Why did T. rex have such small arms? Scientists finally SOLVE mystery

Tyrannosaurus rex had very small forelimbs, about three feet long, and scientists have long sought an explanation. Research from University College London proposes that forelimb reduction was driven by the evolution of strong, powerful heads. Other giant theropods also developed relatively small forelimbs, including Carnotaurus with even smaller arms. The study found a strong relationship between short arms and large, powerfully built heads, suggesting a shift in attack strategy from arms to the head. The “use it or lose it” idea implies arms became less useful and reduced over time. Analysis of 82 theropod species showed forelimb shortening across multiple groups and found it was not primarily linked to overall body size.

"Everyone knows the T. rex had tiny arms but other giant theropod dinosaurs also evolved relatively small forelimbs. The Carnotaurus had ridiculously tiny arms, smaller than the T.rex. We sought to understand what was driving this change and found a strong relationship between short arms and large, powerfully built heads. The head took over from the arms as the method of attack."

"It's a case of "use it or lose it" - the arms are no longer useful and reduce in size over time. T. rex first appeared in the Late Jurassic period, and reached its peak in the Late Cretaceous before becoming extinct about 65.5 million years ago. Previous studies have shown that the species - also known as the 'King of the Dinosaurs' - had tiny arms."

"To get to the bottom of it, the researchers analysed data on 82 species of theropod - two-legged, mainly meat-eating dinosaurs. Their analysis revealed that shortening of the forelimbs occurred across five groups -tyrannosaurids, abelisaurids, carcharodontosaurids, megalosaurids and ceratosaurids. While the researchers initially expected that smaller arms would be linked to larger overall body size, surprisingly this wasn't the case."

"Instead, tiny arms were found to be closely linked to the development of powerful skulls and jaws. The secondary importance of overall body size was highlighted by the fact that some theropo"

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