Reptiles are known to spend their whole lifetime split between land and water. When they mate, they then have to come out of the water to lay their eggs.
Not only are reptile eggs durable, but they also boast a shell underneath that shields the fluid of the yolk and protects the embryo. The small fluid inside allows the baby creatures to remain safe. This yolk provides the baby food while they grow in the egg.
The young reptiles come out of the egg like a small version of their parents. There are many types of reptiles, including snakes, alligators, lizards, and a Galapagos giant tortoise, of whom these reproduce with eggs. However, other reptiles including some snakes and lizards, are viviparous which means that they do not lay any eggs. Instead, they give birth to a fully developed reptile.
There are many different ways that reptiles can lay their eggs and give birth. If you ever see an unusual egg, think twice before you touch it.
[Source: 100 Things You Should Know About Reptiles]