Variability of dental morphology and the relationships of the earliest arctocyonid species

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Abstract
This study focuses on the variability of dental morphology and the relationships of the earliest arctocyonid species. Analysis of arctocyonid premolars and molars from the Bug Creek Anthills local fauna (Hell Creek Fm., Puercan, Montana) shows far wider ranges of variation of many dental characters than were previously recognized. Based on morphological and morphometrical differences, two additional species, Oxyprimus erikseni and Mimatuta morgoth, are distinguished from Protungulatum donnae within the arctocyonid sample from the Bug Creek Anthills local fauna. Cladistic analysis of 18 dental characters of O. erikseni, P. donnae, M. morgoth and the Late Cretaceous eutherian outgroup taxa suggests that P. donnae and M. morgoth form a monophyletic group to the exclusion of O. erikseni. New data suggest that it is necessary to modify the stratigraphic ranges of these arctocyonid species. In order to ensure the reliability of the biochronological sequence of the Bug Creek channel deposits based on the number of arctocyonid species, it is also necessary to further assess the ranges of dental variations of arctocyonids with larger samples of specimens from other Bug Creek channel deposits in addition to Bug Creek Anthills.