The white rhinoceros is the biggest galloping mammal alive today, typically weighing in at around three tons. If it were to stumble while cruising along at 16 miles per hour, it would belly flop to the ground with a force of 12 tons and probably suffer a substantial boo-boo or two. The fate of a tripping Tyrannosaurus rex, though, could easily have been far worse. It was roughly twice as heavy as a white rhino, and it had the added disadvantage of being a biped: if one foot tripped and it couldn’t bring the other one forward fast enough, the beast would have come crashing down, without forelimbs strong enough to break its fall, and with its face, starting from 12 feet up, having plenty of time to gain speed before impact.
Paleontologist James Farlow and physicist John Robinson of Indiana University found themselves captivated by this image while studying a model of a T. rex made from a nearly complete skeleton at the Museum of the Rockies. They began to wonder whether the beast could have survived a fall.
Farlow and Robinson calculate that a 6.5-ton T. rex charging along at 45 mph--the top speed attributed to it by some researchers--would have landed on its belly with a force of almost 80,000 pounds and received a blow to the skull of more than 30,000 pounds. Even if that didn’t squash its organs and its skull, the dinosaur would then have skidded on its belly for almost 50 feet, with its torso finally overtaking its head and snapping its neck.
The Indiana researchers don’t believe T. rex ever got close to 45 mph. Their examination of the tyrannosaur’s thighbone and hip joint suggests that its bones would only have been strong enough to withstand the normal stresses of running at speeds of up to 25 mph, roughly matching Carl Lewis. But they argue that T. rex, knowing that any fall might kill it, would probably not have dared much more than 15 mph. Part of what makes running such a hazardous thing for the beast is simply that if it’s going that fast, it has a greater chance of falling, says Farlow. Even if it could, there are consequences that it might not want to deal with.