Like the eggs of later pterosaurs and modern reptiles, the eggs of "Darwinopterus" had a parchment-like, soft shell. In modern birds, the eggshell is hardened with calcium carbonate, completely shielding the embryo from the outside environment. Soft-shelled eggs are permeable to water, and allow significant amounts to be absorbed into the egg during development. Eggs of this type are more vulnerable to the elements and are typically buried in soil. 