New insights on the most primitive desmostylian from a partial skeleton of Behemotops (Desmostylia, Mammalia) from Vancouver Island, British Columbia

ABSTRACT

A partial articulated skeleton of a desmostylian was found in siltstone of the Sooke Formation in the streambed at the mouth of the Sombrio River in Juan De Fuca Provincial Park, Vancouver Island, British Columbia, Canada. Another exposure of the Sooke Formation southeast of the locality has been dated to Chron C6Cr age, 24.1–24.8 Ma. This specimen includes the left side of the skull, two molars, a premolar, canines, partial scapula, nearly complete humerus, and numerous vertebrae and ribs. Molar characteristics are the same as material of Behemotops proteus from the Pysht Formation of Washington State, which is near the type locality of Behemotops proteus of the upper Oligocene Pysht Formation, Washington State. Previous specimens of B. proteus were limited to lower jaws and portions of the upper and lower postcanine dentitions. The slightly smaller Behemotops katsuiei from Japan is known from more elements, yet its cranial material is limited to the posterior portion of the cranium and a small portion of the zygomatic arch. This new material allows us to see that Behemotops cf. B. proteus had cranial features much like those seen in Cornwallius sookensis of North America. These include a postorbital process of the jugal, with the zygomatic process of the squamosal not dorsally expanded, a concave hard palate, enlarged canine tusks that point ventrally, and a narrow, curved incisor arcade on a narrow rostrum. This is different from specimens previously referred to as Behemotops emlongi and then synonymized with B. proteus, which have a broad symphysis with large tusks. These specimens formerly known as B. emlongi are now referred to a new genus.

http://zoobank.org/urn:lsid:zoobank.org:pub:A528C91D-8ED7-4A7E-BBF2-82BA296D10E4

Acknowledgments

We would like to thank J. Kerik (RBCM) for her assistance with and curation of this specimen. We thank J. Kerik and R. Hebda (RBCM) and D. Bohaska and R. Purdy (USNM) for assistance with collections in their care, and fruitful discussions about these faunas. We thank J. Goedert and M. Johns for their assistance and comments on geological context. We would especially like to thank G. Hanke (RBCM) for his careful collection of most of the material in July 2007, and Dr. V. Saly, Dr. J. Hostetler, A. Wyngaards, and C. Wright for their effort in calling the initial finds to the attention of RBCM staff. Without these informed eyes and considerate actions, none of this would be possible.

Handling editor: Erich Fitzgerald.

Citation for this article: Beatty, B. L., and T. C. Cockburn. 2015. New insights on the most primitive desmostylian from a partial skeleton of Behemotops (Desmostylia, Mammalia) from Vancouver Island, British Columbia. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.979939.