A new middle Paleocene mammalian fauna from the Fort Union Formation, Great Divide Basin, Wyoming.

摘要

Mammalian faunas that span the Torrejonian-Tiffanian boundary have been reported by others from the Hanna and Bighorn Basins, and are important for assessing mammalian diversity and evolution during middle Paleocene time. Here, we report a Torrejonian - Tiffanian transitional fauna from the Overland Member of the Fort Union Formation in the Great Divide Basin, south-central Wyoming. The fauna, which is primarily comprised of isolated teeth, includes 20 species in five mammalian orders.;The Overland fauna is similar to latest Torrejonian faunal assemblages; however, it also contains the plesiadapid Nannodectes intermedius, an index taxon for the earliest Tiffanian, and Ectocion, which first appears in Ti1 as well. Based upon presence of N. intermedius and Ectocion, as well as similarities to earliest Tiffanian fauna in the Hanna Basin, the faunal assemblage suggests the Overland Member is earliest Tiffanian (Ti1) in age.