Story perspectives

Theropods Grew Massive Skulls, Shrunk Arms — 5 Lineages Converge

6/21/2026

Summary

Story summary

University College London researchers reported that giant theropods evolved tiny arms as their skulls grew, based on 82 fossils.
A second study of 85 species confirmed the inverse skull-arm correlation and showed at least five predator lineages independently adopted the huge-head, tiny-arms plan.
They cite a ‘use it or lose it’ trade-off favoring larger jaws, noting T. rex’s reduced arms stayed muscular and may have had secondary uses unlike spinosaurs.

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Story summary

University College London researchers reported that giant theropods evolved tiny arms as their skulls grew, based on 82 fossils.
A second study of 85 species confirmed the inverse skull-arm correlation and showed at least five predator lineages independently adopted the huge-head, tiny-arms plan.
They cite a ‘use it or lose it’ trade-off favoring larger jaws, noting T. rex’s reduced arms stayed muscular and may have had secondary uses unlike spinosaurs.