Amphibians are a Class of vertebrate animals that can live in water and on land. Common examples are frogs and salamanders. The young generally undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a secondary respiratory surface and some small terrestrial salamanders and frogs lack lungs and rely entirely on their skin.
With their complex reproductive needs and permeable skins, amphibians are often ecological indicators; in recent decades there has been a dramatic decline in amphibian populations for many species around the globe.
Amphibians evolved from fish with lungs and bony-limbed fins. They diversified and became dominant during the Carboniferous and Permian periods (see video When Giant Amphibians Reigned: https://youtu.be/rGthtRZl8B0), but were later displaced by reptiles and other vertebrates. Most amphibians are now small and many are threatened by extinction.