MAIASAURA

genus of duck-billed dinosaurs (hadrosaurs) found as fossils in Late Cretaceous rocks (97.5 to 66.4 million years old) of North America. Maiasaura were bipedal, slow-moving herbivores, some 8 m (26 feet) in length; it is believed that they were migratory. In 1978 a Maiasaura nesting site was discovered in the Two Medicine Formation near Choteau, Montana, U.S. The remains of an adult Maiasaura were found in close association with a nest of juvenile dinosaurs, each about 1 m (3.3 feet) long. Nests of hatchlings (about 0.5 m [1.6 feet] long) and nests with clutches of eggs, as well as many broken eggshells, were found nearby. These associations suggest that the nests and young dinosaurs are of the Maiasaura kind, and have led to the theory that duck-billed dinosaurs cared for their young. The site also demonstrates that Maiasaura were social animals, nesting in groups; they probably also returned to the same site year after year.