What Is the Life Cycle of Reptiles From Eggs to Adults?

Reptiles begin their lives as embryos in amniotic eggs. This means the embryos are cushioned and protected by a surrounding amniotic membrane. These eggs are larger than eggs that do not have amniotic membranes. The egg yolk is another part of the egg; it provides nourishment for the embryo. A separate membrane eliminates waste and provides gas exchange. In most cases, the eggs are buried or placed underground after fertilization. Some reptiles, such as garter snakes, give birth to live young. Some hold the eggs inside until they hatch. A very small group of reptiles compose an exception: The armadillo lizard is one species nourished in a placenta instead of in an egg.

When a reptile is ready to hatch, the creature uses an egg tooth to break through the shell of the egg. Once the shell is opened, the baby will typically remain in the shell for 12 to 48 hours. The little reptile is able to care for and defend himself from birth.

Juvenile reptiles look similar to the adults of their species -- they do not undergo the metamorphosis common in insects and amphibians. Reptiles grow slowly until they reach adult size and sexual maturity. The time a reptile spends as a juvenile varies by species. The green iguana, for example, reaches adulthood and sexual maturity when it is approximately 16 months old and 9 inches long from snout to vent.

Mature reptiles reproduce sexually. Once a male has mated with a female, the female can store the sperm for up to six years to fertilize future hatches of eggs. Once a batch of eggs is fertilized, the female reptile will bury the eggs in a hole or lay them underground. In most cases, the female reptile leaves the eggs to hatch alone. Some reptiles, such as pythons and crocodilians, will care for and protect the eggs until they hatch. Some reptiles who give birth to live young will also provide some care for the hatchlings.

The time a reptile spends in adulthood varies greatly. Some reptiles have fairly short life spans. For example, corn snakes may only live 6 to 8 years in the wild. Other reptiles live much longer. Alligators have life spans of 35 to 50 years; desert tortoises can live 80 years or more.