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Odd reptile with freaky arms that lived 212 million years ago ‘stretches the bounds’ of evolution

An artist’s rendition of Drepanosaurus. (Victor Leshyk/Yale Office of Public Affairs & Communications)

The giant anteater is a peculiar excavator. Unlike most mammals that use their hands to dig, by scratching or jostling their way through dirt, anteaters use a two-part motion biologists call a ‘‘hook-and-pull.” First, the anteater wedges its fat front claws into a crack in a termite mound or decomposing log. It then flexes and retracts its arm, like a shaggy backhoe, to tear a hole wide enough to slurp up insects with its 2-foot tongue.

Among living mammals, only anteaters and pangolins are thought to use the hook-and-pull technique. But a reptile named Drepanosaurus may have used a similar digging method 212 million years ago. And as strange as the giant anteater is — it can flex its tongue 160 times a minute, and instead of producing its own stomach acid the anteater digests with the formic acid from consumed ants — Drepanosaurus was weirder.

The creature was neither dinosaur nor mammal, but a small, insect-munching reptile. It had a claw-like structure on the end of its tail. And its very anatomy, specifically the structure of its forearms, broke a long-standing rule of reptile, bird and mammal bones.

“Ecologically, Drepanosaurus seems to be a sort of chameleon-anteater hybrid, which is really bizarre for the time,” said Yale University researcher Adam Pritchard in a statement. Pritchard and his colleagues at Stony Brook University, and various other American universities recently published a study in the journal Current Biology.

You, like all other four-limbed animals, as diverse as frogs and Tyrannosaurus rex and elephants, have two bones in your forearm: the radius and ulna. In most animals, including humans and T. rexes, the pair of bones run parallel to each other and are of approximately equal size.

Not so for Drepanosaurus, the scientists pointed out in their new paper.

The study described Drepanosaurus fossils found in New Mexico’s Hayden Quarry(The only other known Drepanosaurus fossils, discovered in Italy three decades ago, were badly mangled.) What struck the paleontologists was not only the large, hooked claw the reptile sported or its strange tail  in addition, the proportions of the animal’s forelimbs seemed to be off.

As the scientists put it in their paper, the distorted, asymmetric bones showed a “construction utterly unlike the standard tetrapod condition.” That is, where it should run parallel, the ulna swerved far away from the radius. That bone was much larger than its usual partner, too.

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“This animal stretches the bounds of what we think can evolve in the limbs of four-footed animals,” Pritchard said. “It possesses a totally unique forelimb.”

By today’s standards, Drepanosaurus is odd. But as a creature of its time — the Triassic — it was mostly normal. In the millions of years that followed a massive extinction event, the Great Dying, unconvention ruled and lizard-pigs thrived.

Nicholas Fraser, a vertebrate paleontologist at the National Museums Scotland who was not involved with the research, described the Triassic period as a “melting pot of experimentation” to the BBC.

Though the anatomical tweak might seem insignificant, four-legged creatures have existed for some 375 million years. And the first animal to diverge so far from the forearm blueprint was Drepanosaurus. “Here is another animal which is completely unconventional in the way it has got this system of bones in the limb to help it dig,” Fraser said.

Pritchard and his team said they will continue to excavate the New Mexican fossil quarry, remaining on the hunt for other strange Triassic reptiles.

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