Answers are coming from an area of science called biomechanics. This approach applies principles of physics and engineering to biological movement; it lets scientists study animals--including humans--as if they were machines.
Not all dinosaurs were big, but the biggest ones outweighed anything that ever walked on Earth. And exactly how they walked on Earth has puzzled the curious for nearly 200 years.
Big animals alive today have a lot in common. They are heavy. They have few predators. And they tend to move slowly. But have big animals always behaved this way?
The bigger an animal gets, the harder its muscles must work just to support its weight. As a result, enormously large animals, including T. rex, have more trouble getting around than you might imagine.
Current research suggests that T. rex would have moved at the rough equivalent of 11 to 16 kilometers (seven to ten miles) per hour. This is much slower than many previous estimates, and it's certainly less speedy than most Hollywood versions of the great Cretaceous carnivore.
Young animals are smaller than grown ones: that's one way we tell them apart. But the age at which juveniles achieve full size varies from species to species.