Forty-five million years ago, an 8-foot-long (2 meters), 500-pound (227 kilograms) beast called Rodhocetus kasrani waddled into the water and dove, using webbed hoofs to paddle speedily out to the open sea like some nightmarish cross between a crocodile and a shark.
When orcas and dolphins catch fish, they like to swallow them whole. Their little peg-like teeth are just there to grip their prey long enough to get it down their gullets. Not so with Rodhocetus kasrani, who sported a diverse mouthful of fangs, slicers and grinders for shearing its victims into easy-to-swallow morsels. Also unlike orcas and dolphins, R. kasrani had enough legginess to locomote on land whenever that seemed like a good idea.
Different as they are from modern whales, these early cetaceans had all kinds of whale-ish traits, including something in their jaw inelegantly named a "mandibular fat pad." When we Homo sapiens dive underwater, what little sound we can hear is transmitted as vibrations in our skulls, giving us no sense of the source's location. A whale's handy fat pad aids in directional hearing — allowing predators like the gruesome Rodhocetus kasrani to get an instant fix on the whereabouts of its next meal [source: Gingerich et al.].