A TAXONOMIC AND GEOLOGIC STUDY ON AN OREODONT SKULL EXCAVATED FROM BUFFALO GAP NATIONAL GRASSLANDS OF SOUTH DAKOTA

During the summer of 2012, a Wayland Baptist University geology field team located and excavated numerous Eocene age fossil specimens from the White River Group in the Buffalo Gap National Grasslands, South Dakota. One of the specimens collected from the Scenic Member of the Brule Formation was a skull which was field identified as an Oreodont. The skull was preserved within a sandstone concretion that had eroded from the Scenic into a gully cut in a slump block. The slump, composed of the Scenic Member, sustained approximately 23 meters of displacement and is currently resting within the upper portion of the underlying Chadron Formation. Most of the specimen’s cranium was not present, being represented by a sandstone mold, but the actual maxilla, mandible, and part of the right orbital were preserved. After lab preparations it was revealed that at least one of each tooth type is represented, although not all teeth are present. Morphometric comparisons were therefore primarily restricted to tooth morphology and positioning, which gave clear indications of mammalian origins. Since the skull was found on a slump with substantial displacement, mammals from throughout the lower Brule (Orellan age, NALMA) had to be considered as possible candidates during the identification process. The Mammalian families under consideration were Merycoidodontidae, Agriochoeridae, Camelidae, Xiphodontidae, Protoceratidae, and Leptomerycidae. After comparisons of dental morphologies, it was concluded that the fossil skull belonged to the Merycoidodontidae family, a type of Oreodont. Further analysis is underway to better define the taxonomic position of the specimen.