The fossil record is rich with dinosaur eggs – thousands of specimens have been discovered. Many are fragmentary, but some are exquisitely preserved, with embryos resembling those of modern birds inside.
Most dinosaurs produced eggs that were leathery and flexible, similar to those of some modern snakes, lizards and turtles. However, it’s not impossible that some dinosaurs laid even softer eggs, like those of tuataras and many snakes and lizards.
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But those shells desiccate and shrivel up once the animal has hatched, so fossilisation would be unlikely.
The fossil record indicates that early members of all dinosaur lineages laid eggs with pliable shells. Chemical analysis has revealed that the amount of calcium in fossilised shells was similar to that found in a freshly-laid, squishy reptile egg today.
This conclusion has been further validated by the fracture patterns of fossilised eggs: the manner in which the shells broke indicated that they were leathery in texture rather than brittle and solid.
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But we know that some later dinosaurs did lay eggs with hard shells, just like their nearest relatives – modern crocodilians and birds. The increased amounts of calcium in these shells meant they were more conducive to fossilisation.
These findings have implications for how dinosaur eggs were incubated and hatched. Softer-shelled eggs may have been buried, like those of modern turtles, while dinosaurs may have used their bodies to keep harder-shelled eggs warm.
These stronger shells would have been more capable of sustaining their weight. Such was the case with Oviraptor – remarkable fossils have preserved parents on top of their nests.
