Wild New Paper Suggests T. Rex Had Short Arms So Friends Wouldn't Bite Them Off

The tiny arms of the rex have been the subject of a lot of jokes. It is hard to work out evolutionary questions from a pile of 66 million-year-old bones, but we have various hypotheses: perhaps its arms were vicious slashing machines or a way to help grasp on during sex.

The hypothesis that the dinosaurs evolved short arms to lower the risk of accidental bites by other T. rex is presented in a new paper. Short arms are less likely to be eaten by friends.

What if adult tyrannosaurs converge on a carcass? You have a bunch of huge skulls, with powerful jaws and teeth, right next to you. What if your friend thinks you are getting too close? Kevin Padian, an author of the new paper, says that they might warn you away by severing your arm.

Reducing the forelimbs could be a benefit since you are not using them in predatory activity.

Thanks to fossil finds of skin and feathers, paleontologists are able to make assumptions about what dinosaurs did because of how the bones are placed, or footprints that provide more information about their habits.

Complex evolutionary questions are difficult to determine even for species with access to the genomes of their ancestors. It is difficult to figure out what an animal like T. rex is.

When compared to other animals, the T. rex laugh arms are even more ludicrous. Imagine a T. rex that is 45 feet long. They might have a long skull, but their arms are only a meter long. This is the same as a 6-foot human with 5 inch arms.

Padian took measurements of a mostly complete fossil specimen to try and figure out if the friend arm biting hypothesis had legs. He suggests that the sexual aid and slashing arms hypothesis are unlikely, as T. rex arms are too small and weak to be used.

It could have been better to have tiny arms to get them out of the way for group feeding.

Long arms, especially in their natural, somewhat anteriorly extended orientation, would have brought them into the ambit of the deadliest jaws ever recorded on land. Padian explains in his paper that the danger of wounds, amputations, infections, disease and ultimate death would have been a force for reduction.

The reduction of forelimb size was a secondary function of selection. We shouldn't look forFunctionality in these reduced limbs, but for how that reduction served a larger purpose.

Like the other suggestions, this is a hypothesis. Padian suggests that other researchers might be able to test it by finding less bite marks on their arm bones than on other parts of their body.

He wanted to establish that the prevailing functional ideas don't work.

That gets us back to square one. We can think about social organization, feeding behavior and ecological factors apart from mechanical considerations.

The research has been published.