Persons explains that it was perfectly possible Osborn could have been right. If male T. rexes – which are notoriously difficult to identify – had turned out to have arms that looked different to female ones, it would make sense that they were using them for sex. “Now, that’s not the way things have gone down,” he says. Instead, as more and more individuals have been uncovered – there are now at least 40 – scientists have confirmed that they all have the characteristically small arms and they always look pretty much the same.
Another, potentially comical, possibility is that T. rexes may have used their little arms to get up off the ground. With up to 15,500lb (7,031kg) bodies – equivalent to the weight of a large African elephant – they may not have found it easy to manoeuvre out of a resting position, or get back on their feet in the event that they fell over. (Many living animals struggle with this to this day, such as tortoises, which often rock themselves upright when they end up on their backs.)
“So when they were rising from a crouched position, they could use the arms to do a tiny tyrannosaur push-up,” says Persons. However, there is a small flaw with this theory – the carnivore’s arms wouldn’t actually have helped that much. “You’ve got to understand that that really only helps the tyrannosaur with the first two feet. And then it’s got like another 15 feet to go off the ground,” he says.
Another controversial idea, put forward by a single scientist in 2017, is that adults like the Wankel Rex may have used their stubby arms as weapons – perhaps holding their victim in their jaws or pinning it down with their bodyweight, before ripping and slashing at it. Underpinning the idea is that though they’re tiny, T. rex‘s arms are surprisingly muscular. He calculated that even with its 3ft (0.9m) limbs, these eviscerating actions could have done some serious damage, creating gashes several centimetres deep and at least a metre long in a matter of mere seconds.
“Now I personally think the arms are just too ridiculously short for that to make sense,” says Persons.
However, there is also the possibility that they had no function whatsoever – T. rex’s tiny arms were the last vestiges of once-useful appendages that had long ceased to be necessary. If they were simply hangovers from another time, like the human tailbone, the world’s most terrifying predator may have had an ever more bone-chilling future: eventually evolving to lose its arms altogether, to resemble a kind of horrifying land-shark.