The tiny arms of Tyrannosaurus rex have supplied cartoonists and comedians with endless gags since its discovery, but the giant dinosaur may have had the last laugh.
A new study suggests meat-eating dinosaurs such as T-Rex evolved such small appendages because their terrifyingly huge heads meant they no longer needed powerful claws to rip into prey.
Experts at University College London (UCL) and the University of Cambridge studied data from 82 species and found smaller arms were closely linked to the development of large, powerful skulls and jaws.
The researchers believe that the evolution of gigantic sauropods, such as Alamosaurus, and other large herbivores, may have resulted in a shift to hunting using jaws and heads instead of claws.
Charlie Roger Scherer, a PhD student at UCL Earth Sciences, said: “Trying to pull and grab at a 100ft-long sauropod with your claws is not ideal.
“Attacking and holding on with the jaws might have been more effective.
“It is highly likely that strongly-built skulls came before shorter forelimbs. It would not make evolutionary sense for it to occur the other way round, and for these predators to give up their attack mechanism without having a back-up.”
‘Use it or lose it’
Therapods, a major branch of dinosaurs with three toes, found themselves in an “evolutionary arms race” to develop better methods of subduing the large beasts, losing what they did not need along the way, the experts believe.
Mr Scherer added: “It’s a case of ‘Use it or lose it’ – the arms are no longer useful and reduce in size over time.”