 Amphibian, Amphidians are ectothermic, tetrapod vertebrates of the class Amphibia. Modern Amphidians are all Lysamphibia. They inhabit a wide variety of habitats, with most species living with interest real, vassorial, arboreal or freshwater aquatic ecosystems. Thus Amphidians typically start out as larvae living in water, but some species have developed behavioral adaptations to bypass this. The young generally undergo metamorphosis from larvae with gills to an adult air-breathing form with lungs. Amphidians use their skin as a secondary respiratory surface and some small terrestrial salamanders and frogs lack lungs and rely entirely on their skin. They are superficially similar to lizards but, along with mammals and birds, reptiles are antnotes and do not require water bodies in which to breed. With their complex reproductive needs and permeable skins, Amphidians are often ecological indicators. In recent decades there it has been a dramatic decline in Amphibian populations for many species around the globe. The earliest Amphidians evolved in the Dehonian period from Sarkopterygian fish with lungs and bony limb fins, features that were helpful in adapting to dry land. They diversified and became dominant during the Carboniferous and Permian periods, but were later displaced by reptiles and other vertebrates. Over time, Amphidians shrank in size and decreased in diversity, leaving only the modern subclass Lysimphibia. The three modern orders of Amphidians are annular of frogs and toads. The number of known Amphibian species is approximately 7,000 of which nearly 90% are frogs. The smallest Amphibian and vertebrate in the world is a frog from Nugini-Petophrine and Moritzis with a length of just 7.7 mm 0.30 in. The largest living Amphibian is the 1.8-metre-5 feet-11 in Chinese giant Salamander Andreas David Ion news but this is dwarfed by the extinct 9-metre-30-feet Prionosachus from the Middle Permian of Brazil. The study of Amphidians is called Betrachylogy, while the study of both reptiles and Amphidians is called Herpetology.