Maiasaura(from the Greek 弮帢巹帢 and the feminine form of Latinsaurus, meaning good mother reptile or good mother lizard ) is a large herbivoroushadrosaurid(duck-billed) dinosaur genus that lived in the area currently covered by the state of Montana in the Upper CretaceousPeriod(mid to late Campanian), about 76.7 million years ago.

Maiasaura walking along a creekbed
Illustration of a herd of Maiasaura walking along a creekbed, as found in the semi-arid Two Medicine Formation fossil bed. This region was characterized by volcanic ash layers and conifer, fern and horsetail vegetation. Author: Debivort

The first fossils ofMaiasaurawere 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 thatthey fed its young while they were in the nest, the first time such evidence was obtained for a dinosaur. Hundreds of bones have been dug up. Evidence suggest the Maiasaura was covered rapidly by a global flood. This preserved the nesting site and fossils.

Maiasaurawas about nine meters long. Young animals walked on their hind legs, adults on all fours.It was probably closely related to Brachylophosaurus.

Maiasaurawere large, attaining a maximum known length of about 9 metres (30ft). They had a flat beak typical ofhadrosaurids, and thick noses. They had a small, spiky crest in front of the eyes. This crest may have been used in headbutting contests between males during the breeding season.

Maiasaura peeblesorum skeletal mount, Brussels Natural History museum (2009).

Maiasaurawere herbivorous. They were capable of walking both on two (bipedal) or four (quadrupedal) legs. Studies of the stress patterns of healed bones show that young juveniles under four years old walked mainly bipedal, switching to a mainly quadrupedal style of walking when they grew larger.They appeared to have no defense against predators, except, perhaps, its heavy muscular tail and their herd behavior. Herds were extremely large and could have comprised as many as 10,000 individuals. Maiasauralived in an inland habitat. Maiasauralived 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 metres (23ft); 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.

Reconstructed nest
Reconstructed nest

It appears that young Maiasaura grew quickly. To some researchers, this suggests that they were warm-blooded. The nests that Horner and Makela found also throw light on the social organization of these hadrosaurs. The number and proximity of the nests indicate that females nested in large groups. Some scientists believe that Maiasaura were strongly social animals that lived in herds of many thousands.Is a characteristic fossil of the middle portion (lithofacies 4) of the Two Medicine Formation, dated to about 76.4 million years ago.Maiasauralived alongside the troodontidTroodonand the hypsilophodontOrodromeus, as well as the dromaeosauridBambiraptorand thetyrannosaurDaspletosaurus.

Also read: Styracosaurus and Tylosaurus

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