Parasaurolophus cyrtocristatus skeleton, Field Museum.
A hadrosaur is any of various herbivorous dinosaurs of the family Hadrosauridae, whose most distinguishing feature was a duck-like bill. The hadrosaurs flourished in the upper Cretaceous Period. (Greek hadros: "thick, heavy".)
It used to be thought that the hadrosaurs had webbed feet and were therefore amphibious. However, this was a misconception arising from the fact that one of the early hadrosaur fossil finds had preserved skin impressions on the feet that made them appear to be webbed; it was later determined that these impressions were actually due to desiccated foot pads such as are seen on dried camel feet. [Thanks to Joseph Daniel for this piece of information.]