Maiasaura: The Cretaceous plant-eater that raised its young

Maiasaura has "good mother" written into its story, because it left behind an extraordinary fossil site — nests, eggs, babies and adults together. It lived during the Late Cretaceous in what is now Montana, United States, and was a duck-billed dinosaur.

Its body

Maiasaura belonged to the hadrosaurs, a group of large plant-eating dinosaurs roughly 7 to 9 metres long. It could walk on its two hind legs and also drop onto all fours — a flexible way to move. The front of its broad "duck-billed" mouth held rows of teeth that ground up plant material. Large eyes and nostrils helped it sense its surroundings keenly.

Where it lived and what it ate

Maiasaura fed on plants, cropping ferns, conifers and shrubs with its beak. It was a social animal, probably moving in groups on a regular route. Fossils suggest it may have built nests near water, laying its eggs in mounds of soil or vegetation.

Where its fossils were found

Maiasaura fossils come mainly from the Two Medicine Formation in Montana, United States. That layer preserves a famous "Egg Mountain" site, where a whole area of nests and eggs was discovered, making Maiasaura a key animal for studying how dinosaurs reproduced, grew and behaved in groups.

What the fossils tell us — and what they do not

Nests, eggs, babies and adults preserved together help us reconstruct its breeding and growth. But the idea that "adults fed the young for a long time" is still a careful scientific inference — whether parents cared for the young, and for how long, is still being studied. A cautious view is that the evidence supports some degree of parental care, but it should not be stated too strongly.

A note for grown-ups

You could talk with a child about how we decide there was parental care: a nest and eggs are not enough — we also need to see whether the babies actually stayed in the nest with adults nearby. That is a good example of "having enough evidence before drawing a conclusion".