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April 12, 2006
Fish Out of Water
Scientists have found a fossilized fish that may have been the first critter to crawl out of the water and onto the land. Dubbed Tiktaalik roseae, the species was 4 to 9 feet (1 to 3 meters) long and had the gills and fins of a fish. But its fins included shoulders, elbows, and wrists, like the limbs of land animals. Tiktaalik (say "tic-TAH-lick") also had a crocodile-style skull and the neck and ribs of an early land animal.
Missing link between land and sea?
The scientists say their "fish with elbows" represents a major link in the evolutionary chain leading from ancient fishes to amphibious land animals. According to lead researcher Neil Shubin, "Tiktaalik blurs the boundary between fish and land-living animal both in terms of its anatomy and its way of life." Study co-author Farish Jenkins adds, "This represents a critical early phase in the evolution of all limbed animals, including humans."
Drop and Give Me Twenty, Fish
The researchers found the 375-million-year-old Tiktaalik fossils frozen into stone in Canada, just 600 miles from the North Pole. Yet Tiktaalik made its home in a subtropical swamp, among the shallow streams of an equatorial river delta. But there's really nothing fishy about that. Tiktaalik's bones just drifted with the continent. The land mass that now includes Arctic Canada straddled the equator 375 million years ago.
Tiktaalik was a predator, with sharp teeth and eyes on top of its flat head. The researchers think it crawled over logs, stones, and other obstructions in its swampy home, doing a kind of "primitive pushup," like a seal on ice. Not graceful, perhaps, but you have to crawl before you can walk.
When Fish Ruled the Earth
All of this happened during the Devonian Period, which lasted from around 417 million to around 354 million years ago. That's roughly 140 million years before the first dinosaurs. Paleontologists sometimes call the Devonian the "Age of Fishes." The first jawed fishes and the first sharks date from the period. So do the first "lobe-finned" fishes--the type scientists say gave rise to us groundpounders.
The most famous lobe-finned fish is the coelacanth, a.k.a. the "living fossil" fish. Scientists used to think coelacanths were extinct. But coelacanths thought otherwise. In 1938, a museum curator in South Africa found a live specimen in a local fisherman's catch.
Posted by sue at April 12, 2006 11:49 AM