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''Lethiscus'' is the earliest known representative of the Aïstopoda, a group of very specialised snake-like amphibians known from the Carboniferous and Permian. ''Lethiscus'' is known from only a single specimen from the Holkerian Stage (Middle Viséan) of the Early Carboniferous (Middle Mississippian) of Scotland, and is one of the oldest known post Devonian tetrapods. Despite its very early date, it was already a highly advanced animal. The skull is specialised and light, very like that of ''Ophiderpeton'', with the orbits, far forward, and the cheek region unossified (lacking bone). There are approximately 30 closely spaced teeth on the maxilla and dentary, and a sutural pattern of the skull closely resembles that of the Late Carboniferous aïstopod ''Oestocephalus''. There is no trace of limbs. However, unlike later members of the aïstopod lineage, the vertebrae still possess intercentra, and the pleurocentra are large. ''Lethiscus'' is the only representative of the family Lethiscidae. Owing to its early date, it has since its discovery been considered ancestral to later aïstopods, and more recent cladistic research (Anderson ''et al.'' 2003) confirms its position as the most basal (primitive) aistopod. ==References== * * Carroll, R.L (1988), ''Vertebrate Paleontology and Evolution'', WH Freeman & Co. pp.176-7 * Reisz, Robert (Biology 356 - Major Features of Vertebrate Evolution ) (online) * 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「Lethiscus」の詳細全文を読む スポンサード リンク
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