Reptiles can be divided into three major groups: crocodiles, lepidosaurs (snakes and lizards), and turtles. Of the three, live birth is only seen in lepidosaurs. Even among lepidosaurs, most lay eggs that hatch into young, but there are a few lizards and snakes that give birth to live young. Reptiles that give birth to live young can be divided into two types: viviparous and ovoviviparous. The following are reptiles that give live birth:

• Viviparous Reptiles: Viviparous vertebrates are animals that retain their fertilized eggs in their reproductive system until the developing offspring are ready to be born. In viviparous reptiles, eggs mature in the animals oviduct until they emerge as smaller versions of the adult. Viviparity is more common in snakes than in other reptiles -- occurring in 14 families of snakes and 20 percent of species. Nine nominal families have both egg-laying and viviparous snakes. From sea snakes to garter snakes, viviparous snakes live in a variety of ecosystems and come in a range of sizes. Other live-bearing snakes include boas, pit vipers, and spitting cobras.

• Ovoviviparous Reptiles: Ovoviviparous animals are a sub-type of viviparous animals that also develop their fertilized eggs inside the reproductive tract. The difference is that the young hatch from their eggs inside the mother, then emerge into the world after this internal hatching. In addition to a few reptile species, several species of amphibians and fish, such as the sand shark, are born this way.

In summary, snakes and lizards are the only reptiles that give live birth, and they can be either viviparous or ovoviviparous. Viviparity is more common in snakes than in other reptiles, and there are a few lizards that give birth to live young as well.