for National Geographic News
An early whale had large back legs, a tail like a dog's, and a hip-wiggling swimming style, according to a new fossil study.
The discovery helps pinpoint the advent of "modern" whale flukes to between 38 and 40 million years ago, scientists say.
Flukes are the two wide, flat triangular lobes on a whale's back end and are made of skin and connective tissue, with bones in the middle.
Scientists have known whales evolved from semiaquatic, four-footed creatures with long, thin tails to today's fully aquatic mammals with fluked tails, no back legs, and flippers instead of front legs.
(Related story: Whales Evolved From Tiny Deerlike Mammals, Study Says [December 19, 2007].)
But it was previously unknown when the tail flukes first arose in the whale family tree.
"What's interesting about this animal is that it had these back legs that it used to push itself through the water," said study author Mark D. Uhen, a paleontologist from the Alabama Museum of Natural History.
"This animal didn't have flukes, but the ones just a little bit younger [geologically] did. So we can really narrow that time frame now."
Uhen's study is detailed in the latest issue of the Journal of Vertebrate Paleontology.
Amateurs found different parts of the newly described fossils over time in Coffeeville Landing, Alabama.
After the various fossil parts were brought to the University of Alabama in 2005, Uhen realized that all the pieces belonged to the same individual of the species Georgiacetus vogtlensis.
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