Amphibians

Amphibians are cold-blooded tetrapod vertebrates. Amphibians are basal tetrapods and initially they were very diversified, but currently only one large amphibian group survives, with mainly small-sized species. They however conquered many habitats, having terrestrial, fossorial and aquatic habitats. Most amphibians start their life as aquatic larvae. The gilled, water-breathing larva usually grow to a air-breathing lunged adult. Amphibians have a secondary form of respiration, using the skin as a bonus-breathing feature to the lungs, although some species can rely more on this secondary form of breathing than usual. Tailed terrestrial amphibians can often resemble lizards, but lizards are amniotes, and do not require water to lay their eggs and breed. Amphibians are good indicators of eccological health, as they have many complex requirements for survival. The first amphibians evolved in the Late Devonian as nearly fish-like semi-aquatic lunged animals, with finned limbs that crudely helped them walk on land. They were initially abundant and diversified in the Carboniferous and Permian, only to get replaced, mostly, by reptiles and other more advanced vertebrates. Today, amphibians only represent a small-sized and less diverse lineage of amphibians that managed to avoid competition from amniotes. There are three surviving orders of amphibians, being the two most notorious the Anura (frogs) and Urodela (salamanders). There are 7000 species of extant amphibians, nearly 90% of them are frogs. Historically, amphibians ranged in size from the size of half a US dime's diameter, to the length of an orca.