The T.rex was one of the most fearsome predators ever to walk the earth, with massive jaws and powerful legs. But those famously stubby little arms? Scientists have finally come up with a solid explanation.
A team of researchers from University College London and Cambridge University looked at 82 species of theropods, the group of two-legged, mostly meat-eating dinosaurs that includes the T.rex. They found that shorter arms appeared in five different dinosaur groups, and in each case, the shrinking arms seemed to go hand in hand with bigger, more powerful heads and jaws.
The T.rex wasn’t alone either. The Carnotaurus, another large predator, had arms even tinier than the T.rex, which is pretty remarkable when you think about it.
So what caused this? The researchers think it comes down to diet and hunting. Around the same time these dinosaurs were evolving, their main prey, the giant plant-eating sauropods, were getting bigger and bigger. To take down such enormous animals, predators needed a more effective weapon than their arms. Their jaws became the main tool for attacking and holding onto prey.
As the jaws got more powerful, the arms became less and less useful. Over millions of years, they simply shrank.
“The head took over from the arms as the method of attack,” said lead researcher Charlie Roger Scherer, a PhD student at UCL. “It’s a case of ‘use it or lose it’.”
He also pointed out that trying to grab a 30-metre-long sauropod with small claws was never going to be that effective anyway. Enormous snapping jaws, on the other hand, were a very different story.
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