Not everything about Tyrannosaurus rex was fierce, however. This dinosaur had unexpectedly puny arms, and the function of these little limbs is a source of debate among scientists. Some believe the animal’s arms were an evolutionary leftover—like the pelvic bones of a snake—or served non-predatory purposes like helping it grip a mate. Others argue that T. rex’s arms may have been adapted for “vicious slashing” at close quarters, given their ability to inflict deep wounds with four-inch claws.And while they had strong thighs, these dinosaurs were not speedy.

They could only walk briskly at up to 12 miles an hour—likely not fast enough to chase a speeding Jeep, as depicted in the movie Jurassic Park. Using biomechanical models, scientists have theorized that if these heavy animals moved any faster, they would have shattered the bones in their feet.