for National Geographic News
The nearest ancestors of Earth's largest-ever animals were tiny deerlike creatures that jumped into rivers to flee prehistoric predators, a new study suggests.
These semiaquatic, raccoon-size mammals dubbed Indohyus lived in southern Asia some 48 million years ago. (See more pictures of the possible whale ancestor.)
Indohyus is part of a large group of mammals known as artiodactyls, which includes pigs, sheep, hippos, and giraffes.
Several recent fossil studies suggest that artiodactyls gave rise to whales, and that the hippopotamus is their closest living relative.
But hippos don't appear in the fossil record until about 35 million years after whales diverged from their land-dwelling ancestors, leaving a gap in the evolutionary chain.
For the new study, a team led by paleontologist Hans Thewissen examined hundreds of Indohyus fossils found in mudstone in Indian-controlled Kashmir.
"We think that Indohyus was living there in little herds and that a whole bunch of these animals died," said Thewissen, of Northeastern Ohio Universities Colleges of Medicine and Pharmacy.
"Their bones were then washed into this river and they were all buried together."
The fossils show distinct features that suggest the ancient ungulates, or hoofed mammals, are the long-sought "missing links" in the evolution of whales, the scientists report in tomorrow's issue of the journal Nature.
In particular, the structure of the animal's skull and ears show that Indohyus was closely related to whales, the study team said.
These findings were "very surprising," given Indohyus' deerlike appearance, Thewissen said.
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