SPECIES DIVERSITY IN THE HYPERTRAGULID (MAMMALIA: ARTIODACTYLA) POPULATION OF THE JOHN DAY BASIN, OREGON

Members of the family Hypertragulidae (order Artiodactyla, class Mammalia) are the most abundant mammals in the Turtle Cove Member (Oligocene) of the John Day Formation of central and eastern Oregon and make up a significant portion of the preserved specimens of the John Day Basin. While three species of hypertragulids have been described in the John Day Basin, no prior statistical analysis of variation in the John Day population to determine if this specific division is in fact accurate have been conducted. The most commonly used method for determining species among artiodactyls is examination of dental characters, both morphology and measurement. However, research conducted with modern artiodactyls has called into question the validity of dentition as a faultless diagnostic technique—populations of artiodactyls experience such uneven wear on their teeth that there is greater than average variation in dental measurements. Recently, there has been increased interest in the possibility of postcranial characters as a diagnostic on fine taxonomic scales. While this has not yet been successful in all families, there is potential that astragali could function as a second diagnostic character to support the primary analysis of dentition in Hypertragulidae. We are using coefficients of variation (V) on dental measurements and astragali measurements of hypertragulid specimens designated Hypertragulus hesperius, Hypertragulus minutus, and Nanotragulus planiceps as a metric for determining if there is more than one species present in the population. Preliminary results show no statistical difference in coefficients of variation of anterior-posterior length (APL) or transverse width (TW) of molars in the John Day population as compared to a modern population of Muntiacus muntjak. However, modified signed-likelihood ratio test comparison amongst APL and TW identified species of hypertragulids as significantly different from each other. While we hope to confirm these results with a similar analysis of astragali, there is a lack of statistical support for three species of hypertragulids in the John Day Basin.