Amphibian Amphibian For other uses see disambiguation.
 Orders
Subclass Labyrinthodontia extinct
Subclass Lepospondyli extinct
Subclass Lissamphibia
 Anura
 Caudata
 Gymnophiona
Amphibians class Amphibia are a taxon of animals that include all tetrapods four legged vertebrates that do not have amniotic eggs Amphibians from Greek both and life generally spend part of their time on land but they do not have the adaptations to an entirely terrestrial existence found in most other modern tetrapods amniotes There are about living species of amphibians The study of amphibians and reptiles is known as herpetology The fear of amphibians and reptiles is known as herpetophobia.
 History of amphibians.Amphibians developed with the characteristics of pharyngeal slits gills a dorsal nerve cord a notochord and a post anal tail at different stages of their life They have persisted since the dawn of tetrapods million years ago in the Devonian period when they were the first four legged animals to develop lungs During the following Carboniferous period they also developed the ability to walk on land to avoid aquatic competition and predation while allowing them to travel from water source to water source As a group they maintained the status of the dominant animal for nearly million years Throughout their history they have ranged in size from the foot long Devonian Ichthyostega to the slightly larger foot long Permian Eryops and down to the tiny Brachycephalus didactylus Brazilian Gold Frog and Eleutherodactylus iberia from Cuba with a total length of millimeters Amphibians have mastered almost every climate on earth from the hottest deserts to the frozen arctic and have adapted to climatic change with ease.
 Solomon Berg Martin Biology
 Duellman Trueb Biology of Amphibians
 Classification.Traditionally the amphibians are taken to include all tetrapods that are not amniotes Recent amphibians all belong to a single subgroup of these called the Lissamphibia Recently there has been a tendency to restrict the class Amphibia to the Lissamphibia i e to exclude tetrapods that are not more closely related to modern forms than they are to modern reptiles birds and mammals.
There are two ancient extinct subclasses.
 Subclass Labyrinthodontia paraphyletic. Subclass Lepospondyli
Of the remaining modern subclass Lissamphibia there are three orders.
 Order Anura frogs and toads in Superorder Salientia species
 Order Caudata or Urodela salamanders species
 Order Gymnophiona or Apoda caecilians species
Authorities disagree on whether Salientia is a Superorder that includes the order Anura or whether Anura is a sub order of the order Salientia In effect Salientia includes all the Anura plus a single Triassic proto frog species Triadobatrachus massinoti Practical considerations seem to favour using the former arrangement now.
 Reproduction.For the purpose of reproduction most amphibians are bound to fresh water A few tolerate brackish water but there are no true sea water amphibians Several hundred frog species in adaptive radiations e g Eleutherodactylus the Pacific Platymantines the Australo Papuan microhylids and many other tropical frogs however do not need any water whatsoever They reproduce via direct development an ecological and evolutionary adaptation that has allowed them to be completely independent from free standing water Almost all of these frogs live in wet tropical rainforests and their eggs hatch directly into miniature versions of the adult bypassing the tadpole stage entirely Several species have also adapted to arid and semi arid environments but most of them still need water to lay their eggs The larvae tadpoles or polliwogs breathe with exterior gills After hatching they start to transform gradually into the adult's appearance This process is called metamorphosis Typically the animals then leave the water and become terrestrial adults but
there are many interesting exceptions to this general way of reproduction.