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Ichthyostega
''Ichthyostega'' (Greek: "fish roof") is an early tetrapod genus that lived at the end of the Upper Devonian period. It was a labyrinthodont, one of the first tetrapods in the fossil record. ''Ichthyostega'' possessed lungs and limbs that helped it navigate through shallow water in swamps. Though undoubtedly of amphibian build and habit, it is not considered a true member of the group in the narrow sense, as the first true amphibians appeared in the Carboniferous period. Until finds of other early tetrapods and closely related fishes in the late 20th century, ''Ichthyostega'' stood alone as the transitional fossil between fish and tetrapods, combining a fishlike tail and gills with an amphibian skull and limbs.
==Description==
''Ichthyostega'' was a fairly large animal, broadly built and about 1.5 m long. The skull was flat with dorsally placed eyes and armed with large labyrinthodont teeth. The posterior margin of the skull formed an operculum covering the gills. The spiracle was situated in an otic notch behind each eye.
The limbs were large compared to contemporary relatives, and it had seven digits on each hind limb. The exact number of digits on the forelimb is not yet known, since fossils of the manus (hand) have not been found.〔''Evolutionary developmental biology'', by Brian Keith Hall, 1998, ISBN 0-412-78580-3, (p. 262 )〕 Although the forelimbs have never been recovered, they are generally thought to have been larger than the rear limbs, perhaps as an aid to carrying its body out of the water.〔(【引用サイトリンク】url=http://www.prehistoric-wildlife.com/species/i/ichthyostega.html )〕 It had a fin containing fin rays on its tail.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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