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''Eusthenopteron'' is a genus of prehistoric sarcopterygian (often called lobe-finned fishes) which has attained an iconic status from its close relationships to tetrapods. Early depictions of this animal show it emerging onto land, however paleontologists now widely agree that it was a strictly aquatic animal.〔M. Laurin, F. J. Meunier, D. Germain, and M. Lemoine 2007. (A microanatomical and histological study of the paired fin skeleton of the Devonian sarcopterygian ''Eusthenopteron foordi ). Journal of Paleontology'' 81: 143–153.〕 The genus ''Eusthenopteron'' is known from several species that lived during the Late Devonian period, about 385 million years ago. ''Eusthenopteron'' was first described by J. F. Whiteaves in 1881, as part of a large collection of fishes from Miguasha, Quebec. Some 2,000 ''Eusthenopteron'' specimens have been collected from Miguasha, one of which was the object of intensely detailed study and several papers from the 1940s to the 1990s by paleoichthyologist Erik Jarvik.〔 〕 ==Description== Anatomically, ''Eusthenopteron'' shares many unique features in common with the earliest known tetrapods. Largest individuals grew up to 1.8 m (~ 6 ft) in length.〔http://www.prehistoric-wildlife.com/species/e/eusthenopteron.html〕 It shares a similar pattern of skull roofing bones with forms such as Ichthyostega and Acanthostega. ''Eusthenopteron'', like other tetrapodomorph fishes, had internal nostrils, (or a choana) which are one of the defining traits of tetrapodomorphs (including tetrapods). It also had labyrinthodont teeth, characterized by infolded enamel, which characterizes all of the earliest known tetrapods as well. Like other fish-like sarcopterygians, ''Eusthenopteron'' possessed a two-part cranium, which hinged at mid-length along an intracranial joint. ''Eusthenopterons notoriety comes from the pattern of its fin endoskeleton, which bears a distinct humerus, ulna, and radius (in the fore-fin) and femur, tibia, and fibula (in the pelvic fin). These appendicular long bones had epiphyseal growth plates that allowed substantial longitudinal growth through endochondral ossification, as in tetrapod long bones.〔M. Laurin, F. and J. Meunier 2012. A microanatomical and histological study of the fin long bones of the Devonian sarcopterygian ''Eusthenopteron foordi. Acta Zoologica'' 93: 88–97.〕 These six appendicular bones also occur in tetrapods and are a synapomorphy of a large clade of sarcopterygians, possibly Tetrapodomorpha (the humerus and femur are present in all sarcoptergyians). Similarly, its elasmoid scales lack superficial odontodes composed of dentine and enamel; this loss appears to be a synapomorphy with more crownward tetrapodomorphs.〔Zylberberg, L., Meunier, F. J. and Laurin, M. 2010. A microanatomical and histological study of the postcranial dermal skeleton in the Devonian sarcopterygian ''Eusthenopteron foordi. (Acta Palaeontologica Polonica )'' 55: 459–470.〕 The earliest known fossilised evidence of bone marrow has been found in ''Eusthenopteron'', which may be the origin of bone marrow in tetrapods.〔Sanchez S, Tafforeau P and Ahlberg P E (2014) ("The humerus of Eusthenopteron: a puzzling organization presaging the establishment of tetrapod limb bone marrow" ) ''Proceedings of the Royal Society B: Biological Sciences'', 281 (1782): 20140299. 〕 ''Eusthenopteron'' differs significantly from some later Carboniferous tetrapods in the apparent absence of a recognized larval stage and a definitive metamorphosis.〔Schultze, H.-P. 1984. Juvenile specimens of ''Eusthenopteron foordi'' Whiteaves, 1881 (Osteolepiform rhipidistian, Pisces) from the Late Devonian of Miguasha, Quebec, Canada. ''Journal of Vertebrate Paleontology'' 4: 1-16.〕 In even the smallest known specimen of ''Eusthenopteron foordi '' (at 29 mm), the lepidotrichia cover all of the fins, which does not happen until after metamorphosis in genera like ''Polyodon''. This might indicate that ''Eusthenopteron'' developed directly, with the hatchling already attaining the general body form of the adult (Cote et al., 2002). 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「Eusthenopteron」の詳細全文を読む スポンサード リンク
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