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Science & Crypto : Oldest evidence yet of fish moving to land
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 Message 1 of 3 in Discussion 
From: MSN Nicknamebreeze_tioga  (Original Message)Sent: 4/7/2006 1:54 PM

In the frozen rocks of an island 800 miles from the North Pole, scientists have discovered a group of fossils that clearly mark one of the most crucial events in human evolution: a moment in time some 375 million years ago when primitive fish first began moving from the world's oceans to the land.

The fossils show that the animals bore the scales, gills and fins of fish, but also the ribs, neck, rudimentary ear bones and primitive limbs of what ultimately would become the arms and legs of the first land animals -- the ancestors of all reptiles, dinosaurs, birds and mammals, including humans, the scientists say.

The primitive fish are the most important evidence yet discovered for a transitional life form that developed along the path of evolution by adapting in the water to the new land environment they encountered, other experts say.

Three paleontologists -- Neil Shubin of the University of Chicago, Edward Daeschler of Philadelphia's Academy of Natural Sciences and Farish Jenkins Jr. of Harvard -- chipped the fossils from the rocks near the ice-bound shores of Ellesmere Island in the Canadian territory of Nunavut in 2004, two years after first uncovering traces of them during an expedition to the Arctic. The fossils ranged in size from 4 to 9 feet.

"What we found in the rock was clearly a fish, but it had a long flat head with its eyes on top like a crocodile, a beautiful shoulder, a beautiful elbow and a beautiful wrist," Shubin said in an interview.

At the ends of the fins were bones suggestive of developing fingers, and at the base of the fossils' heads were bones that appeared to be the forerunners of a flexible neck. Their broad, robust ribs showed how well their bodies could handle life on land. The scientists also noted that the fishes' gills were modified to rely less on oxygen exchange in the water and showed indirect evidence for the appearance of lungs with the ability to breathe air on land.

The evolved body allowed the fish to climb out of the shallow waters that lapped at tidal flats, estuaries and mud banks and spend time hunting for prey on land, Shubin said. "In the water it had no need to counteract gravity, but in the mud flats its bony fins -- like primitive legs -- could push it along after invertebrate prey, doing a kind of primitive pushup much like a seal on ice."

The scientists named their fish species Tiktaalik roseae after the Inuit word for "large freshwater fish" and the name of an anonymous donor who helped finance the research. The species lived during the late Devonian period when the northern land masses, including what became Ellesmere Island, were located near the equator.

Their report, cited as epochal by other scientists, is appearing today in the journal Nature.

"Shubin and his colleagues have found a transition that is one of the most important evolutionary events in the history of vertebrate animals that made it onto the land -- perhaps in the history of life itself," said Charles Carroll, a noted paleontologist at Canada's McGill University, in an interview.

Another paleontologist who specializes in fish evolution, Jenny Clack of Cambridge University in England, said in a commentary also published today in Nature that Tiktaalik marks "a link between fishes and land vertebrates that might in time become as much of an evolutionary icon as the proto-bird Archaeopteryx."

"This is another gap closed that a deity no longer needs to fill," Clack said in an e-mail discussion on evolution with The Chronicle. "The fossil combines features of fish and tetrapods such that it fits perfectly between the two."

Nearly 20 years ago, Clack and Michael Coates of the University of Chicago found fossils of a fish named Acanthostega that lived in Greenland some 15 million years after Tiktaalik and was also hailed as transitional when it was described. But, unlike Tiktaalik, its fins were only for swimming, its bones could not support weight on land and the creature had no wrists or ankles.

The Shubin team's discovery, Coates said in an interview, "really fills a significant gap in the evolution of tetrapods because its bony fins clearly show us a pre-pattern for their transformation to limbs while it was still living largely in the water."

The end of the Devonian period, he said, "was a time when Planet Earth was undergoing major changes, along with changes in the atmosphere while complex ecosystems were emerging on the land and life in the swampy waters was preparing to exploit the new nutrients."

Tiktaalik's body was apparently well-adapted to life in that environment, chasing prey in the water as it swam, Coates said, but finding new prey among the invertebrate organisms that inhabited the sea's muddy margins as it humped itself onto the new land.

John McCosker, chairman of aquatic biology at the California Academy of Sciences in San Francisco, is no paleontologist, but he has studied fish evolution, and after reading the Nature papers he commented:

"These fish help to fill in the gaps in the fossil record that marks the transition of life from water to land, and the discoveries provide additional evidence that disputes the oft-heard and unfounded criticism made by some creationists that adequate evidence doesn't exist to support these proposed ancestries.

"The only thing better than this would be to catch a live one."

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 Message 2 of 3 in Discussion 
From: MSN NicknameSmigChickSent: 4/10/2006 7:29 PM

 Message 3 of 3 in Discussion 
From: JagSent: 7/19/2006 12:40 PM
Interesting...  Made me think of a lungfish, but they don't have the neck and wrists and such...  hmmmmmm