They may have been cold-blooded, but it turns out dinosaurs were caring parents – arranging their eggs neatly and letting their scaly offspring stay in the nest until they had at least doubled in size.

Fossil-bothering boffins poking around in a 190-million-year-old nest in South Africa have published a new study into the the reproductive and nesting behaviour of early dinos.

Ten nests containing up to 34 small round eggs each, approx 6-7cm (between 2 and 3 inches) in diameter have been discovered in the excavation of an area of sedimentary rock. Small footprints visible around the nests indicate that baby dinos stuck around for a while after hatching - until they had at least doubled in size, says study co-author paleontologist Robert Reisz of the University of Toronto .

And the tight clustering of the eggs indicates that the mother carefully organised them – a sign of maternal affection according to the study authors.

Other clues from the fossils suggest that dinos returned to the same sites to lay their eggs – indicating nesting fidelity, and that they likely assembled in groups to lay their eggs, indicating colonial nesting, a sort of prehistoric pre-natal group – the oldest known evidence of such behaviour in the fossil record.

"This amazing series of 190-million-year-old nests gives us the first detailed look at dinosaur reproduction early in their evolutionary history, and documents the antiquity of nesting strategies that are only known much later in the dinosaur record," says the survey's other lead author David Evans of the Royal Ontario Museum.

The dinosaur studied was the 6m-long (19ft 8in) Massospondylus, an early dinosaur and ancestor of the huge sauropods.

Some of the fossil findings are on display in the Royal Ontario Museum's Dinosaurs Eggs and Babies Exhibition: Remarkable Fossils from South Africa. The study will be published in the Proceedings of the National Academy of Sciences. ®