Overview
- A peer‑reviewed paper in Proceedings of the Royal Society B introduces a new skull‑robusticity metric that combines skull size, bite‑force estimates, tooth form and cranial bone fusion to quantify head strength across about 82–85 theropod species.
- The analysis shows a strong statistical association between increased skull robustness and reduced forelimb size, with Tyrannosaurus rex scoring highest on the new scale for bone‑crushing head power.
- The skull‑first, arm‑reduction pattern evolved independently in at least five theropod lineages, indicating repeated changes in hunting strategy among separate groups of large predators.
- The pattern is not universal because some large theropods such as Spinosaurus and Megaraptor retained large, functional arms and small theropods including the bird lineage kept useful forelimbs, showing ecological and functional variation.
- Authors stress the results are correlational and call for targeted biomechanical modelling and developmental and genetic studies to test causation and to explain why tiny arms persisted, with genetic pleiotropy offered as one possible explanation.