U.S. researchers have found fossils of what they say is a missing evolutionary link between fish and land animals -- a strange creature that first crawled onto the shore about 375 million years ago.
The fossils, found on Ellesmere Island in Arctic Canada, suggest the limbs, skull, neck and ribs of four-limbed animals, but also the primitive jaw, fin and scales of fish, scientists reported today in the journal Nature.
"This really is what our ancestors looked like when they began to leave the water," said an accompanying editorial by zoologist Jennifer A. Clack of the University of Cambridge and biologist Per Erik Ahlberg of Uppsala University in Sweden.
The newly discovered species, called Tiktaalik roseae, "blurs the boundary between fish and land-living animal both in terms of its anatomy and its way of life," said biologist Neil Shubin of the University of Chicago, a co-leader of the expedition.
The creature lived in shallow waterways, where it hunted for prey with its crocodile-like snout and sharp teeth, but was able to pull itself out of the water for short periods of time and move around on its limb-like fins, scientists said.
The specimens, ranging from 4 to 9 feet long, were remarkably well-preserved. The scientists were able to examine the joints and to conclude that the shoulder, elbow and wrist joints were strong enough to support the creature's body on land.
"Human comprehension of the history of life on Earth is taking a major leap forward," said H. Richard Lane of the National Science Foundation, which funded the research along with the National Geographic Society and other groups.
"These exciting discoveries are providing fossil Rosetta Stones for a deeper understanding of this evolutionary milestone -- fish to land-roving tetrapods," he said.
In the late Devonian period, nearly 400 million years ago, the landmass where the fossils were found straddled the equator and had a climate much like that now found in the Amazonian basin. It was a flat coastal plain with shallow, slow-moving rivers that meandered to the sea.
"This kind of shallow stream system seems to be the place where many features of land-living animals first arose," said expedition co-leader Ted Daeschler of the Academy of Natural Sciences in Philadelphia.
But as Earth's continental plates shifted, the mass was carried north to Canada's Nunavut territory in the Arctic Ocean.
