The famously small arms of the Tyrannosaurus Rex may have a clear evolutionary explanation: they shrank as the dinosaur's head and jaws grew larger and more powerful. Researchers studied 82 theropod species and found a strong correlation between the development of robust skulls and jaws and the reduction in arm size.
This suggests that theropods, including T. Rex, increasingly relied on their heads and jaws as their primary weapons for attacking and subduing prey. Over time, this evolutionary shift led to the 'use it or lose it' phenomenon, where the arms became vestigial and significantly reduced in size. This pattern was observed across various theropod species, not just the T. Rex, and was linked to cranial development rather than overall body size.
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