UC paleontologist speculates why T. Rex arms were so small

He would usually go down the list of possibilities: for mating, for holding or stabbing prey, for tipping over a Triceratops. Eventually, he would get to “No one knows.”

But he also suspected scientists were coming at it from the wrong angle. Why would the arms of a ferocious predator shrink over time, through evolution?

Because they needed to be smaller, to help the whole animal’s chances of survival, he postulated. What if it wasn’t about what the arms did, but what they didn’t do?

According to a news release from UC Berkeley, Padian floats his new hypothesis in a paper published in the current issue of the journal “Acta Palaeontologia Polonica.”

The university said the idea goes like this: “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.

“What if several adult tyrannosaurs converged on a carcass? You have a bunch of massive skulls, with incredibly powerful jaws and teeth, ripping and chomping down flesh and bone right next to you. What if your friend there thinks you’re getting a little too close? They might warn you away by severing your arm,” said Padian, a distinguished emeritus professor of integrative biology at the UC Berkeley and a curator at the UC Museum of Paleontology, in a statement.