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Fossil fills gap in move from sea to land

New findings in Canada, coming out Thursday, show an ancient fish that could lift itself up.

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Paleontologists have discovered the fossil remains of a 375-million-year-old fish that fills a crucial gap in the evolutionary history of Earth's four-limbed creatures.

Among the fish's most distinguishing features: the skeletal beginnings of shoulders, wrists, and legs that signal a future move to land.

Gently scratched from soil layers on desolate Ellesmere Island in Canada's Nunavut Territory, the new fossils could join the ancient bird archaeopteryx as an icon for evolution in action, some researchers say.

"It's really an amazing find," says Hans-Dieter Sues, associate director of science at the Smithsonian Institution's National Museum of Natural History in Washington.

Scientists have long surmised that four-limbed land animals evolved from early fish. In recent years, they have been slowly closing the fossil gap between these fish and the first land vertebrates. But existing fossils have failed to fill an important, 10-million-year hole in the record, when the fish were undergoing significant physical changes.

Thus, the appearance of the new species is likely to become "a textbook example of the transition" from fish to four-limbers, known as tetrapods, says Edward Daeschler, a paleontologist with the Academy of Natural Sciences in Philadelphia. He and Neil Shubin, of the University of Chicago, led the team that made the discovery, which will publish its findings Thursday in the journal Nature.

Scientists can look at fossils on either side of the gap, then sit back "and philosophize on what intermediate forms should look like," Dr. Sues says. This single find, he continues, clears much of the fog from that view.

The team named the species Tiktaalik roseae, using an Inuit word for large, shallow-water fish. During its heyday, it lived in freshwater streams and ponds under conditions far warmer and more lush than today - at the time, what is now Ellesmere Island was part of the continent Laurentia, which straddled the equator.

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