Pakicetus is an extinct genus of amphibious cetacean of the familyPakicetidae, which was endemic to Pakistan during the Eocene, about 50 million years ago. It was an animal rather like a wolf, about 1 metre (3 ft 3 in) to 2 metres (6 ft 7 in) long, and lived in and around water where it ate fish and small animals. The vast majority of paleontologists regard it as the most basal whale, representing a transitional stage between land mammals and whales. It belongs to the even-toed ungulates with the closest living non-cetacean relative being the hippopotamus.
Based on the skull sizes of specimens, and to a lesser extent on composite skeletons, species of Pakicetus are thought to have been 1 metre (3 ft 3 in) to 2 metres (6 ft 7 in) in length.
Pakicetus looked very different from modern cetaceans, and its body shape more resembled those of land-dwelling hoofed mammals. Unlike all later cetaceans, it had four fully functional long legs. Pakicetus had a long snout; a typical complement of teeth that included incisors, canines, premolars, and molars; a distinct and flexible neck; and a very long and robust tail. As in most land mammals, the nose was at the tip of the snout.
Reconstructions of pakicetids that followed the discovery of composite skeletons often depicted them with fur; however, given their relatively close relationships with hippos, they may have had sparse body hair.
The first fossil found consisted of an incomplete skull with a skull cap and a broken mandible with some teeth. Based on the detail of the teeth, the molars suggest that the animal could rend and tear flesh. Wear, in the form of scrapes on the molars, indicated that Pakicetus ground its teeth as it chewed its food. Because of the tooth wear, Pakicetus is thought to have eaten fish and small animals. The teeth also suggest that Pakicetus had herbivorous and omnivorous ancestors.