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Forgotten fossils reveal leggy legacy.

Paleontologists normally discover fossil treasures while chipping at rock, but some of their best finds pop up during searches through old museum drawers. After sifting through the collections of several British museums, one researcher has identified the remains of the earliest footed animal, documenting a critical step in the evolutionary journey our ancestors tooks as they left the oceans for the land.

All of the rediscovered bones originally came from a Scottish site dating back to the Frasnian stage of the late Devonian period, about 370 million years ago. In the past, scientists who examined some of these specimens had identified them as fish remains. But in the Nov. 28 NATURE, per E. Ahlberg of the University of Oxford says the bones have characteristics linked to the tetrapods, or four-footed animals. Scientists believe tetrapods evolved from fish with lobed finds and were the first vertebrates to crawl onto land.

Ahlberg describes one of the fossil bones as a tibia (leg bone) that "represents the earliest known terapod-type hindlimb." This find pushes back the origin of tetrapods by about 10 million years.

Ahlberg has also identified a humerus and jaw fragments from etrapods or their close relatives.

Scientists cannot tell whether all of the bones came from the same type of animal, but if one creature did wear these different parts, it might have looked like a cross between a fish and a tetrapod, says paleontologist Jennifer A. Clark, who studies early tetrapod evolution at the University of Cambridge in England. While the tibia clearly belongs to a leg, the humerus preserves some fish-like characteristics and may have formed part of a fin, suggesting this animal had feet in back and fins in front. In her studies of the next-oldest tetrapod, an animal from Greenland, Clack has found a similar mosaic of fish and tetrapod traits.

"What seems to be happening is that the boundary between fish and tetrapods is becoming rather blurred," she told SCIENCE NEWS.

Because they display a mixture of characteristics, the Greenland and Scottish finds support the idea that the tetrapods' fishy forebears developed legs for some purpose other than walking on land. Clack says legged fish may have used discrete, toe-like digits to grasp vegetation while waiting to ambush their prey. That hypothesis challenges the standard theory that legs evolved from fins when fish began dragging themselves between pools of water separated by dry land.
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Title Annotation:remains of footed animals
Author:Monastersky, Richard
Publication:Science News
Date:Nov 30, 1991
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