The class of vertebrates that contains the frogs, toads, newts, and salamanders. The amphibians evolved in the Devonian period (about 370 million years ago) as the first vertebrates to occupy the land. They have moist scaleless skin which is used to supplement the lungs in gas exchange. The eggs are soft and vulnerable to drying, therefore reproduction commonly occurs in water. Amphibian larvae are aquatic, and have gills for respiration; they undergo metamorphosis to the adult form. Most amphibians are found in damp environments and they occur on all continents except Antarctica.