The fish that walked out of water
The well-preserved remains of creatures with a crocodile-like head and flattened body neatly fill a gap between fish and the first creatures to walk on land.
Previous fossils representing this milestone have essentially been fish with a few land characteristics, or slightly fishy land vertebrates. The newly-found fossils show an animal that sits between the two. Dr. Ted Daeschler, of the Academy of Natural Sciences, in Philadelphia, said: "The find is a dream come true."
The Tiktaalik roseae fossils were found on Ellesmere Island, in Arctic Canada, which was subtropical at the time they were alive.
They provide the missing link between fins and limbs, when animals first walked out of water on to land about 375 million years ago. They have a skull, a neck, ribs and parts of the limbs that are similar to four-legged animals known as tetrapods, as well as fish-like features such as a primitive jaw.
In two articles published in the journal Nature today, Prof Neil Shubin, Dr Daeschler and colleagues describe the fossil that could become an icon of evolution as potent as Archaeopteryx, a transitional fossil between reptiles and birds. "Tiktaalik blurs the boundary between fish and land-living animals, both in terms of its anatomy and its way of life," said Prof Shubin, of the University of Chicago. "This animal is both fish and tetrapod; we jokingly call it a fishapod."
The fossils were recovered from the layered rock of the so-called Fram Formation - deposits of meandering stream systems formed when North America was part of a super-continent that straddled the equator.
They were collected during four summers of exploration in Nunavut Territory, 600 miles from the North Pole.
Members of the team reached the tundra site by a series of aircraft, including a helicopter, and had to endure freezing temperatures and high winds. They carried guns for protection from polar bears.
The skeletal material from several specimens shows that Tiktaalik, ranging from 4ft to 9ft long, had the scales and fins of a fish but the ribs, neck, head and appendage bones like those of a land animal.
Prof Shubin said: "As each piece of Tiktaalik's anatomy was exposed, we began to see how wonderfully intermediate this animal's features were between land and water. "Most of the major joints of the fin are functional in this fish. The shoulder, elbow and even parts of the wrist are already there and working in ways similar to the earliest land-living animals."
The deposits where the fossils were found and the skeletal structure of Tiktaalik suggest that it lived in shallow water and perhaps could survive out of the water for short periods.
Instead of using the traditional Latin or Greek to name the fossil, the scientists asked the Nunavut Inuit people to propose a name. The elders council suggested Tiktaalik (pronounced tic-TAH-lick), meaning a large, shallow water fish.
Dr Richard Lane, of the United States National Science Foundation, said: "Human comprehension of the history of life on Earth is taking a major leap forward. "These exciting discoveries are providing fossil Rosetta Stones for a deeper understanding of this milestone from fish to land-roaming tetrapods." Dr. Marcello Ruta, of the University of Bristol, said: "This amazing discovery has joined many of the dots of a complex picture." (Source: telegraph.co.uk) Epochal fossils found, filling water-to-land evolutionary gap www.chinaview.cn 2006-04-07 09:30:08
BEIJING, April 7 (Xinhuanet) -- Scientists have discovered a group of fossils in the frozen rocks of an island north of the Arctic Circle in Canada, which fills an evolutionary gap between fish and four-legged land animals.
This undated picture shows the preserved remains of a newfound fish fossil with swim fins and a head like a crocodile. (AFP/Nature) The discovery, cited as epochal by other scientists, is detailed in the journal Nature Thursday.
The newfound fossils, including several specimens 4 to 9 feet long, show that the animals bore the scales, gills and fins of fish, but also the ribs, neck 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. "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," one of the discoverers said. "It sort of blurs the distinction between fish and land-living animals."
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.
Scientists have long known that fish evolved into the first creatures on land with four legs and backbones more than 365 million years ago, but they've had precious little fossil evidence to document how it happened. They said the discovery, with its unusually well-preserved and complete skeletons, reveals significant new information about how the water-to-land evolution took place. Enditem