Eggs, Nest and Embryos

Article | Updated 10 years ago

Extinct non-avian dinosaurs laid eggs like modern birds (avian dinosaurs) do.

Large dinosaurs like sauropods (long-necked dinosaurs), hadrosaurs (duck-billed dinosaurs) and therizinosaurs laid spherical eggs, whereas smaller theropods laid elongated ones.

Sauropod nests

Female sauropods dug an elongated pit and laid up to 28 eggs in it, most likely in one sitting. Most sauropod species had eggs with quite porous shells, so oxygen and carbon dioxide could pass through the shell. Their eggs were probably covered with sand or plant material to stop water loss through the shell.

Hatchling predator
Several sauropod nests have been discovered in India with the skeletons of the ancient snake Sanajeh. Fossils such is this, of a Sanejeh curled around crushed eggs, indicate it preyed on baby dinosaurs.


Oviraptor nests

A fossilised pelvis of a female oviraptor dinosaur found with eggs inside, shows that they produced two large, elongated eggs at a time. Their nests are bowl-shaped and contain up to 24 eggs arranged in a ring. These were probably laid over 2–4 weeks. The eggs were not very porous so they were unlikely to be buried. Instead the female, or perhaps the male, would sit on the nest.