The Maiasaura nests in Montana
USA, have been the subject of the most studies on dinosaur family life. (dinosaur equipment)The Montana nesting site was by a lake in the uplands. Besides nesting behaviour, this site also provided all sorts of information about how the animals lived and grew. Once out of the egg, a baby Maiasaura was a small, vulnerable animal, about 45cm (18in) long. It remained in the nest and was nurtured by its parents, who brought food in the form of leaves and fruits to the nest. Nests were protected against raids by large lizards and theropod dinosaurs, such as Troodon. Seasonal climates meant that once in a while the Maiasaura herd had to leave the upland nesting site and migrate to the coastal plains, where food was still plentiful. The nestling grew to twice its birth length in about five months. (Dinosaur costume)At this juvenile stage the young dinosaur would have left the nest, and followed the parents, learning how to find food for itself. Juveniles continued to grow, and after about a year reached a length of about 3.5m (11 ft).
The microscopic structure of the bones show us that the full adult length of about 7m (23ft) was reached in about six years, after which time the growth rate became very much slower. (dinosaur playground equipment)The conclusion is that dinosaurs, or at least duckbill dinosaurs, grew extremely quickly in the early part of their lives, and that the growth rate then slowed. This is the same growth pattern that we see in modern mammals and birds, but not in reptiles. The Maiasaura herds returned to their nesting area when it was time to breed, a round trip of around 300km (185 miles).