Why was the advent of the amniotic egg so important in the evolution of terrestrial vertebrates?

The evolution of egg was the most important evolutionary incident which allowed the evolution of the terrestrial animals. The amnion is the layer inside the chorion of the egg which keeps the embryo from drying out.

The formation of this layer completely removed the dependency of the organism to lay their eggs in the water to keep them wet.

This layer allowed the reptiles to lay their eggs on the land as the amnion can protect the embryo from drying out. The other layer of eggs protects the egg from the predators and the pathogens.

Thus, the evolution of the amniotic egg is very important from the evolutionary perspective.