Did “Raptor” Killing Claws Evolve For Climbing?

In one of the early scenes of Jurassic Park, the fictional paleontologist Alan Grant terrorizes a child visiting his dig site with a Deinonychus claw. If the dinosaurs were still alive they would have used the enlarged claw on their second toes to rip open the boy and eat his guts, Grant says, a fate Grant himself almost meets when he encounters the cloned predators later in the film. But did Deinonychus and its relatives like Velociraptor really use their claws to tear open their prey?

As part of the U.K. documentary miniseries The Truth About Killer Dinosaurs, a team of paleontologists created a reconstruction of a Velociraptor leg. When they tested it to see if the dinosaur's claw could have been used to disembowel prey, they found something they did not expect. The huge foot claw of the "raptor" dinosaurs was not very good for slashing. Instead, it seemed to be better adapted as a grappling device, like a hook that could be used to hold onto or pin down prey. The claw may have even had a "locking" mechanism that would have kept the claw latched into the victims of Velociraptor, thus allowing the predator to dispatch its prey with its hands or jaws.

Some of those same researchers have now followed up with a new study published in a special all-dinosaur edition of the Anatomical Record, this time looking at a hand claw from Velociraptor. What they discovered was that the hand claw of the predatory dinosaur was also well-adapted to anchoring into surfaces. It was even strong enough to have held the dinosaur up if it attempted to climb a tree. Velociraptor lived in an arid landscape and so it probably did not actually engage in this behavior, but it is something Hollywood directors might want to take into account when they start filming Jurassic Park IV.

There is still much more work to do (the scientists have yet to test their hypotheses with other dinosaurs related to Velociraptor or even model how the entire hand might have worked while latching onto prey or a surface), but the studies have important implications for the evolution of birds. Velociraptor and Deinonychus are among the dinosaurs most closely related to birds, and they evolved from much smaller ancestors. It may be that the "killer claws" of these dinosaurs allowed the early, small members of this group to climb trees. Once up in the canopy, some of these dinosaurs, like the ancestors of Microraptor, might have evolved the ability to fly. The fact that such claws also allowed these dinosaurs to better hold onto and anchor themselves into prey was just a matter of putting a pre-existing trait to a new use and may have led to the evolution of the larger predatory forms like Utahraptor.

Birds did not directly evolve from Velociraptor, Deinonychus, or Microraptor, but the way these dinosaurs used their claws might provide a crucial clue to how their close avian relatives evolved. Paleontologists have debated for years whether birds evolved flight from the "trees down" or the "ground up," and these new studies throw some tentative support to the "trees down" camp. Hopefully further studies will soon be undertaken to flesh out this hypothesis.

Riley Black | | READ MORE

Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American.