'A group of researchers says that the closest known evolutionary cousin of whales, dolphins and porpoises is not the hippopotamus, as conventional wisdom has it, but an extinct deer-like animal roughly the size of a raccoon. In a new study, the team finds that a fossilized specimen of the extinct, 48-million-year-old mammal Indohyus bears several telling similarities to whales, including dense limb bones for ballast and a middle ear structure found only in the cetaceans, or sea-dwelling mammals, which is thought to help them hear underwater.
'"What we think happened is that the ancestors of both Indohyus and whales were animals that looked like a tiny deer," says Hans Thewissen, professor of anatomy at Northeastern Ohio Universities Colleges of Medicine and Pharmacy, who led the study, published in Nature. The modern creature that most resembles Indohyus, however, is the African mousedeer (or chevrotain), which lives on the forest floor but scurries into the water to take cover from predators [see video of eagle pursuing chevrotain]. Similarly, Thewissen says, the common ancestor of whales and Indohyus may have been a herbivore (plant-eaters) that took to water to hide out, but eventually switched to a swimming, meat-eating lifestyle, which it passed down to modern cetaceans.' (Scientific American article).
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