Why T. rex has little arms

Scientists explain short dinosaur arms - 1st June 2026

The arms of a Tyrannosaurus rex seem too small for its body. But scientists may now have the answer to this mystery.

T. rex walked the Earth from 68 to 66 million years ago. It grew up to 13 metres long and four metres tall. But it had arms that were less than a metre long.

Many different reasons were suggested for their small arms. Some people thought that they were for holding down their food. Other people thought that they used them to get the attention of a partner.

Scientists from Cambridge University and University College London have found an interesting connection. They compared 85 different dinosaur species that were all meat eaters.

The scientists found the same pattern in all five different groups of dinosaurs. The dinosaurs which ate the largest animals had bigger heads and smaller arms.

Strong, heavy heads were better for killing animals than big arms. Over time, these different species all developed stronger heads and smaller arms.

The dinosaurs with the strongest heads had much smaller arms. It's a "use it or lose it" situation, says scientist Charlie Roger Scherer.

They still don't know what they used these small arms for. But Scherer hopes they can find that out "with a bit more work."