Amphibian larvea are often aquatic and go through a complex metamorphosis process as they grow to adulthood. They have moist skin and do not have scales, feathers or hair. The life cycles of amphibians reflects their evolutionary history of bridging land and water. Most amphibians lay their eggs in freshwater. A few species tolerate brackish water and some species lay their eggs on land. Extraordinarily, some species even carry their eggs inside their body. Although life cycles of amphibians vary from species to species, they all share the following three basic stages of development: egg, larva, adult.
There were no birds, no mammals, and no reptiles on land (or in the water for that matter). There were only invertebrates and an assortment of prehistoric plants. It was a silent place, void of birdsong and lacking the growl of predators. The land lay wide open to amphibians and those with the evolutionary tenacity to set forth from the shallow shores began a new and important stage in the history of life on our planet. Several types of fishes had developed lungs. Among those lung-bearing fishes were the lobe-finned fish and the lungfishes.
The Crossopterygians, a group of primative lobe-finned fish are believed to be the ancestors of amphibians. They evolved several key features that enabled them to colonize land—a more rigid skeleton that would support the animal's body weight on land, nostrils, and leg bones.
Most lineages of amphibians never fully severed their ties with aquatic habitats. A majority of amphibian species return to the water to breed and some species remain entirely aquatic throughout their entire life cycle. Most amphibians go through a complex metamorphosis process as they grow to adulthood.