Scientists have made significant strides in understanding the small arms of Tyrannosaurus rex, a feature that has puzzled researchers for over a century. A study published on May 20 in *Proceedings of the Royal Society B* analyzed 85 dinosaur species and concluded that the diminutive forelimbs are a result of an evolutionary trade-off for stronger skulls, which are crucial for hunting larger prey. Lead author Charlie Roger Scherer from University College London noted that as dinosaurs evolved stronger skulls, they invested less energy in maintaining their forelimbs, leading to their reduction in size. This trend was observed across five different dinosaur groups over approximately 180 million years, suggesting that shrinking arms were not merely a fluke but a common evolutionary adaptation. The research highlights how large predatory dinosaurs prioritized bite force and hunting efficiency over limb size, with T. rex exemplifying this pattern. The study opens avenues for further research into the specific functions of these small arms, which, while not entirely useless, remain a mystery.