Study: T. rex's short arms may have reduced biting risk of hunting in packs

The Tyrannosaurus rex's arms may have evolved to become extremely short to lower the risk of bites while feeding in packs, a new study says.

A 45-foot-long T. rex may have 3-feet long arms--the equivalent of a 6-foot human with 5-inch arms, study author Kevin Padian, emeritus professor at the University of California, Berkeley, and a curator of the UC Museum of Paleontology, noted in a statement.

Padian, who taught a freshman seminar on dinosaurs for over two decades, said in the statement students often asked him why the T. rex's arms were so short, and he would list a range of proposed hypotheses, from mating to stabbing prey, but they remained skeptical.

He added that he kept his students question in mind as he conducted the study, which appears in the current issue of the journal Acta Palaeontologica Polonica.

Padian also noted that predecessors or tyrannosaurids had longer arms.

He found in the study that previous hypotheses couldn't explain why the arms had become short because "in all cases a larger limb would have suited the function better," but another reason came to him after paleontologists unearthed evidence that some hunted in packs.

"What if several adult tyrannosaurs converged on a carcass?," he asked in his statement. "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."

"So, it could be a benefit to reduce the forelimbs, since you're not using them in predation anyway," he added, noting that several bite wounds could also cause infection, hemorrhaging and eventual death.

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