Speedy Hunters?
How fast were big predators like T. rex and Tarbosaurus? Scientists have debated this for many years. One way they try to answer this question is with biomechanics, the study of how animals move their bodies. Scientists examine fossils and observe the muscles and movement of living species. When they wanted to understand how the massive, two-legged T. rex moved, they used fossil information to build an accurate scale model of its skeleton. They noticed that unlike four-legged dinosaurs, bipedal dinosaurs carried their entire weight on one leg, as humans do. In addition, their long tails must have helped balance them.

Scientists also compared the movement of T. rex to a modern-day relative, the ostrich. The ostrich, which has a similar skeleton, is quite fast-reaching speeds of up to 45 miles per hour. However, the T. rex was also nearly 40 times heavier. With this in mind, scientists estimate that T. rex would have run only about 10 miles per hour.