T. rex’s short arms may have lowered risk of bites during feeding frenzies

April 4, 2022

Over the two decades paleontologist Kevin Padian taught a freshman seminar called The Age of Dinosaurs, one question asked frequently by undergraduates stuck with him: Why are the arms of Tyrannosaurus rex so ridiculously short?

He would usually list a range of paleontologists’ proposed hypotheses — for mating, for holding or stabbing prey, for tipping over a Triceratops — but his students, usually staring a lifesize replica in the face, remained dubious. Padian’s usual answer was, “No one knows.” But he also suspected that scholars who had proposed a solution to the conundrum came at it from the wrong perspective.

Rather than asking what the T. rex’s short arms evolved to do, Padian said, the question should be what benefit those arms were for the whole animal.

In a new paper appearing in the current issue of the journal Acta Palaeontologia Polonica, Padian floats a new hypothesis: The T. rex’s arms shrank in length to prevent accidental or intentional amputation when a pack of T. rexes descended on a carcass with their massive heads and bone-crushing teeth. A 45-foot-long T. rex, for example, might have had a 5-foot-long skull, but arms only 3 feet long — the equivalent of a 6-foot human with 5-inch arms.

Berkeley News