Mesonychia is an extinct order of small to large-sized omnivorous to carnivorous hoofed mammals related to ungulates. Originally, it was hypothesized that mesonychians were a group of ungulates, however recent analysis now found them to be outside of the group entirely. Instead were a basal order of hoofed mammals within Pan-Euungulata. Mesonychians first appeared in fossil record in the Early Paleocene of East Asia with Dissacus rotundus, Yantanglestes, Hukotherium, and Dissaccussium. However, it believed that mesonychians evolved during the Late Cretaceous, at least 66.7 Ma.