Palaeontology

Why did giant theropod dinosaurs like T. rex have such tiny arms ?

By T.K. Randall
May 20, 2026

Image: Tyrannosaurus Rex Holotype
Credit: ScottRobertAnselmo / CC BY-SA 3.0 (adapted) Tyrannosaurus rex was an undeniably ferocious and highly effective apex predator, yet despite its huge head and massive, razor-sharp teeth, its arms were positively tiny.

This phenomenon isn't restricted to just one species either, as other types of large theropod dinosaur also had small arms - so what was the reason ?

Now, a new study headed up by researchers from University College London and Cambridge University has identified what is thought to be the key reason for this.

The researchers found that the development of smaller arms seemed to be directly related to the development of larger heads and more powerful jaws.

In other words, as their jaws became larger, their arms became smaller.Scientists now believe that this may have been a result of plant-eating dinosaurs (the main food source of large carnivores) becoming larger, making large jaws - as oppose to claws - the most effective way to take down prey.

"The head took over from the arms as the method of attack," said lead author Charlie Roger Scherer.

"These adaptations often occurred in areas with gigantic prey."

"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."

Source: Phys.org

Tags: Dinosaurs