Ambulocetus.
Ambulocetus natans is a species of early amphibious archaeocete cetacean from the Kuldana Formation in Pakistan during the early Eocene, 48 or 47 million years ago. It is among the most completely known Eocene cetaceans, vital to the study of cetacean evolution and the transition from land to sea. Ambulocetus probably had a long, broad, and powerful snout, and eyes near the top of the head. It may have hunted like a crocodile, waiting near the water's surface and ambushing large mammals, using the jaws to clamp onto and drown or thrash prey. It may have swum like a river otter, alternating beats of the hind limbs while keeping the forelimbs tucked in for most of its propulsive power, simultaneously undulating the torso and tail. It had four functional limbs and may have walked much like a sea lion. It possibly had webbed feet and lacked a tail fluke. It lived in a hot, coastal swamp, probably in a river mouth.
