It's a physical mismatch that's long puzzled paleontologists: Tyrannosaurus rex, terror of the Cretaceous Period, empowered with a giant head and ferocious jaws, yet also stuck with tiny, seemingly useless arms. Per National Geographic, scientists' speculation on the arms has included using them to hang onto prey, as leverage when getting off the ground, or for pulling mates closer during sex; the general consensus is that whatever they were used for, they were vestigial appendages. But Steven Stanley of the University of Hawaii at Manoa has come up with a different theory. In research presented at last week's meeting of the Geological Society of America, Stanley posits that the dinosaur's arms were used for "vicious slashing," and he offers six points to support his argument, including that the arms' length would have been ideal for close-quarter cuts.
Also, the T. rex's "huge … sickle-shaped claws" would've done some serious damage—specifically, being able to "inflict four gashes [3 feet] or more long and [more than an inch] deep within a few seconds," capable of repeating this "multiple times in rapid succession." Other scientists are skeptical the creature would have held such power in those short arms, noting that when the T. rex was near enough to actually use them, that would have rendered its most deadly tool—its jaws—useless at such close range. Some are still sticking with the sex theory, though Stanley notes the claws would have made such an amorous embrace somewhat perilous. He believes that as the dinosaur evolved, its arms initially atrophied as its jaws became more vital to its survival, but that "natural selection" eventually gave the arms something useful to do. (T. rex apparently couldn't run very fast.)