No-one has ever seen a dinosaur in action. However, the bones and the joints of fossilized skeletons can give us clues as to how the animals moved. Marks on the bones can show where the muscles were attached. The articulation of the bones (the way the bones move in relation to one another) shows how the limbs were flexed and how far they could reach. The size of the feet shows whether a dinosaur was a slow plodder (big, solid feet) or a fast runner (lightweight feet). Above all, scientists can find out more about dinosaurs by comparing what they know with the anatomy and lifestyle of modern animals.
The modern equivalent of a running dinosaur would be one of today’s flightless birds, such as an ostrich or a rhea. Like a dinosaur, these keep their bodies horizontal and their heads high. The long legs, with their muscular thighs and their lightweight feet, are very similar to those of their theropod ancestors.
The shape of the hip bones suggests that Tyrannosaurus would have rested flat on its belly. While it was in this position, the weight of the hips would have been carried by the broad “boot” at the end of the pubis bone. How, then, did the dinosaur manage to stand up? It is possible that it used its tiny arms to give itself some leverage.
As Tyrannosaurus rose to its feet by straightening its legs, it would have been in danger of toppling forward and sliding along the ground. The little arms, however, would have gripped the ground and prevented this from happening. If the head was thrown backwards, this would have moved the centre of gravity back towards the hip.
The normal stance of a Tyrannosaurus was with the body held horizontally, the head pushed forwards, and the tail out at the back to provide balance. Like this, the dinosaur would have been formidable fighting machine propelled by powerful legs, with its main weapons – its teeth – held well forward to attack or defend.