Study Links 5 Theropod Lineages' Tiny Arms to Bigger Skulls as Prey Grew Larger
Updated
Updated · Cyprus Mail · Jun 7
Study Links 5 Theropod Lineages' Tiny Arms to Bigger Skulls as Prey Grew Larger
3 articles · Updated · Cyprus Mail · Jun 7
Summary
Five theropod lineages independently evolved robust skulls before their forelimbs shrank, according to a new study tracing the pattern behind T. rex-style tiny arms.
Larger plant-eating dinosaurs appear to have driven the shift: as prey size surged from the Triassic onward, some predators relied more on crushing jaws and less on arms for hunting.
Researchers built a new skull-robustness measure using skull size, bite force, tooth shape and bone fusion; Tyrannosaurus ranked highest, followed by South America's Tyrannotitan.
The pattern showed up in tyrannosaurs, carcharodontosaurs, megalosaurs, ceratosaurs and abelisaurs, with one early example—Eoabelisaurus—dating to about 170 million years ago.
Some large theropods such as Spinosaurus and Megaraptor kept powerful arms, while the study says T. rex's reduced two-fingered limbs may have persisted because genes tied to arm development also serve other functions.