Walking With Whales
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Fossils of Ancient Mammals Explain How Whales Evolved
View a photo gallery of fossilized bones of ancient whales
Illustration of fossilized ankle bones found in Pakistan
Illustration: Copyright Science
Sept. 19, 2001 -- Though whales now populate Earth's oceans, their ancestors once walked upon land. Those are the new findings published in two journals this week, NPR's Joe Palca reports.
These ancient mammals had not just any ankles, Palca reports, but a kind of ankles that are only found in a group of animals known as even-toed ungulates that include sheep, pigs, camels, and hippopotamus. These findings are significant because they finally answer the question of what type of land animals the modern whales evolved from 50 million years ago.
Writing in this week's issue of Nature, Hans Thewissen, a paleontologist at Northeastern Ohio University's College of Medicine, describes how he and his colleagues found a bone that appears to come from a mammal with a head like a whale.
The bone, discovered in Pakistan, was part of the animal's ankle. He writes its unique shape indicates it must have come from ancient ungulates that "looked something like a little deer, maybe around the size of a fox or so." Thewissen says these animals evolved into larger even-toed ungulates, and eventually slipped into the sea.
Fossils of these larger ungulates have also been recently discovered, by another paleontologist Philip Gingerich. As he and his colleagues describe in this week's edition's of Science, at least two sets of skeletons were found near what was the shores of an ancient sea in Pakistan. Gingerich thinks these animals moved around on ground with only a limited capacity despite having an ankle bone. "I think on land they did just about what sea lions do today," he says.
These discoveries confirm the theory by molecular biologists who said, after examining gene inheritance patterns, that whales must be related to the modern even-toed plant-eating ungulates. It was an argument many paleontologists, including Gingerich, found hard to believe.
"It was implausible to us that carnivorous whales would evolve from herbivorous, plant-eating (mammals)" Gingerich says. But he admits he has little choice now. "Well, now we've got the evidence that our molecular colleagues were right, and I think we've solved it."
Visit the official Web site of the American Museum of Natural History to learn more about ancient mammals.