| Named By: | Jack Horner & Robert Makela in 1979 |
| Time Period: | Late Cretaceous, 76.7 Ma |
| Location: | USA - Montana - Two Medicine Formation |
| Size: | Around 9 meters long |
| Diet: | Herbivore |
| Fossil(s): | Remains of over 200 individuals from newly hatched juveniles to adults including nests |
| Classification: | | Chordata | Reptilia | Dinosauria | Ornithischia | Ornithopoda | Hadrosauridae | Saurolophinae | Brachylophosaurini | |
Maiasaura (from the Greek "maia" and the feminine form of Latin saurus, meaning "good mother reptile" or "good mother lizard" ) is a large herbivorous hadrosaurid ("duck-billed") dinosaur genus that lived in the area currently covered by the state of Montana in the Upper Cretaceous Period (mid to late Campanian), about 76.7 million years ago.
The first fossils of Maiasaura were discovered in 1978. In 1979, the genus was named. The name refers to the find of nests with eggs, embryos and young animals, in a nesting colony. These showed that Maiasaura fed its young while they were in the nest, the first time such evidence was obtained for a dinosaur. Hundreds of bones of Maiasaura have been dug up.
Maiasaura was about nine metres long. Young animals walked on their hind legs, adults on all fours. Maiasaura was probably closely related to Brachylophosaurus.