Science: Dinosaurs: Why did T. rex have such tiny arms?

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Tyrannosaurus rex and many of its theropod cousins had large bodies but tiny arms. What gives?

Tyrannosaurus rex had a huge head and rear legs, but puny arms. There are likely a number of reasons for that.

Tyrannosaurus rex was a vicious hunter with the strongest bite of any animal ever to walk on land. The beast prowled the late Cretaceous wilderness more than 66 million years ago, looking for a Triceratops or Edmontosaurus to munch on.

The only thing not menacing about the king of the tyrant lizards was its tiny arms. T. rex wasn’t the only dinosaur with small arms compared with the rest of its body; many of its theropod cousins — a group of bipedal, mostly meat-eating dinosaurs — shared this trait. But why did many theropods evolve such stubby arms?

Scientists have proposed a few possible explanations.

A 2021 study published in the journal Acta Paleontologica Polonica suggested that bone-crushing theropods such as T. rex evolved small arms so they wouldn’t bite each other’s arms off when they fed.

Paleontological evidence suggests that these animals devoured their prey as a pack, so perhaps they evolved the little limbs to avoid accidental arm-ripping as a throng of theropods descended on a tackled Triceratops, the study author proposed.

Right now, however, this is just a hypothesis. "It’s a nice story," said John Hutchinson, a biologist at the University of London’s Royal Veterinary College who wasn’t involved in the study. "But I think, ultimately, we don’t really know."

Hutchinson, who studies the biomechanics of movement in large terrestrial animals — both living and extinct — looks at dinosaur forelimb evolution a different way: In the evolution of theropods, "the arms didn’t really get shorter, but the legs got longer," he said.

Source: https://www.livescience.com/why-tyrannosaurus-rex-theropod-dinosaurs-small-arms?utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D