Maiasaura was named ‘good mother lizard’ because scientists believe it cared for its young after they hatched.
This hadrosaurine is known from a nesting colony found in Montana in the 1970s. It lived in big herds and nested in groups, with possibly as many as 10,000 returning to the same area every year. They probably did so for protection. More than 200 skeletons, embryos, hatchlings, immature and mature adults were found.
Name: Maiasaura, meaning ‘good mother lizard’
Size: about 9m long and 3m high
Food: plants, leaves, fruit and seeds
Lived: between about 90-66 million years ago in the Late Cretaceous in Montana, USA
Maiasaura was a large dinosaur, about as long as a double-decker bus. It usually walked on its long back legs and had a big, flat tail which it held out straight. When feeding on the ground it may have rested on its front legs then reared up on its back legs to reach the leaves of trees. The crest is a short, broad projection above the eyes, and is solid, distinguishing it from the hollow-crested lambeosaurines. The crest, and a pair of triangular projections on the cheekbones, form the basis for the definition of the Maiasaurini. They have batteries of self-sharpening teeth, and a jaw mechanism that allowed the surfaces to grind past each other to chew up tough vegetation.
The nests were hollows, scooped out of muddy ground, and were about the size of a big, round dining room table. The parents may have lined the nest with soft plants, before the female laid between 18 and 30 hard-shelled eggs in it.
Scientists think that Maiasaura mothers, and perhaps fathers as well, guarded the eggs in the nest, protecting them from any dinosaur that tried to steal them. The mothers may have sat on the eggs to keep them warm, going off to feed while other adults watched over them.
When the offspring hatched, the parents looked after them and brought them food. The young dinosaurs ate all sorts of plants as well as fruit and seeds. Maiasaura parents may have chewed up tough plants before giving them to the babies. Experts believe that parents fed the young until they were old enough to leave the nest and find their own food.
Before these offspring were found, scientists thought that female dinosaurs left their offspring to hatch out and take care of themselves alone.
So many nests with skeletons and pieces of eggshell have been found in one place in the USA that some palaeontologists have suggested huge herds of Maiasaura lived in North America. They roamed through the forests, but returned to the same nesting site each year. They probably used the same nests again and again. When the young had grown enough to look after themselves, they stayed with the herd. Eventually, the herd moved on in search of fresh plants to eat.
With no way of defending itself, Maiasaura probably escaped from the big carnivorous dinosaurs by running away and hiding in thick forests. It probably had good eyesight and hearing, which warned it of danger. If Maiasaura was very frightened, it may have plunged into the lakes or rivers. It swam along by waggling its tail and paddling with its front legs.
When palaeontologists discovered a single fossilised nest of Maiasaura in Montana, USA, they decided to excavate the site further. The following year, they returned to their dig and found so many nests, packed closely together, that they named the place ‘Egg Mountain’.