Maiasaura was large, attaining an adult length of about 9 metres (30 ft) and had the typical hadrosaurid flat beak and a thick nose. It had a small, spiky crest in front of its eyes. The crest may have been used in headbutting contests between males during the breeding season.
This dinosaur was herbivorous. It walked both on two (bipedal) or four (quadrupedal) legs and appeared to have no defense against predators, except, perhaps, its heavy muscular tail and its herd behaviour. These herds were extremely large and could have comprised as many as 10,000 individuals. Maiasaura lived in an inland habitat.
Maiasaura was discovered by Laurie Trexler and described by dinosaur paleontologist Jack Horner and Robert Makela. He named the dinosaur after Marion Brandvold's discovery of a nest with remains of eggshells and babies too large to be hatchlings. These discoveries led to others, and the area became known as "Egg Mountain", in rocks of the Two Medicine Formation near Choteau in western Montana. This was the first proof of giant dinosaurs raising and feeding their young. Over 200 specimens, in all age ranges, have been found. The announcement of Maiasaura's discovery attracted renewed scientific interest to the Two Medicine Formation and many other new kinds of dinosaurs were discovered as a result of the increased attention. Choteau Maiasaura remains are found in higher strata than their Two Medicine River counterparts.