The mesonychians were a group of mammals that evolved shortly after the K-T extinction. They were small and medium carnivores but eventually the became some of the largest meat-eaters of the Paleogene. They were never very numerous, but because they were related to the ancestors of whales (i.e. Ambulocetus), they are considered to be evolutionary important. The mesonychians looked slightly like modern wolves or hyenas, but they were more closely related to hoofed animals, mostly the even-toed ungulates, like pigs and deer.