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Study: T. rex Arms Shrank as Skulls Became the Main Weapon

A new skull-robustness metric links powerful jaws to forelimb loss.

Overview

  • This week a team from University College London and the University of Cambridge published a comparative study in Proceedings of the Royal Society B that analysed morphological data from 82 carnivorous theropod species.
  • The researchers introduced a quantitative skull-robustness metric and found a clear pattern: species with more robust skulls and stronger bite-related features tended to have more reduced forelimbs.
  • By that metric Tyrannosaurus rex scored highest for skull robustness, followed by Tyrannotitan, supporting the idea that jaw-focused predation drove arm reduction in some giant predators.
  • The authors argue that hunting very large sauropod prey made grappling with claws impractical, so selection favoured bite-and-hold strategies that made forelimbs progressively redundant.
  • The study emphasises clade-specific developmental routes to limb loss and notable exceptions such as long-armed spinosaurids, and it presents a testable morphometric hypothesis rather than definitive behavioral proof.