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New study uncovers theory on why the T. rex had tiny arms

Researchers found reduced forelimbs were strongly linked to more robust skulls across 61 theropod species, suggesting jaws replaced arms as the main attack weapon.

  • New research published in the Proceedings of the Royal Society B: Biological Sciences links shrinking arms in tyrannosaurs to the evolution of massive, robust skulls, led by vertebrate paleontologist Charlie Roger Scherer at University College London.
  • As prey like 100-foot sauropods grew larger, dinosaurs relied less on grasping claws and more on powerful jaws, with Scherer noting that "attacking and holding on with the jaws might have been more effective."
  • Examining 61 theropod species, the team developed a new scoring system for skull robustness based on bite force and bone connectivity, finding a strong correlation between shorter forelimbs and skull strength across five separate theropod families.
  • Although T. Rex arms could still curl more than 100 kilograms, they became less useful over time, with Scherer describing the evolutionary trade-off as a case of "use it or lose it."
  • Separate research published in PeerJ suggests T. Rex took up to 40 years to reach adult size, with Jack Horner of Chapman University noting this long growth phase allowed younger dinosaurs to fill diverse ecological roles.
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Madrid. According to a new study led by researchers from UCL (University College London) and Cambridge University in the United Kingdom, the evolution of tiny arms in several groups of carnivorous dinosaurs was probably driven by the development of strong and powerful heads, which were used to attack prey.

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Why the T-Rex had tiny arms

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The Telegraph broke the news in London, United Kingdom on Wednesday, May 20, 2026.
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