Amphibia

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Amphibia(amphibians) A chordate class represented today by just three groups, of which the salamanders (Urodela) and frogs and toads (Anura) are the best known. They are poikilothermic vertebrates. The majority are terrestrial but develop by a larval phase (tadpoles) in water. The skin is soft, naked (non-scaly), rich in mucous and poison glands, and important in cutaneous respiration. There are about 3000 extant species. Most are found in damp environments and they occur on all continents except Antarctica. The class was formerly much more varied and in the Triassic some forms (e.g. Mastodontosaurus) grew up to 6 m long. Amphibians appeared first in the Devonian, having evolved from the Rhipidistia (lobe-finned fish), flourished in the Carboniferous and Permian, but declined thereafter. The first modern types were established during the Triassic.

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