Study Traces T. rex Small Arms to 170 Million Years of Skull-Driven Evolution

6 articles · Updated · Reuters · May 29

Five theropod lineages independently evolved bigger, more robust skulls before their forelimbs shrank, according to a new study explaining the T. rex body plan.
170 million years ago, early examples such as Eoabelisaurus were already showing the pattern as plant-eating prey grew larger and predators relied more on jaws than arms to hunt.
1.5-meter skulls and extreme bite force made Tyrannosaurus the top scorer in the researchers' new skull-robustness measure, with a close link found between stronger heads and reduced arms.
Some large theropods, including Spinosaurus and Megaraptor, kept long, powerful arms, suggesting the tradeoff was not universal and reflected different hunting strategies.
The work suggests tiny arms may have persisted not because they were useful, but because genes tied to limb development also served other functions.

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