Maiasaura

Maiasaura (meaning "good mother lizard") is an extinct genus of large duck-billed dinosaur that lived in the area currently covered by the state of Montana in the Upper Cretaceous Period (Campanian), approximately 74 million years ago.

Description
Maiasaura was large, attaining an adult length of about 9 meters (30 feet) 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 herding behavior. These herds were extremely large and could have comprised as many as 10,000 individuals.

Discovery
Maiasaura was discovered by dinosaur paleontologist Jack Horner (paleontologic advisor for the Jurassic Park movies) and Robert Makela. He named the dinosaur after finding a series of nests with remains of eggshells and hatchlings at "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.

Reproduction
Maiasaura lived in herds and it raised its young in nesting colonies. The nests in the colonies were packed closely together, like those of modern seabirds, with the gap between the nests being around 7 meters (23 ft); less than the length of the adult animal. 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 to 58 inches (41 to 150 cm) 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.

Contemporaries
Maiasaura lived alongside Orodromeus, Troodon, the ceratopsid Centrosaurus, the tank-like Euoplocephalus and earlier relatives of Tyrannosaurus rex, Daspletosaurus torosus and Albertosaurus. It was among the latest dinosaur species to evolve, prior to the Cretaceous-Tertiary extinction of 65 million years ago.