These dinosaurs are members of the hadrosaurid family, sometimes called “duck-billed” dinosaurs. They are large animals, being 40 to 50 feet in length, and are able to go on four feet or two. Edmontosaurs are plant eaters who prefer swamp-lands and floodplains. They are shy creatures, prone to fleeing if possible; their only effective attack is to lash out with their long, heavy tails.