartitus but the lack of vertical folds of the crown face and no evidence of a transverse ridge.

    Selected References

    Acorn, J., 2007. Deep Alberta. University of Alberta Press. 186 pp
    Becker, M.A., Chamberlain, J.A., jr., and Terry, D.O., 2004. Chondrichthyans from the Fairpoint Member of the Fox Hills Formation (Maastrichtian), Meade County, South Dakota. Journal of Vertebrate Paleontology, 24:780–793.
    Bourdon, J., Wright, K., Lucas, S.G., Spielmann, J.A. and Pence, R., 2011. Selachians from the Upper Cretaceous (Santonian) Hosta Tongue of the Point Lookout Sandstone, central New Mexico. New Mex. Mus. Nat. His. and Sc., Bulletin 52; 54pp.
    Cappetta, H., 1987. Chondrichthyes II. Mesozoic and Cenozoic Elasmobranchii. In: Handbook of Paleoichthyologie, vol. 3b, Gustav Fischer Verleg, Stuttgart, 193 pp.
    Case, G., 1978. A new selachian fauna from the Judith River Formation (Campanian) of Montana. Palaeontographica (A), 160:176-205.
    Cope, E., 1876. Description of some vertebrate remains from the Fort Union beds of Montana. Proceedings of the Academy of Natural Sciences of Philadelphia, XX, 248-261.
    Estes, R. 1964. Fossil vertebrates from the Late Cretaceous Lance Formation, eastern Wyoming. University of California publications in the Geological Sciences 49: 1- 180.
    Hoganson, J. and E. Murphy, 2002. Marine Breien Member (Maastrichtian) of the Hell Creek Formation in North Dakota: Stratigrpahy, vertebrate record, and age. In, eds: J. Hartman, K. Johnson, & D. Nichols. The Hell Creek Formation and the Cretaceous -Tertiary Boundary in the Northern Great Plains: An integrated continental record of the end of the Cretaceous. Geo. Soc. of Amer. - Special Paper 361; pp 247-270.
    Hussakof, L., 1908. Catalogue of types and figured specimens of fossil vertebrates in the American Museum of Natural History. Pr. 1 - Fishes. Bulletin of the AMNH, 25:1-104, 6 pls.
    Nessov, L., 1981 Cretaceous salamanders and frogs of Kizylkum Desert. Akad. Nauk. SSSR, 101, p 57-88.
    Neuman, A and D. Brinkman, 2005. Fishes of the Fluvial Beds. In, eds: Currie, P. & Koppelhus, E. Dinosaur Provincial Park - A Spectacular Ancient Ecosystem Revealed. Indiana Univ. Press. pp 167-185.
    Peng, J., A. Russell and D. Brinkman, 2001. Vertebrate Microsite Assemblages (exclusive of Mammals) from the Foremost and Oldman Formations of the Judith River Group (Campanian) of southeastern Alberta: an illustated guide. Prov. Mus of Alberta, Occasional Paper 25, 54pp.
    Thompson, C., 2004. A preliminary report on biostratigraphy of Cretaceous freshwater rays, Wahweap Formation and John Henry Member of the Straight Cliffs Formation, southern Utah. GSA Abstracts with Programs, Vol. 36, No. 4, p. 91.
    Thompson, C., 2005. Biostratigraphic utility of Santonian-Campanian (Late Cretaceous) nonmarine ray (Rhinobatoidea) teeth, southern Utah. GSA Abstracts with Programs, Vol. 37, No. 6, p. 9.

     

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