Maiasaura (meaning "good mother lizard") is a large duck-billed dinosaur genus that lived in the area currently covered by the state of Montana in the Upper Cretaceous Period (Campanian), about 74 million years ago.
Maiasauralived in herds and it raised its young in nesting colonies. The nests were made of earth and contained 30 to 40 eggs laid in a circular or spiral pattern. The eggs were about the size of ostrich eggs.
The eggs were incubated by the heat resulting from rotting vegetation placed into the nest by the parents, rather than a parent sitting on the nest. Upon hatching, fossils of baby Maiasaura show that their legs were not fully developed and thus they were incapable of walking. Fossils also show that their teeth were partly worn, which means that the adults brought food to the nest.
The hatchlings grew from a size of 16 inches to 58 inches long in the span of their first year. At this point, or perhaps after another year, the animal left the nest. This high rate of growth may be evidence of warm bloodedness. The hatchlings had different facial proportions from the adults, with larger eyes and a shorter snout. These features are associated with cuteness and are common among animals that are dependant on their parents' for survival during the early stages of life.
In the Two Medicine Formation, Maiasaura lived alongside the tyrannosaurid Daspletosaurus, the oviraptorosaurian Chirostenotes, the troodontid Troodon, the dromaeosaurids Bambiraptor and Saurornitholestes, the enantiornithe bird Avisaurus, the nodosaurid Edmontonia, the ankylosaurid Euoplocephalus, the ceratopsids Achelousaurus, Brachyceratops, Einiosaurus, and Styracosaurus ovatus, the hypsilophodont Orodromeus, and the hadrosaurids Hypacrosaurus stebingeri and Prosaurolophus.