Pakicetus is widely recognized as an early four-legged ancestor in the evolution of whales.
Pakicetus lived roughly 50 million years ago during the early Eocene. Fossils discovered in what is now Pakistan show an animal with a terrestrial, wolf-sized body, while details of its skull and ear region link it to the cetacean lineage. It was not a modern whale and probably lived mainly on land near water.
Whale evolution is documented by a sequence of fossils showing major anatomical changes. Later forms such as Ambulocetus had limbs suited to movement in water and on land, while fully aquatic relatives gradually developed tail-powered swimming, modified forelimbs, and reduced hind limbs.
Pakicetus belongs to the artiodactyl branch of mammals, the group that also includes hippos. Its fossils helped overturn the older view that whales had no close relationship with hoofed mammals.