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There Was a Dangerous Purpose Behind T. Rex’s Tiny Arms

The dinosaur's puny arms were nothing to laugh at.

The Tyrannosaurus rex is revered as one of the most fearsome creatures to inhabit the earth, with an average weight of six tons and the power to tear off 500 pounds using its massive jaw. But one researcher believes the dinosaur’s most ridiculed body part may have been just as vicious: the T. rex’s puny, undersized arms.

According to Steven Stanley, a paleontologist at the University of Hawaii at Manoa, T. rex arms were used to slash prey in close proximity to the dinosaur. The arms, which were approximately three feet long, featured crescent-shaped talons that could be used to inflict mortal wounds to prey. And the short arm length was actually more beneficial for slashing, considering the size of T. rex’s head.

“Its short, strong forelimbs and large claws would have permitted T. rex, whether mounted on a victim’s back or grasping it with its jaws, to inflict four gashes a meter or more long and several centimeters deep within a few seconds,” Stanley reported at a Geological Society of America meeting in October 2017. “And it could have repeated this multiple times in rapid succession.”

In the past, T. rex arms had been believed to be nothing more than holdovers after years of the predator’s evolution, like wisdom teeth for humans or wings for flightless birds. But several factors led Stanley to conclude that the arms of the premier predator of the prehistoric era may have potentially been useful.

t rex

A new discovery shows that the arms of a T. rex may have been more useful than previously suspected. (Credit: Getty Images/Science Photo Library RF)

In addition to the practicality of the T. rex’s arm length, Stanley explained that the dinosaurs head was part of an “unusual quasi-ball-and-socket joint” that let the arms have plenty of mobility. He also argued that the relatively tiny limbs packed a punch, comparing them to the legs of a six-foot man in terms of length and width.

Even with new light shed on the formidability of the T. rex’s arms, there are still skeptics that oppose Stanley’s conclusions. Dr. Jakob Vinther, a paleobiologist at the University of Bristol, told National Geographic the arms were more likely used for mating than attacking prey.

“It seems illogical to me to use such small arms to slash with,” Vinther said.

Thomas Holtz, a tyrannosaur expert at the University of Maryland, College Park, agreed that the arms could be a dangerous tool, but said the length and position of the limbs would require the T. rex to “basically have to push its chest up against the side of the victim,” he told National Geographic. It’s more likely that the T. rex would’ve used its strongest asset, its jaws, as opposed to its arms for attacking, says Holtz.

Either way, the revelation that the T. rex had another potential weapon at its disposal is one in a string of recent discoveries about the beast, giving reason to believe there’s still more to uncover about one of history’s greatest predators.

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