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The Lissamphibia are a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: the Salientia (frogs, toads, and their extinct relatives), the Caudata (salamanders, newts, and their extinct relatives), and the Gymnophiona (the limbless caecilians and their extinct relatives). A fourth group, the Allocaudata, was moderately successful, spanning 160 million years from the Middle Jurassic to the Early Pliocene, but became extinct 3.6 million years ago. For several decades, this name has been used for a group that includes all living amphibians, but excludes all the main groups of Paleozoic tetrapods, such as Temnospondyli, Lepospondyli, Embolomeri, and Seymouriamorpha. Some scientists have concluded that all of the primary groups of modern amphibians, the frogs, salamanders, caecilians are closely related, but others〔 hold that frogs and salamanders evolved from temnospondyls, while caecilians evolved from lepospondyls, so Lissamphibia is polyphyletic with respect to other tetrapods. Some writers have argued that the early Permian dissorophoid ''Gerobatrachus hottoni'' is a lissamphibian.〔 If it is not, the earliest known lissamphibians are ''Triadobatrachus'' and ''Czatkobatrachus'' from the Early Triassic. ==Characteristics== Some, if not all, lissamphibians share the following characteristics. Some of these apply to the soft body parts, hence do not appear in fossils. However, the skeletal characteristics also appear in several types of Palaeozoic amphibians: * Double or paired occipital condyles * Two types of skin glands (mucous and granular) * Fat bodies associated with gonads * Double-channeled sensory papillae in the inner ear * Green rods (a special type of visual cell, unknown in caecilians) * Ribs do not encircle body * Ability to elevate the eyes (with the levator bulbi muscle) * Forced-pump respiratory mechanism * Cylindrical centra (the main body of the vertebrae; cylindrical centra are also found in several groups of early tetrapods) * Pedicellate teeth (the crowns of the teeth are separated from the roots by a zone of fibrous tissue; also found in some Dissorophoidea; the teeth of some fossil salamanders are not pedicellate) * Bicuspid teeth (two cusps per tooth, also found in juvenile dissorophoids) * Operculum (small bone in the skull, linked to shoulder girdle by the opercularis muscle; perhaps involved in hearing and balance; absent in caecilians and some salamanders, fused to the columella (ear bone) in most anurans) * Loss of posterior skull bones (also in Microsauria and Dissorophoidea) * Small, widely separated pterygoid bones (also found in Temnospondyli and Nectridea) * Wide cultriform process of the parasphenoid (also found in some Microsauria (''Rhynchonchos'') and Lysorophia) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lissamphibia」の詳細全文を読む スポンサード リンク
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