Prehistoric fish used fins to crawl out of sea

New find is called missing link to later land animals

April 06, 2006|By DENNIS O'BRIEN | DENNIS O'BRIEN,SUN REPORTER

Researchers have unearthed fossils of a fish with limb-like fins in the Canadian Arctic -- a crucial missing link that might help determine how ancient sea animals evolved and made the transition to living and walking on land.

Named Tiktaalik roseae, the creature had the skull, neck and ribs of the earliest land-based animals with limbs, but the fins and scales of a fish.

It also had sharp teeth, a head like a crocodile and limbs that gave it the ability to crawl over logs and other obstructions in its swampy world. So, scientists believe it could have been the first creature to crawl on land.

"Every limbed animal on Earth goes back to this, including us," said Ted Daeschler, a vertebrate paleontologist at the Academy of Natural Sciences in Philadelphia and a co-leader of the expedition that made the discovery.

The animals were 4 to 9 feet long and lived 375 million years ago, when the land mass where they were found was near the equator. That made it a subtropical swamp much like the Mississippi Delta -- a flat plain with rivers that flowed to the sea, Daeschler said.

The researchers found fossils of the three skulls, as well as jawbones and limb-like pectoral fins of several other specimens in some frozen, sedimentary rocks after a five-year search of the Arctic for fossils of ancient fish. In all, they found the remains of 10 creatures.

The team, hampered repeatedly over the years by bad weather, uncovered the fossils in 2004, on its fourth trip to the region. They were in a valley on Ellesmere Island, more than 600 miles north of the Arctic Circle.

"Remote is the best way to describe the area. There was nothing anywhere near it," Daeschler said.

He said the team knew that it had found a good spot when a member spotted a few small fossils near what was once a riverbed. "We had our eye on this area for quite some time," he said.

The creature is a key link in the transition from aquatic to land-based creatures -- a process that took about 30 million years, Daeschler said.

The 10 specimens the researchers discovered were probably freshwater fish that died together when flooding washed mud and sediment into the area, destroying their habitat, Daeschler said.

The creatures could use their powerful pectoral fins to raise themselves and plod along on land, he said.

"This is still a fish, but it's illustrating features we attribute to limbed animals," he said. "There's nothing alive today that's really like it at all."

The fossils were found in the Nunavut Territory, and the researchers settled on the name Taktaalik because it means "large, shallow-water fish" in the Nunavut language. The name roseae is derived from an anonymous donor who helped fund the expedition. Additional funds were provided by the National Science Foundation and National Geographic.

The findings were published yesterday in the journal Nature. Co-authors included researchers from Harvard University and the University of Chicago.

Experts who study ancient fish say the discovery sheds light on the key evolutionary step from sea to land.

"They're pretty weird things, let's face it," said John Maisey, a fish and fossil expert at the American Museum of Natural History who was not involved in the discovery but reviewed the report. "These kinds of discoveries are pretty rare, and this is a big one."

The finding represents something entirely new in the study of ancient fish -- a creature equipped with a joint-like pectoral fin that gave it an ability to lift itself. "What we've got is a fish with elbows, if you like," Maisey said.

He added that he was amazed by the near-original composition of several skulls. "The beauty of it is, they're so complete. You can study the anatomy of so much of this beast," he said.

The presence of both fins and primitive limbs shows that the creature wasn't a particularly good swimmer or very agile on land, Maisey said. But its ability to traverse both gave it an advantage, enabling it to make brief forays to escape predators in the water.

"It wasn't so much a case of conquering the land as escaping from the water," he said.

The prehistoric seas were particularly dangerous places for smaller fish. Predators included sharks and Rhizodonts, a fish up to 20 feet long, he said.

"There was a lot they would have had to get away from."

dennis.obrien@baltsun.com

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