Wyoming’s Pass Peak Formation preserves fossils from the Wasatchian, within the Ypresian stage of the Eocene, and records part of the early Eocene world as mammals diversified after the age of dinosaurs. Its finds include several early mammals such as Diacodexis, an early even-toed ungulate, Hyracotherium, an early perissodactyl, and Hyopsodus, as well as the rodent Paramys copei, Diacodon celatus, and indeterminate adapisoricids. These remains place the formation within the Wasatchian and make it an important part of the fossil record used to study early Cenozoic life in Wyoming.