UPDATE ON THE FIRST UINTA C MICRO-MAMMAL FAUNA FROM THE UINTA BASIN AND ITS COMPARISON WITH A UINTA C MICRO-MAMMAL COMMUNITY FROM LAREDO, TEXAS

A five-ton bulk sample collected during the 2012 field season at micro-mammal locality WU-26 increased the sample volume collected from the site by 33%. Based on more than 50 micro-mammal cheek teeth recovered from the first two tons of 2012 sample, this recent sample will increase the site’s micro-mammal sample size by about 45%. WU-26 is stratigraphically located in the uppermost portion of the Uinta C member of the late middle Eocene Uinta Formation in Uintah County, Utah. The Uinta Formation is the type locality for mammalian specimens which define the Uintan North American Land Mammal age. WU-26 is the first known Uinta C micro-mammal site and provides a unique glimpse into the mammal community which inhabited the Uinta Basin near the end of deposition of the Uinta Formation.

The WU-26 sample size is now large enough to make meaningful comparisons with Uinta C micro-mammal communities outside the Uinta Basin. More than 1000 micro-mammal specimens have been collected at Texas Memorial Museum locality 42486 from the tropical and parallic, late middle Eocene, Laredo Formation, at Laredo, Texas, which is a Uinta C correlate. The two faunas display many similarities at the ordinal level, including having four species of primates. Several genera are present in both faunas including Mytonius, Epihippus, Amynodon, Protoreodon, Mytonomys, Microparamys, and Pauromys, indicating that both environments shared habitats compatible for these taxa. However, it appears that the two communities shared few species as Protoreodon parvus is the only species common to both faunas. That number may grow as the WU-26 sample size increases and genera that have not been identified to species level are better known. It is significant that the earliest known North American lagomorph, Mytonolagus petersoni, is present at WU-26, but absent from 42486.