Any member of a class (Amphibia) of cold-blooded vertebrate animals that includes more than 4,400 species in three groups: toads (order Anura), salamanders (order Caudata), and caecilians (order Apoda).
Probably evolved from certain fish species of the Early Devonian period (417–391 million years ago), amphibians were the first vertebrates to move from an aquatic environment to land. Most species have an aquatic larval, or {{link=tadpole">tadpole , stage that metamorphoses into a terrestrial adult, but a few species spend their entire life in water. Amphibians are found worldwide, the majority in the tropics.