What body feature is most responsible for freeing vertebrates from dependence on watery habitats?

The body feature which is most responsible for freeing vertebrates from dependence on water habitat is referred to as Amniote eggs and the shelled.

Amniotes are the membrane which is surrounding the fetus. It comprises of birds, mammals, and reptiles. They their eggs on land and the ones which are fertilized they are retained within the mother.
 Amniotes are being differentiated from anamniotes for example, amphibians and fishes in that anamniotes they lay their eggs in water.