Scientists may have finally solved the riddle of Tyrannosaurus rex’s small arms, which have always stood out as the oddest feature in the mightiest of dinosaurs, prompting jokes and a century-plus debate on their purpose and evolutionary history.At about 3 feet long, the arms of T. rex were less than a third of the length of the dinosaur’s legs and looked noticeably disproportionate in a body that could span more than 40 feet in larger adults.T. rex was one of many meat-eating dinosaurs with puny arms, and over the years scientists have come up with theories for the forelimbs’ function, including holding or pinning down prey and impressing potential mates during courtship. More recent studies have suggested that the arms became smaller to reduce the risk of being bitten during feeding frenzies, while a longstanding theory is that they are simply vestigial — they had no practical purpose and therefore shrank. But a consensus is lacking.AdvertisementAdvertisementNow, a new study published May 20 in the journal Proceedings of the Royal Society B aims to settle the debate once and for all. Based on an analysis of 85 species of dinosaurs, the study concluded that tiny arms were an evolutionary trade-off caused by another body part becoming ever larger and taking up resources — the skull.“If you’re a dinosaur with a very strongly put together skull, chances are you’re going to have very small forelimbs,” said Charlie Roger Scherer, a doctoral student in the department of Earth sciences at University College London and the study’s lead author. “And it doesn’t really matter how big you are — you could be 1 ton in weight, or 10 tons in weight. If you have a strong skull, you’re going to have relatively small arms.”The large skull of T. rex might be the reason why the forelimbs shrunk to their smal …
