Maiasaura
Updated: January 20, 2026
Maiasaura: Montana's "Good Mother" Dinosaur
Maiasaura was a duck-billed dinosaur from the hadrosaur family. These dinosaurs lived during the Late Cretaceous Period and were plant-eaters. They walked mostly on two legs, had long flat snouts, and a small bump between their eyes. Adults were about 30 feet long and weighed 3 tons, while babies were only 14 inches long when they hatched.
One of the most important dinosaur discoveries in the world happened in Montana at a site called Egg Mountain. Scientists found nests, eggs, embryos, and baby dinosaurs there-the first proof that some dinosaurs cared for their young! Maiasaura built large bowl-shaped nests about 6 feet wide, holding up to 20 eggs. Babies stayed in the nest for about two months, and scientists believe parents brought food to them, just like birds do today.
Maiasaura grew very fast-up to 10 feet in one year-which suggests they may have been warm-blooded. Their bones look more like those of warm-blooded animals than reptiles. They also had special teeth called a dental battery, with about 150 teeth for grinding tough plants and even wood fibers.
In 1985, Montana schoolchildren helped make Maiasaura the official state fossil. They wrote letters, collected thousands of signatures, and even baked dinosaur cookies for lawmakers! Thanks to their efforts, Maiasaura became a symbol of Montana’s amazing dinosaur history.
Key Facts about Maiasaura and Egg Mountain
- Maiasaura was a duck-billed hadrosaur from the Upper Cretaceous, about 30 ft long and 3 tons; hatchlings were 14 inches and grew fast.
- Hadrosaurs were bipedal plant-eaters with flat snouts, crests, and specialized teeth for grinding tough plants.
- Egg Mountain in Montana revealed nests, eggs, embryos, and juveniles-first proof dinosaurs cared for their young.
- Nests were 6 ft wide, held up to 20 eggs, and babies stayed for two months, likely fed by parents.
- Evidence suggests Maiasaura may have been warm-blooded due to rapid growth and bone structure.
- Teeth formed a dental battery with about 150 teeth, continuously replaced for chewing plants and wood fibers.
- Maiasaura became Montana's state fossil in 1985, thanks to a campaign led by schoolchildren.
Download a study sheet about the Maiasuar!
For more information about dinosaurs in Montana follow the Montana Dinosaur Trail.
Updated: January 20, 2026