Around 340 million years ago, the next major leap in egg evolution came with the first amniotes, not reptiles specifically. These animals evolved the amniotic egg, with protective membranes and, in many lineages, a shell that supported development away from open water. That innovation helped free reproduction from aquatic settings and later passed into both the synapsid line, which led to mammals, and the sauropsid line, which led to reptiles, dinosaurs, pterosaurs, and birds.