Systematics of the late Eocene 'oreonetine' oreodonts (Merycoidodontidae: Artiodactyla).

The small, primitive 'oreonetine' oreodonts from the late Eocene (Chadronian) of North America have long been a systematic mess with gross oversplitting, failure to recognise post-mortem distortion of specimens and many errors in their descriptions. We describe some new fossils and review the group for the first time since 1956. Of the six genera and nine species recognised by Schultz & Falkenbach (1956), only three genera (Oreonetes, Limnenetes, and Bathygenys) and six species are now considered valid. The 'Oreonetinae' is a paraphyletic wastebasket group because some members are closer to more derived oreodonts than others, and Limnenetes is a primitive leptauchenine, not a merycoidodontine. These small, rare late Eocene oreodonts found only in Wyoming, Montana, and Texas are the precursors to the enormous radiation of oreodonts in the early Oligocene. [ABSTRACT FROM AUTHOR]