Illustration of a large oviraptorosaur incubating a ring of eggs

A type of feathered dinosaur called an oviraptorosaur broods its eggs in this artist’s rendering. Credit: Masato Hattori

Palaeontology

Why dinosaurs arranged their eggs in a doughnut shape

A 1,600-kilogram brooding parent could be a danger to developing offspring.

Massive dinosaurs built specially designed nests to avoid crushing their eggs during incubation.

All modern birds with open-topped nests sit on them to keep the developing eggs warm. To find out whether egg-laying dinosaurs were able to do the same, Kohei Tanaka of Nagoya University Museum in Japan and his colleagues studied 40 clutches of fossilized eggs laid by oviraptorosaurs, a group of feathered dinosaurs that walked on two legs.

After analysing the eggshells’ structure, the authors concluded that oviraptorosaurs, which ranged in size from 40 to 1,600 kilograms, built open nests. The largest species laid eggs with relatively thin, weak shells. But the animals apparently compensated for this fragility and the threat of their own immense weight by laying a ring of eggs around a large central opening. This might have allowed the centre of the nest to bear some or all of the brooding parent’s weight, the authors say.