Why Did T. Rex Have Such Tiny Arms? A New Study Has a Theory

For decades, scientists have puzzled over one of paleontology's most entertaining questions: why did Tyrannosaurus rex, arguably the most fearsome predator to ever walk the earth, have such uselessly small arms?

A new study thinks it finally has an answer, and it comes down to a biological trade-off. Researchers say the T. rex evolved an extraordinarily powerful skull, and because evolution tends to refine one feature at a time, that development came at the expense of upper body strength. In short, the arms lost out.

The logic, researchers say, is straightforward. When you can kill nearly anything by driving your skull into it, you simply don't need strong arms. The T. rex's head did the heavy lifting, quite literally, making the rest of its upper body largely redundant from a survival standpoint.

The hypothesis was published last week in the journal Proceedings of the Royal Society B.