At least five groups of theropods all gradually relied more on their jaws than front claws. Credit: Orla via Shutterstock

Get the Popular Science daily newsletter💡

Breakthroughs, discoveries, and DIY tips sent six days a week.

By signing up, you confirm you are 16+, will receive newsletters and promotional content and agree to our Terms of Use and acknowledge the data practices in our Privacy Policy . You may unsubscribe at any time.

Tyrannosaurus rex is iconic for its ferocity and big teeth, as well as those teeny-tiny arms. The Cretaceous Period apex predator wasn’t the only carnivore with underdeveloped forelimbs, however. At least five groups of two-legged, mostly meat-eating theropod dinosaurs experienced a shortening of the upper arms over the course of their evolutionary journey. But why did they have such comically small claws?…