Quirky "fishapod" crawls onto our family tree

U.S. researchers say they have found the missing evolutionary link between fish and land animals: fossils of a strange creature that crawled onto the shore about 375 million years ago.

The fossils, found on Ellesmere Island in Arctic Canada, have the skull, neck, ribs and limb bones of four-legged animals and the primitive jaw, fin and scales of fish, according to a report published today in the journal Nature.

"This really is what our ancestors looked like when they began to leave the water," according to an editorial accompanying the report.

The newly discovered species, 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, one of the co-leaders of the expedition.

"This animal is both fish and tetrapod," Shubin said. "We jokingly call it a fishapod."

The creature lived in shallow waterways, where it hunted for prey with its mammal-like snout and sharp teeth, but it was able to pull itself out of the water for short periods and move around on its limblike fins, the researchers say.

The fossils, ranging in length from 4 to 9 feet, were remarkably well-preserved, allowing the team to examine the joints carefully and to conclude that the shoulder, elbow and wrist joints were sufficiently strong to support the animal'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 paid for the research along with the National Geographic Society and others.

"These exciting discoveries are providing fossil Rosetta stones for a deeper understanding of this evolutionary milestone: fish to land-roving tetrapods," or four-legged creatures, he said.

In the Late Devonian Period 375 to 363 million years ago, the land mass where the fossils were found straddled the Equator and had a climate much like that now in the Amazonian Basin. It was a flat coastal plain with shallow, slow-moving rivers that meandered to the sea.

But as Earth's continental plates shifted, the mass was carried far north, to Canada's Nunavut Territory, more than 600 miles north of the Arctic Circle.

Finding and extracting the fossils presented major challenges, starting with the need to helicopter into the region. Shubin said he and Ted Daeschler, also an expedition co-leader, set out to find transitional animals in the far North because large Devonian deposits are exposed to the weather there without civilization, vegetation or dirt to conceal them: "Up there, it's either rock or ice," he said.

The key breakthrough came on the 2004 expedition, one of five yearly trips, when team members spied the front end of a skull sticking out of a bluff.

The team ultimately found three nearly complete specimens, but they weren't sure of what they had until they returned to the laboratory and started studying the bones.

The creature had a flat skull, with the eyes on top, like a crocodile. But while crocodiles are reptiles, Tiktaalik also had features of a fish.

Moreover, it had a neck, making it the only fish known to have one. "The neck was one of the biggest surprises," said Daeschler, of The Academy of Natural Sciences in Philadelphia. "This freed the skull from the shoulder girdle and gave the animal extra mobility."

Also, at the ends of the powerful fins, the team found wrists and bones similar to fingers. But the fins also contained the thin rods found in fish fins. "Here is a creature with fins that can do push-ups," Shubin said. "This is clearly an animal that is able to support itself on the ground," probably in shallow water and for brief excursions on land. On land, it apparently moved like a seal, he said.

Finally, instead of the tiny rodlike ribs of a fish, Tiktaalik had full-fledged ribs that overlapped one another and could support the body against gravity. It probably had lungs and gills, Shubin said.

Rather than follow the conventional protocol of using Latin for a new species name, the research team asked the Nunavut Council of Elders for suggestions.

It recommended Tiktaalik, which means "a large, shallow-water fish" in the Inuktitut language.

Roseae honors an anonymous donor to the expedition.

Material from The Associated Press and The Washington Post is included in this report.