Re-evaluating hypertragulid diversity in the John Day basin, Oregon, USA
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Date
2024-09-25
Authors
Famoso, Nicholas
Jewell, Lana K.
Journal Title
Journal ISSN
Volume Title
Publisher
Acta Palaeontologica Polonica
Abstract
Despite their relative abundance, members of the family Hypertragulidae (Artiodactyla, Mammalia) have proved a conundrum regarding species diversity in the Turtle Cove Member (Oligocene) of the John Day Formation, located in central and eastern Oregon. Three species and two separate genera are described in the area, but previous research lacks statistical support for this level of variation. We use coefficients of variation (V) on measurements of dentition and astragali of hypertragulid specimens designated Hypertragulus hesperius, Hypertragulus minutus, and Nanotragulus planiceps as a metric for determining whether there were multiple species present in the population. Asymptotic and modified signed-likelihood ratio V equality tests show that V values of anterior-posterior molar length and transverse molar width vary significantly when comparing single species of modern ecological analogs (Muntiacus muntjak, Muntiacus reevesi, and Tragulus javanicus) to groupings of a combined population. However, the V equality tests on dental and postcranial measurements yield almost no significant results when comparing variation in the extinct John Day hypertragulids to an extant population comprised of a single species. Similar comparisons between astragali measurements of hypertragulids and T. javanicus express no significant difference in the level of variation from the combined population to a modern single species. The low level of variation in the hypertragulids and the lack of differentiation between dental characters of individuals does not statistically support the hypothesis that there were multiple species present in the population, suggesting either that cryptic species may be present but impossible to identify without soft tissue remains, or there may have been taxonomic over-splitting of a single hypertragulid species in the John Day region.
Description
13 pages
Keywords
Mammalia, Artiodactyla, Hypertragulidae, morphometrics, dental morphology, astragalus, coefficient of variation, John Day Formation