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Maiasaura

Maiasaura is a duckbill dinosaur - or hadrosaur - rather typical: it has a small head, a rather chunky torso, an extremely rigid tail and its hind legs are longer than its front legs. Maiasaura is however more interesting than the majority of other hadrosaurs since herd behavior is known by indisputable evidence and moreover this dinosaur has become famous because of its irreproachable parenting habits as evidenced by the nests found at Egg Mountain in Montana.

Maiasaura, which means "good mother lizard", ends with the suffix "a" rather than the usual "us". And as fate would have it, it was a female fossil hunter, Laurie Trexler, who unearthed the Maiasaura holotype specimen on an expedition to Two-Medicine in 1978.

Egg Mountain

In 1978, the renowned paleontologist Jack Horner and a team of researchers discovered in an outcrop of the Two-Medecine formation, just south of the town of Choteau, 14 well preserved dinosaur nests. This earned the site the name of Egg Mountain and it is the first real evidence that some dinosaurs cared for their toddlers. Thanks to skeletal fossils discovered sometime earlier in the region, it was possible to associate these nests with the hadrosaur dinosaur Maiasaura peeblesorum, frequently referred to as the caring mother. Since Jack Horner's initial discovery, hundreds of specimens have been dug at Two-Medicine, including eggs, juveniles and adults. The Egg Mountain site is well renowned in the world of paleontology.

Maiasaura, the caring mother

Findings at Egg Mountain suggest that this dinosaur exhibited colonial nesting behavior where large herds congregated at a single location to establish breeding grounds. After hatching, adults took care of the young for a long time, until they were able to follow the group on their own.

Rather than incubating the eggs by sitting on them as birds do, Maiasaura meticulously prepared the nest by strewing different kinds of vegetation which generated heat when it rotted in the humidity of the jungle. This vegetation could also be used to feed the young after hatching.

Maiasaura could lay up to 30 or 40 eggs simultaneously which greatly increased birth and survival rate against predators of the time such as the highly intelligent Troodon, the threatening Daspletosaurus or the fast Bambiraptor.

By studying the bones of this dinosaur, we realized that it had an exceptionally fast growth rate. Thus, in the first year of their existence, young Maiasaura’s grew to over 3 feet in size and reached their adult size of 30 feet for a weight of 5,000 lbs in a period of only 8 to 10 years.

Seasonal migration

Given that this dinosaur reached a colossal size and that it congregated in huge herds of several thousand individuals, some paleontologists have come up with the hypothesis that Maiasaura had to make regular seasonal migrations to meet the huge food demand that required such groups.

It was also suggested that like sea turtles, this dinosaur would return to lay its eggs at the very spot where it was born.

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