254 Proceedings of the South Dakota Academy of Science, Vol. 89 (2010) A NEW STRATIGRAPHIC OCCURRENCE OF THE LEPTAUCHENIINE OREODONT SESPIA IN THE UPPER BRULE FORMATION OF SOUTH DAKOTA E. Welsh Department of Geology and Geological Sciences South Dakota School of Mines and Technology Rapid City, SD 57701 [email protected] ABSTRACT Fossil collecting in the White River Group has been done for over 150 years, yielding limited new information on the fossil fauna. A new find out of an old discovery, however, provided an opportunity to re-examine specimens that had been overlooked. The Museum of Geology at SDSM&T has a skull of Leptauchenia (Sespia) nitida that had been on display since the 1932. What is interesting about this particular specimen is the recorded stratigraphic location which expands the genus Sespia from the Sharps Formation to the Upper Brule Formation in South Dakota. This stratigraphic unit is known to contain fauna from the Whitneyan North American Land Mammal Age, but not Sespia. Measurements taken under the convention of previous researchers and mor- phological characters of the skull were used to validate the integrity of the initial identification. Resulting data were compared to previously identified species and type specimens, which were used as taxonomic anchors. This study shows that this specimen was correctly identified as Sepsia nitida. The lithology of the remaining matrix on the specimen was utilized to verify its geologic origin based on the recorded locality. The matrix secured to the skull is siltstone comparable to the Whitney member of the Brule Formation, as seen in Nebraska, which is close to the approximate physical location of the site where the specimen was collected. This new information from a skull collected about eighty years ago is providing new insights on the Oreodont subfamily Leptaucheniinae..