Maiasaura were dinosaurs. Duck-billed hadrosaurs to be more precise. They were reasonably large, for a dinosaur: weighing in at 3-4 tonnes all up. Somewhat sentimentally named the "Good Mother Lizard" because the first finds included nests full of fossilized babies indicating a high level of socialisation.
The babies that didn't get fossilized grew up fast! In only a year, they grew from around 33cm to 3 metres (from 1ft to 10ft, if you use imperial measures). Fully grown they were around 10 metres (30 feet) long and 3-4 metres (10-13 feet) tall.
Somewhat like sharks, maiasaura continuously grew new teeth to replace old ones as they wore out. Unlike sharks, however, the growing teeth popped up from directly underneath the worn out ones when they fell out.
That jaw was just fantastic for chewing things too. Sort of like two plates of really rough sandpaper just grinding away at anything that got too close. Well, anything that didn't move too fast anyway, since they were vegetarians. Oh alright, herbivores, if you want the technical term.
The strangest thing about the maiasaur has to be that it is the "Official State Fossil" of Montana, which is pretty much its old stomping grounds.
Other hadrosaurid dinosaurs include: Hadrosaurus, Hypacosaurus, Corythosaurus, Edmontosaurus, Kritosaurus, Lambeosaurus, Parasaurolophus, Prosaurolophus and Saurolophus.