Smithsonian.com

The skeleton of Edmontosaurus. From the Palaeontologia Electronica paper.

I always feel a bit sorry for hadrosaurs. They are sometimes referred to as the “cows of the Cretaceous,” herbivorous dinosaurs that lacked the impressive armor, spikes, and horns of their relatives the ankylosaurs and ceratopsians. This does not mean that hadrosaurs were entirely defenseless against the tyrannosaurs that so often preyed upon them, though. For dinosaurs, the hadrosaurs had a fair turn of speed, and a new study published in the open-access journal Palaeontologia Electronica investigated the ways in which they might have fled their predators.

Hadrosaurs were interesting because unlike most dinosaurs they could be either “2-wheel-drive” or “4-wheel-drive” animals. They were comfortable walking on two legs, but their arms and posture also allowed them to walk on four, and so this left them multiple options for getting around. Out of the various gaits that were hypothetically possible for the dinosaurs, the authors of the new study decided to use computer modeling to see what would happen if a hadrosaur ran on two legs, ran on four legs, or hopped like a kangaroo.

When the scientists made their virtual dinosaur go through each of these gaits they got very different results. It would appear that hadrosaurs would be able to move fastest while hopping, about 17 meters per second. Running on all fours (about 15 meters per second) and on two legs (about 14 meters per second) yielded slower speeds.

Does this mean that hadrosaurs hopped around the Cretaceous like giant kangaroos? Probably not. While they certainly could have hopped, doing so would have put massive strains on their skeletons. The same would be true, albeit to a slightly lesser extent, of running on all fours. If a hadrosaur hopped or galloped as fast as it could, it would put heavy stresses on its bones and therefore be more likely to break them or otherwise injure itself, something that is not very advantageous while running away. According to the authors, the best compromise between speed and reduction of stress on the skeleton was running on two legs. True, the hadrosaurs might not have been able to move as fast, but when you are fleeing a predator the only thing you have to worry about is that you are running faster than they are!