Abstract

Uintasoricines are diminutive plesiadapiforms that are found in the latest Paleocene through middle Eocene, predominantly in North America. They are not a diverse group but individual species may be locally abundant and they are a persistent element of the plesiadapiform radiation in North America surviving over a span of approximately 16 million years. Recent field work in southern Wyoming at South Pass has led to the discovery of a new genus and species of uintasoricine. The new form is smaller in tooth dimensions compared to other known uintasoricines, being slightly smaller than Uintasorex montezumicus from California. Both the newly described taxon and U. montezumicus are among the smallest plesiadapiforms yet known with body weights estimated to be 20 to 25 g. The sediments of the Cathedral Bluffs Tongue of the Wasatch Formation at South Pass contain a unique upland fauna—the presence of a distinctive uintasoricine in this assemblage adds further evidence to support the notion that this upland environment was a biodiversity hotspot during the latest early Eocene.

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