Reptile reproduction varies between species. Most reptiles reproduce sexually, while a few are capable of asexual reproduction. There are six families of lizard and one family of snake that are known to reproduce asexually through parthenogenesis. Depending on the species, reptiles reproduce by either laying eggs or giving birth to live young. Whatever form of reproduction reptiles utilize to produce offspring, it all begins with courtship.
Many reptiles have elaborate courtship rituals, some are colorful while others are like a dance. Male chameleons undergo color change during courtship, while females display vibrant colors when they are pregnant and are not receptive to mating. Snakes emit a chemical scent known as pheromones to attract a partner. A male snake, once he has located a receptive female, will court her by repeatedly crawling over her then bringing his tail in line with hers so that mating may occur. Male turtles typically will court a female by bobbing his head, while some will use the claws of their forelimbs to stroke a female's face.
Male and female reptiles do not have external genitalia, however they do possess different reproductive organs. Males possess two testicles and a copulatory organ housed inside the body. The male copulatory organ is either a single penis or a hemipenis (two penises), it is not connected to the urinary tract and is strictly an organ of reproduction. Males that have a hemipenis only use one at a time, and some males alternate between copulations. Male tuataras differ from other reptiles as they do not possess a penis, instead they deliver sperm to the female by utilizing the muscular opening of the cloaca. Fertilization occurs internally, female eggs are fertilized by the male's sperm inside the female's body.
Excluding some lizards and snakes which give birth to live young, all other reptiles lay eggs. Reptile eggs are self-sufficient, they contain a yolk and protein which provides the embryo with the water and nutrients needed to develop. The eggs, although encased in a hard or leathery shell, allows for the exchange of oxygen and carbon dioxide. The shell also protects the embryo from drying out or being attacked by bacteria. Some species produce more eggs or young than others. The number can vary greatly between species and even vary within the same species. Some turtles will lay one or two eggs, while other turtles may lay up to 150 eggs several times. The American garter snake is an example of the variance within the same species, they can give birth to litters ranging from 3 to 100 young. Typically, reptiles will deposit their eggs in a nest and leave them unattended to hatch on their own. Their are a couple of exceptions, pythons will coil around their eggs to generate heat and speed up the development process as well as protect the eggs from predators. Crocodiles will guard their nests and may even assist a young crocodile that is having difficulty getting out of its egg.
Reptiles are fully developed upon hatching or birth, and are ready for an independent existence. Baby reptiles are the favorite prey among other animal and face many odds in the early months of their lives, if they survive to maturity, many live an very long life span.