Montana: Maiasaura peeblesorum (state fossil)

One of the most important dinosaurs discovered in the late 20th century, the Montana state fossil, Maiasaura peeblesorum, gave science new insights into the social behavior of dinosaurs. A type of hadrosaur or duckbilled dinosaur, Maiasaura inhabited the coastal lowlands of Montana bordering the Western Interior Seaway during the Late Cretaceous Period, about 75 million years ago. Scores of skeletons of this dinosaur have been found together, including eggs, nests, and babies, indicating that Maiasaura was a herding animal that used communal nesting grounds and probably maintained nurseries or crèches like some modern birds do. Its name means "good mother lizard."

The hadrosaur grouping includes many large plant-eating dinosaurs, some with elaborate crests on their skulls. Maiasaura itself had only a tiny crest, but grew to around 30 feet long and weighed 3 - 4 tons. It probably walked quadrupedally most of the time, but could stand on just its back legs when feeding on high vegetation.

The first fossils of Maiasaura were found on a ranch near Choteau in 1977. Shortly thereafter, they came to the attention of paleontologists, who scoured the Two Medicine Formation and found more adult and baby dinosaurs, and a nesting site nicknamed "Egg Mountain." The site is now owned by the Nature Conservancy, which leads annual digs there.

Because of its scientific importance, a group of middle school students and rockhounds led a drive to crown Maiasaura the state fossil. The legislature passed Bill 130 with a unanimous "yea," and it was signed into law by the governor on February 22, 1985.

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Montana symbols

Maiasaura