Photo: About 200 million years ago in what is today New Mexico, a Drepanosaurus used its massive claw and powerful arm to rip away tree bark and expose the insects within. Credit: Painting by Victor Leshyk About 200 million years ago, a reptile resembling a chameleon wielded a digit on each of its front legs with a massive claw, and used that claw as a digging tool in a manner similar to that of modern anteaters.
However, the oversize claws weren't even the weirdest part of this animal's forelimbs, according to a new study describing fossils of the unusual appendages.
The front limbs of most tetrapods -- four-limbed animals with backbones -- share certain similarities in bone arrangement and shape. But this unusual reptile's forelimb structure diverged dramatically, suggesting that early tetrapod limbs may have been more diverse than previously suspected. [Image Gallery: 25 Amazing Ancient Beasts]
The first fossil of this ancient, chameleon-like reptile -- known as Drepanosaurus and measuring about 1.6 feet (0.5 meters) in length -- was found in Italy in the 1970s and was described in 1980, according to study author Adam Pritchard, a postdoctoral fellow with the Department of Geology at Yale University.
But the fossil, though mostly preserved, was badly crushed, Pritchard told Live Science.
Scientists managed to isolate individual bones just enough to suggest the creature had odd front limbs. But to reconstruct the limbs to see what they actually looked like would take more, uncrushed, fossil material.
That material didn't emerge until decades later.
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In 2010, Pritchard began investigating fossils excavated by the study's other co-authors, in Ghost Ranch, New Mexico. He and his colleagues identified three Drepanosaurus specimens that were preserved in 3D, providing a first glimpse of the forelimbs that had intrigued scientists 30 years earlier.
Pritchard explained that tetrapod forelimbs follow a basic plan: a single bone, the humerus, attaches to the shoulder. Attached to the humerus are two elongated parallel bones, the radius and ulna, which meet a series of shorter wrist bones at the base of the hand.
Drepanosaurus, however, had two differently shaped bones extending from the humerus that were not parallel. One was shaped like a crescent moon, Pritchard said. Attached to this crescent-moon bone were two long and slender wrist bones that were much longer than the other wrist bones.
"The idea we confirmed with the new fossils was that the crescent moon bone was, in fact, the ulna," Pritchard said. "Drepanosaurus maintains the traditional bones that make up the forelimb, but they're radically altered."
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