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How do amniotic membranes help reptile embryos develop on land?

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A painted turtle (Chrysemys picta) with a dark shell and red and yellow markings rests on a rock near water, surrounded by green aquatic plants. — reptile Painted turtle (*Chrysemys picta*).

Amniotic membranes are a critical evolutionary adaptation that allowed reptiles to transition to fully terrestrial environments by enabling their embryos to develop within a self-contained, protective system. These membranes—the amnion, chorion, and allantois—function together to support the embryo outside of water.123

The specific roles of these membranes include:

Amnion: This membrane forms a fluid-filled cavity that suspends the embryo, providing a cushion against mechanical injury and shock. It also protects the embryo from drying out and prevents tissue adhesions.43
Chorion: This layer surrounds the entire embryo and, along with the amnion, helps create the protective, fluid-filled chamber.3
Allantois: This sac serves as a collection area for nitrogenous waste products and facilitates gas exchange, allowing the embryo to breathe through the eggshell.13

Together with a protective shell, these membranes create a "closed system" that prevents desiccation, allowing reptile embryos to thrive on land without needing to return to water to reproduce.13