An investigation and comparison of latest Eocene (Chadronian) mammalian faunas found in the intermontane basins and plains of Colorado

The Eocene-Oligocene transition has been considered by some as "the most significant event in earth history since the extinction of dinosaurs". During this transition period, the climate significantly cooled and was accompanied by an increase in the mean annual range of temperature. Changes in floral and faunal compositions during this period have been well documented in the western states of North America, but there has been little investigation into the changes in faunal composition along an altitudinal gradient at the end of the Eocene. Here I investigate the latest Eocene (Chadronian NALMA) mammalian fauna of six assemblages in Colorado. I update the mammalian faunal list of the Florissant Formation, and also report the first mammalian faunal list for the White River Formation in Kings Canyon, North Park Basin, Colorado. The mammalian fauna corroborates the Chadronian (latest Eocene) age determined by others.