Study of 85 Theropods Links Tiny Arms to Stronger Skulls in 5 Dinosaur Lineages

4 articles · Updated · New Scientist · May 19

Data from 85 theropod species showed dinosaurs with more durable skulls tended to have proportionally smaller forelimbs, offering a broad explanation for why predators like T. rex evolved tiny arms.
The analysis found the pattern across the theropod family tree, suggesting massive heads became the main weapon for subduing increasingly large prey and made strong grappling arms less necessary.
Five lineages independently followed that head-arm trade-off—tyrannosaurids, abelisaurids, carcharodontosaurids, ceratosaurids and megalosaurids—with the last two not previously recognized in this pattern.
Researchers argue the shift reflects an energy trade-off: maintaining both a huge, powerful skull and strong forelimbs would be costly, while some other giant predators instead kept long arms and evolved slimmer skulls.

Why did some giant predators evolve huge arms while T. rex’s vanished?

How did the same ancestral arms become T. rex's nubs and a bird's powerful wings?