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 about 40% of the preserved specimens of the John Day Basin. Three species and two separate genera are described in the area, but any preexisting research lacks statistical support for this level of variation. Species designation among extinct artiodactyls is predominantly based on morphological and morphometric examination of dentition, but studies conducted with extant artiodactyls have revealed that this may not be a reliable diagnostic technique. Other research introduces the possibility of postcranial morphology as indicative of species, but this is not successful in all artiodactyl families. Given these two possible metrics, I used 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. Both the asymptotic V equality test and the modified signed-likelihood ratio V equality test show that V values of anterior-posterior molar length (APL) and transverse molar width (TW) vary significantly when comparing single species of modern ecological analogs (Muntiacus muntjak, Muntiacus reevesi, and Tragulus javanicus) to groupings at the genus level. However, the V equality tests on dental and postcranial measurements yield almost no significant results when comparing variation in the extinct John Day hypertragulid population to an extant population comprised of a single species. The low level of variation in the hypertragulids statistically supports the hypothesis that there is only one species present in the population, which suggests over-splitting of the species in the John Day Basin