Maiasaura, meaning “good mother lizard”, is a genus of dinosaur from the Campanian age of the Upper Cretaceous Period (74 million years ago). It lived in what is now the state of Montana in the United States. It was discovered by paleontologist Jack Horner, whom was a paleontology advisor for the Jurassic Park movies. It was also co-discovered by Robert Makela. The dinosaur was named after finding a series of nests with egg and hatchling remains at Egg Mountain, in rocks of the Two Medicine Formation in Montana. This became the first evidence of giant dinosaurs raising and feeding their young. Over 200 specimens have been found.

Maiasaura was about 30 feet in length and has a flat beak and thick nose typical of hadrosaurids. It had a small, spiky crest in front of its eyes. The crest may have been used for head butting between males during breeding seasons. This was a herbivorous dinosaur that walked on either two or four feet. It had no defense against predators, except for its heavy muscular tail and its herding behavior. Herds were extremely large and may have consisted of as many as 10,000 individuals.

Colonies of nests were packed close together, like that of modern seabirds. Gaps between nests were about 23 feet apart, less than the length of an adult animal. The nests contained 30 to 40 eggs each laid in circular or spiral patterns. The eggs were roughly the same size as an ostrich egg. The eggs were incubated by the heat resulting from rotting vegetation placed in the nest by the parents. The parents did not incubate them by sitting on them as most modern birds do. It is known by the evidence of fossil remains, that newly hatched babies did not have fully developed legs and were not capable of walking immediately. Their teeth appeared worn, which means that food was brought to the nest by the parents or other adults. The young grew to about 58 inches in the first year, and after a second year, would have left the nest. This high rate of growth may be evidence of warm bloodedness.

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