T. rex's Tiny Arms Explained by Powerful Jaws, Study Finds

A study published May 20 in Proceedings of the Royal Society B suggests that Tyrannosaurus rex and other theropod dinosaurs evolved tiny forelimbs due to their increasingly powerful skulls and jaws. Researchers led by Elizabeth Steell of the University of Cambridge and Charlie Scherer of University College London analyzed data from 85 non-avian theropod species, calculating skull strength and forelimb-to-skull ratios. T. rex, which lived 66–68 million years ago and grew up to 40 feet long, had arms about three feet long—less than one-third the length of its legs. The study found a strong correlation between cranial strength and reduced forelimb size across tyrannosaurids, abelisaurids, carcharodontosaurids, ceratosaurids, and megalosaurids, with the latter two groups newly identified as following this trend. The evolutionary driver may have been larger prey, such as sauropods, forcing predators to rely on head-first attacks. Andre Rowe of the University of Bristol noted the arms may not have been entirely useless. The research confirms long-held suspicions about the function of these iconic limbs.