Dinosaur nests found in the Gobi

In July 1923 the Central Asiatic Expeditions of the American Museum of Natural History, led by Roy Chapman Andrews, found fossil eggs in the red sandstone Flaming Cliffs of Bayanzag in Mongolia, in a layer of the Djadochta Formation about 75 million years old. The elongated eggs lay in neat clutches. At the time only a few scraps of dinosaur eggs had been identified, and the discovery provided clear proof that dinosaurs laid eggs.

The expedition thought they belonged to Protoceratops, whose skeletons were abundant at the site. In 1924 a skeleton of a toothless, crested dinosaur found on top of a nest was named Oviraptor, the egg thief, on the assumption that it was raiding the clutch. In the 1990s Mark Norell and colleagues found an oviraptorid embryo inside one of these egg types, and an adult sitting on a nest, showing that the so-called thief was a parent. The discovery opened the study of dinosaur reproduction, nesting and care of young.