Ancestors of modern-day whales, such as Pakicetus, were amphibious cetaceans and possessed legs. Ambulocetus, a descendant of Pakicetus, had shorter legs more suited for aquatic life in addition to paddle-shaped feet.
Ambulocetus lived approximately 50 to 48 million years ago near bodies of both fresh and salt water in Pakistan. It is believed that it hunted prey in a similar manner to crocodiles, wading in shallow waters before ambushing. Ambulocetus grew to a length of 10 feet and most likely swam by undulating its back. Its ability to swallow while underwater and the structure of its periotic bones are direct links to later-appearing whales.