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''Iguanodon'' ( ; meaning "iguana-tooth") is a genus of ornithopod dinosaur that existed roughly halfway between the first of the swift bipedal hypsilophodontids of the mid-Jurassic and the duck-billed dinosaurs of the late Cretaceous. While many species have been classified in the genus ''Iguanodon'', dating from the late Jurassic Period to the late Cretaceous Period of Asia, Europe, and North America, research in the first decade of the 21st century suggests that there is only one well-substantiated species: ''I. bernissartensis'', which lived from the late Barremian to the earliest Aptian ages (Early Cretaceous) in Belgium and possibly elsewhere in Europe, between about 126 and 125 million years ago. ''Iguanodon'' were large, bulky herbivores. Distinctive features include large thumb spikes, which were possibly used for defense against predators, combined with long prehensile fifth fingers able to forage for food. The genus was named in 1825 by English geologist Gideon Mantell, based on fossil specimens that are now assigned to different genera and species. ''Iguanodon'' was the second type of dinosaur formally named based on fossil specimens, after ''Megalosaurus''. Together with ''Megalosaurus'' and ''Hylaeosaurus'', it was one of the three genera originally used to define Dinosauria. The genus ''Iguanodon'' belongs to the larger group Iguanodontia, along with the duck-billed hadrosaurs. The taxonomy of this genus continues to be a topic of study as new species are named or long-standing ones reassigned to other genera. Scientific understanding of ''Iguanodon'' has evolved over time as new information has been obtained from fossils. The numerous specimens of this genus, including nearly complete skeletons from two well-known bonebeds, have allowed researchers to make informed hypotheses regarding many aspects of the living animal, including feeding, movement, and social behaviour. As one of the first scientifically well-known dinosaurs, ''Iguanodon'' has occupied a small but notable place in the public's perception of dinosaurs, its artistic representation changing significantly in response to new interpretations of its remains. ==Description== ''Iguanodon'' were bulky herbivores that could shift from bipedality to quadrupedality. The only well-supported species, ''I. bernissartensis'', is estimated to have weighed about 3.08 tonnes (3.4 tons) on average, and measured about 10 metres long (33 ft) as an adult, with some specimens possibly as long as 13 metres (43 ft). These animals had large, tall but narrow skulls, with toothless beaks probably covered with keratin, and teeth like those of iguanas, but much larger and more closely packed.〔 The arms of ''I. bernissartensis'' were long (up to 75% the length of the legs) and robust,〔 with rather inflexible hands built so that the three central fingers could bear weight.〔 The thumbs were conical spikes that stuck out away from the three main digits. In early restorations, the spike was placed on the animal's nose. Later fossils revealed the true nature of the thumb spikes, although their exact function is still debated. They could have been used for defense, or for foraging for food. The little finger was elongated and dextrous, and could have been used to manipulate objects. The phalangeal formula is 2-3-3-2-4, meaning that the innermost finger (phalange) has two bones, the next has three, etc.〔Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. 560 pp. ISBN 1–4051–3413–5.〕 The legs were powerful, but not built for running, and each foot had three toes. The backbone and tail were supported and stiffened by ossified tendons, which were tendons that turned to bone during life (these rod-like bones are usually omitted from skeletal mounts and drawings).〔 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「Iguanodon」の詳細全文を読む スポンサード リンク
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