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-Oligocene age fossil specimens from the White River Group in the Buffalo Gap National Grasslands, South Dakota. A skull, preserved within a sandstone concretion that had eroded out of the Scenic Member of the Brule Formation, was discovered within a gully cutting through a slump block. The slump, from the upper part of the Scenic Member, sustained approximately 23 meters of displacement and currently rests upon the upper portion of the underlying Chadron Formation. Slump failure occurred along a slip face with similar orientation to that of the linear stream patterns within the area and both may have the same structural control. The skull lacks most of the cranium (only represented by a sandstone mold), but the maxilla, mandible, some teeth, and part of the right orbital were preserved. After lab preparations at least one of each tooth type is represented, except for the lower incisor (i1). Characteristics used for taxonomic identification were primarily restricted to tooth morphology and positioning. Since the skull was found on a slump with substantial displacement, small mammals from throughout the Scenic Member (Orellan age, NALMA) were considered for identification. The mammalian families under consideration were Agriochoeridae, Camelidae, Hypertragulidae, Leptomerycidae, Merycoidodontidae, and Protoceratidae. Analyses of morphometric characteristics, such as lack of diastema, tooth row lengths, and molar sizes, indicate that the specimen is likely a Merycoidodon starkensis which is part of the Merycoidodontidae family.