Gestation is the period of time between fertilization and birth. The animal with the longest gestation period is not a mammal; it is the viviparous (give birth to live young) amphibian, the alpine black salamander, which can have a gestation period of up to thirty-eight months. It lives at altitudes above 4,600 feet (1,402 meters) in the Swiss Alps and most often has two fully metamorphosed young.