An expert paleontologist has claimed that the stubby arms of the Tyrannosaurus rex were actually vicious weapons.
Last year it was found that a separate species of dinosaur, the Gualicho shinyae, evolved the same puzzlingly small arms independently of the T-rex – suggesting the tiny limbs were not vestigial and stepping up efforts to deduce their purpose.
A paper by Dr Steven M Stanley, from the University of Hawaii, now suggests that T-rex’s seemingly comical arms were “not functionless but adapted for vicious slashing”.
Stanley, who presented his findings at a meeting of the Geological Society of America in Seattle, said the evidence suggests the arms were very strong. Meanwhile, at a length only slightly longer than the leg of a 6ft man, they would have been ideal for close-quarter slashing – with huge damage caused by 10cm, sickle-shaped claws.
“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 centimetres deep within a few seconds,” wrote Stanley. “And it could have repeated this multiple times in rapid succession.”
Stanley explains that Tyrannosaur ancestors used their longer limbs for grasping, but a T-rex’s jaws replaced this function.
“No longer being selected for, the arms were selected against: the expansion of the head deprived them of nutrition in a zero-sum game,” said Stanley. “Then, as the arms approached their final size, natural selection kicked in opportunistically and put them to good use for slashing at close quarters.”
Other experts at Stanley’s presentation are unconvinced however, with Jakob Vinther, from the University of Bristol, who attended, saying it was “illogical” to him.
He suggested the arms might have a more minor purpose, perhaps to hold on to a mate during sex – a claim Stanley indicated would be too dangerous given the claws’ sharpness.
It’s a debate that will rage on.