Bizarre prehistoric reptile with giant claw

Armbones of Drepanosaurus are unique among terrestrial vertebrates

This is how Drepanosaurus could have looked about 200 million years ago. Conspicuous are his claw-reinforced front-lines. © Cell Press
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Unique Anatomy: A reptile living 200 million years ago turns out to be very unusual thanks to new fossil recordings. Because the tree-living Drepanosaurus had shovel-like broadened forearm bones with gigantic claws on the fingers. This anatomy is unique among the terrestrial vertebrates - helping the reptile gain access to insect nests and other prey in the wood, researchers report in the journal Current Biology.

In their approximately 375 million years long history, the terrestrial animals have already produced several bizarre variants. They include a "Speedy Gonzales" dinosaur with Sprinter anatomy and grailbars, lizard-eating giant frogs, and a dinosaur composed like set pieces from other animals.

Contradiction to the anatomical rule

The forelegs proved to be particularly versatile and versatile: they were converted into wings, grab arms, grave organs or swim fins, depending on how they lived. Despite all the variation, however, one thing was always the same in the blueprint: The forearm bones Elle and Spokes were always parallel to each other and met in the wrist on a series of short, knobbly carpal bones.

However, the Drepanosaurus unguicaudatus, which lived about 200 million years ago, did not follow this rule, as fossils discovered in New Mexico first prove. This tree-dwelling, about 50-centimeter-long reptile resembled a large chameleon with a slender neck and a strong long tail.

Bucket arm with giant claw

Most unusual, however, were the forelegs of this prehistoric reptile: the ulna was widened like a shovel and curved to support powerful muscles. In the almost immovable elbow, this bone stood almost perpendicular to the smaller, thinner spoke. How to compensate for the wrist bones of the reptile were greatly extended. display

The forearm bones of the Drepanosaurus are unique among the tetrapods in two ways: the ulna and radius are not parallel and the carpal bones are extremely elongated. Adam Pritchard et al. / Current Biology

"Thereby, Drepanosaurus contradicts two rules that used to apply to the tetrapod limbs, " says first author Adam Pritchard of Stony Brook University in New York. This anatomy of the arms is unique among the terrestrial vertebrates.

Hooked up and torn up

More about the purpose of this bizarre arm form betray the big claws of the reptile, which are crowned by an almost huge hook-like bent claw on the second finger. Taken together, these features suggest that Drepanosaurus had tremendous power in its forelegs and, thanks to its claws, was able to tear apart even hard materials.

The prehistoric reptile is similar to today's anteaters: "The anteaters use a special grave technique, in which the animals hook their enlarged claws in a substrate and then the entire arm kr Withdraw, "explains Pritchard. Similarly, the tree-dwelling drepanosaurus might have torn up bark and wood crevices with its claws and forelegs to access insects and other prey.

The exciting thing about it: The Drepanosaurus is the only known terrestrial vertebrate animal that possesses such anatomy and technology before the evolution of the first grave animals in the palaeogene. There is a gap of 150 million years between the prehistoric reptile and the development of the first antbreeds. "This confirms the great importance of the Triassic as the time in which not only many tribal lineages have their origin, but in the many ecologic niches emerged, " emphasize Pritchard and his colleagues. (Current Biology, 2016; doi: 10.1016 / j.cub.2016.07.084)

(Cell Press, 30.09.2016 - NPO)