Maiasaur lived about 80 million years ago. It was one of the last kinds of dinosaur living just before they died out 65 million years ago. Maiasaur grew to be 30 feet long, which is about the size of a school bus. It was about eight feet tall at the hips. Maiasaur weighed about four tons. It was part of the family of dinosaurs that had a snout like a duck’s beak. These dinosaurs were called hadrosaurs. Maiasaur had a flat skull with small crests above its eyes. It had four fingers on its hands and its back feet had hard toes like a deer. Maiasaur normally walked on four legs, but when it needed to run quickly, it would run on its hind legs. It was a fast runner. Its long, thick tail was good for balance. Running was its only way to escape hunting carnivores like Deinonychus and Troödon.
Maiasaur was a large herbivore, meaning that it only ate plants. An adult Maiasaur would need to eat about 200 pounds of leaves, berries and seeds every day to stay alive. It would snip down plants with its toothless beak and chew them up with its grinding back teeth. Maiasaur had cheek pouches, so it could store food in its mouth and chew everything carefully before swallowing. These dinosaurs moved about in huge groups. When the food in one place was eaten, the Maiasaur would all move together to another place. They moved with the young on the inside of the group and the adults on the outside. They did this to protect their babies from predators.
About 10,000 Maiasaur fossils were found together in one place. Paleontologists call this bonebed “Egg Mountain”. The adult Maiasaur were found by their nests, near their eggs and babies. The nests were about 25 to 30 feet apart, about the length of an adult Maiasaur. There were holes dug in the ground, about 6 feet across. Each nest held about 25 eggs. Each egg was about the size of a grapefruit. Newly hatched Maiasaur babies were about 1 foot long. The babies could walk as soon as they were hatched. But baby Maiasaur stayed in the nest and were fed by their mothers until they were older. This is how Maiasaur got its name, which means “good mother lizard”. The Egg Mountain group of Maiasaur probably all died at the same time, buried during a big volcano eruption.