T. Rex Used Its Tiny Arms to 'Viciously Slash' Prey With Huge, Deadly Gashes

Yes, the teeth are terrifying, but you're not taking the arms seriously enough. Oli Scarff/Getty Images

Sure, it's fun to mock the short, stubby arms of the otherwise fearsome Tyrannosaurus rex, but new research suggests maybe you don't want to do so anywhere near those short, stubby arms—which could have inflicted giant gashes, three feet long and a couple inches deep, on the dinosaur's prey.

Paleontologist Steven Stanley, a scientist at the University of Hawaii, recently made the case that the T. rex may have gotten violent with its arms. In a presentation at the Geological Society of America's annual conference in late October, he said the famous dinosaur's arms weren't quite as puny as we imagine them to be—and that in fact they possessed several characteristics that would have made them exceptionally unpleasant to encounter.

Stanley was arguing against a trend in recent science that has been playing down the importance of the tiny arms, which are often referred to as "vestigial," evolutionary leftovers that are no longer used but haven't entirely disappeared, like the stub of our tailbone.

Stanley countered that first of all, the arms weren't nearly as tiny as we tend to consider them—each would have been longer than three feet—and that other characteristics made them much more powerful than we've given them credit for.

There were very strong bones inside those arms, which would have stood up well to vigorous activity. Stanley also believes that in close encounters with prey where the T. rex wouldn't have had much room to maneuver, its shorter arms would have been more effective to wield.

And given what's on each end of those tiny arms, Stanley said their forte would have been slashing. That's in part because the T. rex's shoulder joint, unusual for dinosaurs of its type, was almost a ball-and-socket joint like those in our own shoulders that let us swing an arm with enough mobility to trace out more than a half-sphere.

At the other end, Stanley saw vicious knives that would have turned the maneuverability and force of those tiny arms into weapons capable of delivering huge gashes. Each claw was about 3 inches long and shaped like a talon to inflict the most damage. Moreover, unlike its near relatives, the T. rex had only two claws on each hand rather than three. That sounds like a shortcoming, but it wasn't—each of its two claws struck with half again as much force because the blow was spread over two weapons.

Still, Stanley has not convinced all the tiny-arm jokers. "I would expect it could cause some decent damage if it struck, but in order to deploy [the arm], tyrannosaurus would basically have to push its chest up against the side of the victim," paleontologist Thomas Holtz of the University of Maryland told National Geographic. "In such a position the tyrannosaur wouldn't be able to use its far more powerful armament: its massively powerful jaws."

Maybe stay out of reach of both arms and the jaws of a T. rex, just to be on the safe side.