Tiny footprints and fossil embryos at the oldest dinosaur nesting site ever found have revealed new details about how these ancient creatures reared their young.

The nest belong to mid-sized dinosaurs from the early Jurassic period known as Massospondylus, which grew to four to six metres long as adults. Their eggs, however, are only six centimetres in diameter.

The traces left behind show that hatchlings stayed in the nest until they doubled in size, and that the young Massospondylus walked on four legs while young, but then likely stood upright on two legs as adults.

The analysis led by Canadian and South African researchers is based on findings at an excavation in Golden Gate Highlands National Park in South Africa, and is published in the Proceedings of the National Academy of Sciences.

The fossils date to 190 million years ago, presenting the oldest known evidence of such behaviour among dinosaurs.

Researchers believe the layout of the nests suggest that the site was returned to repeatedly by the dinosaur mothers, who laid eggs together as a group and carefully organised their eggs in their nests.