Wyoming’s Evanston Formation preserves rock layers from the Late Cretaceous through the Paleocene, making it an important record of a major transition in Earth’s history. Its fossils capture both the end of the age of dinosaurs and the mammal faunas that followed. Dinosaur remains found there include Triceratops horridus and Alamosaurus, while Paleocene fossils include multituberculates, primates, condylarths, creodonts, and insectivores. Together, these finds make the formation significant in paleontology for showing life across the boundary between late dinosaur ecosystems and the early age of mammals.