Maiasaura peeblesorum

Maia in Ancient Greek meant mother, wet nurse. It is thought that this hadrosaur would look after its youngsters. In any event, it used to nest in huge colonies that were frequented generation after generation. But the Maiasaura may not have been such a good mother as all that: no bones of the babies and adults have ever been discovered together! Perhaps the very young hadrosaurs stayed apart for 1 or 2 years before joining the rest of the group, when they would be big enough to follow the adults during their travels.
Just like tree trunks, dinosaur bones have growth rings so an estimate can be made of the age of the specimens and how fast they grew. For example, the Maiasaura grew from 30 cm at birth to nearly 4 m in only 1 or 2 years, to reach adult size, roughly 9 m, between 6 and 8 years old. It was safer growing quickly because predators were more likely to attack a defenceless young creature than a healthy adult.