T rex may have used its small arms for “vicious slashing”

As towering as it would have been, the threat of a Tyrannosaurus Rex has long been undermined by the thought of its small, ineffectual, strange-looking arms.

But new research suggests that these disproportionate ­– often mocked – limbs were more useful for killing that a first glance would suggest. According to a paper presented at the annual conference of the Geological Society of America, the T rex’s metre-long arms could have been used for “vicious slashing” of cornered prey.

Paleontologist Steven Stanley from the University of Hawaii at Manoa argues that the limbs – generally seen as a vestigial hangover from a larger-armed forebear – could have actually been an adapted asset for close-quarters killing.

Stanley points to the dinosaur’s large coracoid, part of the shoulder bone that stabilises arm movement, as evidence that the T rex’s arms were much stronger than many believe. He goes on to claim that the creature’s humeral head, around the shoulder socket, were “part of an unusual quasi-ball-and-socket joint that would have provided considerable mobility for slashing”.

The limbs would apparently have been slightly longer than the leg of a six-foot man, with a similar girth, and robust enough to sustain the impact of slashing. Stanley also argues that the unusual number of digits on each arm – just two, instead of three – would have helped the dinosaur to exert 50% more pressure from each 10cm, sickle-shaped claw.

“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 metre or more long and several centimetres deep within a few seconds,” Stanley writes, “and it could have repeated this multiple times in rapid succession.”

Other scientists are less sure about the practicalities of using these limbs for attacking: “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,” palaeontologist Thomas Holtz from the University of Maryland told National Geographic.

While it may have been difficult for an adult T rex to get in a position where it could inflict some “vicious slashing”, Holtz does acknowledge that younger specimens could have made use of the maneuver: “The strike zone would be proportionately larger in a young T rex – and going after smaller prey would mean the force required to kill the victim would be less.”

Does the thought of a T rex flailing at cornered prey with small arms do anything to make those disproportionately limbs any less comedic? No. No it does not.