Definition: Amphibians are remarkable animals that include modern-day frogs, toads, caecilians, newts, and salamanders. These animals are the descendents of the first vertebrates to make the move from life in water to life on land. Despite their early colonization of terrestrial habitats, most lineages of amphibians have 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.