Study Links T. rex’s 3-Foot Arms to Skull Growth Across 85 Dinosaur Species

5 articles · Updated · CNN · May 25

A May 20 study in Proceedings of the Royal Society B found T. rex’s tiny forelimbs were likely an evolutionary trade-off, with resources diverted to building larger, stronger skulls.
Researchers analyzed 85 dinosaur species and created a skull-strength scale using bone structure, size and bite force; T. rex ranked highest, supporting the idea that head power replaced arm function in hunting.
The pattern appeared in five carnivorous dinosaur groups—not just tyrannosaurids—suggesting small arms evolved repeatedly over roughly 180 million years rather than as a one-off quirk.
Outside experts said the findings fit a broader energy-allocation logic: giant predators benefited more from investing in jaws and bite force, while herbivores kept longer forelimbs for feeding and defense.
The study does not claim the arms were useless, but it strengthens a leading explanation for one of paleontology’s longest-running debates over why some top predators evolved oversized heads and reduced limbs.

If T. rex's arms never shrank, would a weaker bite have cost it the title 'king of the dinosaurs'?

Could the genes that shrank T. rex's arms for a stronger bite still exist in modern birds today?