What do we know about dinosaur breeding habits?

As far as we know, all dinosaurs lay eggs rather than giving birth to live young. Many of these eggs have been fossilized, but it is sometime difficult to find out which animal produced them. Sometimes the eggs contain the remains of an unhatched baby dinosaur. Occasionally, the fossil of a newly hatched baby is found near the eggs, showing which species they belong to. Dinosaur eggs were laid in clutches, like those of today’s birds. We think that dinosaurs, like birds, would have had courtship behavior, built nests and cared for their young until they were old enough to look after themselves.

Originally, it was thought that dinosaurs laid their eggs in isolated places, but in 1978 a remarkable find was made in Montana, USA. Fifteen Maiasaurus babies were found scattered around a large mound-shaped structure, together with many broken eggshells. The babies were not newly hatched because their teeth were partly worn. The nest was about 2m across, and covered with vegetation. in the Gobi desert, the pig-sized dinosaur Protoceratops dug holes in the sand and buried her eggs. She left them to hatch in the heat of the sand while she guarded them from predators.

Dinosaur eggs looked very much like bird's eggs and were surprisingly small. Most were about the size and shape of a large potato. Their small size means that the hatchling would also have been small, and would have needed plenty of care from its parent.

There is good evidence to show that dinosaurs such as the Maiasaurus migrated back to its traditional nest site every year, where it laid up to 20 eggs. Scientists have found nest sites containing masses of eggshells, together with the remains of babies of various ages, showing that the dinosaurs re-used the sites over the years.