The image of dinosaurs as instinct-driven, cold-hearted predators has been overturned by a remarkable body of fossil evidence. Some dinosaurs — particularly those most closely related to modern birds — showed parental behaviour that would not look out of place in a nature documentary today.
Maiasaura: The 'Good Mother Lizard'
The most dramatic evidence for dinosaur parental care came from the Two Medicine Formation of Montana in the 1970s, when palaeontologist Jack Horner and his colleagues discovered something extraordinary: a nest site containing multiple Maiasaura nests, with hatchlings at various stages of development, all associated with adult remains.
The juveniles' leg bones showed wear consistent with movement — they weren't fresh hatchlings. Their teeth showed wear from chewing. But they were too small to have foraged independently. The only plausible explanation: parents were returning to the nest to feed their young, over an extended period after hatching. This was the first solid evidence that any dinosaur had engaged in active post-hatching parental care, and it earned Maiasaura its name: Greek for 'Good Mother Lizard'.
Egg Mountain in Montana, where Maiasaura nests were discovered, contains tens of thousands of eggs and bones — evidence that this species nested colonially in enormous aggregations, perhaps similar to modern flamingo colonies.
Brooding Oviraptors
When Oviraptor was first described in 1924, a specimen found on top of a nest of eggs was assumed to be stealing them — hence the name 'egg thief'. This interpretation stood for seventy years. Then, in 1993, a near-identical specimen was found in the same position — but this time, the embryos inside the eggs were identifiable as Oviraptor embryos. The animal wasn't stealing eggs. It was brooding its own.
Several brooding Oviraptor specimens have now been found, all in a posture identical to that of modern brooding birds: body lowered over the egg clutch, arms spread to cover the outer eggs, head oriented forward. The fossil evidence for active egg incubation in oviraptorosaurs is now overwhelming.
Sauropod Herding and Nest Sites
Sauropod parental behaviour is harder to document, given the difficulty of preserving behaviour in large, terrestrial animals. However, titanosaur nesting sites in Auca Mahuevo, Patagonia — where hundreds of thousands of eggs are preserved — suggest colonial nesting in specific, repeatedly used sites, similar to modern sea turtles. The sheer density of eggs at some sites implies that females may have returned to the same locations across generations.
Evidence from sauropod trackway sites suggests that juveniles sometimes moved in groups with adults — consistent with some form of protective herd behaviour, though not necessarily active parental care in the primate sense.
The Broader Pattern
The general pattern that emerges from the fossil record is that parental care was most developed in the coelurosaur theropods — the group most closely related to modern birds — and became progressively more elaborate as the lineage approached Aves. This is exactly what evolutionary theory predicts: the cognitive and behavioural complexity required for parental care co-evolved with the larger brains and more sophisticated social behaviour that characterise this part of the dinosaur family tree. Far from being cold and indifferent, at least some dinosaurs were among the most devoted parents of their era.