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''Nigersaurus'' (meaning "Niger reptile") is a genus of rebbachisaurid sauropod dinosaur that lived during the middle Cretaceous period, about 115 to 105 million years ago. It was discovered in the Elrhaz Formation in an area called Gadoufaoua, in the Republic of Niger. Fossils of this dinosaur were first described in 1976, but it was only named in 1999 after further and more complete remains were found and described. The genus contains a single species, ''Nigersaurus taqueti'', named after French palaeontologist Philippe Taquet, who discovered the first remains. ''Nigersaurus'' was long, which is small for a sauropod, and had a short neck. It weighed around four tonnes, comparable to a modern elephant. Its skeleton was highly pneumatised (filled with air spaces connected to air sacs), but the limbs were robustly built. Its skull was very specialised for feeding, with large fenestrae and thin bones. It had a wide muzzle filled with more than 500 teeth, which were replaced at a rapid rate: around every 14 days. The jaws may have borne a keratinous sheath. Unlike other tetrapods, the tooth-bearing bones of its jaws were rotated transversely relative to the rest of the skull, so that all of its teeth were located far to the front. The closest relatives of ''Nigersaurus'' are grouped within the subfamily Nigersaurinae of the family Rebbachisauridae, which is part of the sauropod superfamily Diplodocoidea. ''Nigersaurus'' was probably a browser, and fed with its head close to the ground. The region of its brain that detected smell was underdeveloped, although its brain size was comparable to that of other dinosaurs. There has been debate on whether its head was habitually held downwards, or horizontally like other sauropods. It lived in a riparian habitat, and its diet probably consisted of soft plants, such as ferns, horsetails, and angiosperms. It is one of the most common fossil vertebrates found in the area, and shared its habitat with other dinosaurian megaherbivores, as well as large theropods and crocodylomorphs. ==Description== Like all sauropods, ''Nigersaurus'' was a megafaunal quadruped with a small head, thick hind legs, and a prominent tail. Among that clade, ''Nigersaurus'' was fairly small, with a body length of only and a femur reaching only . It may have weighed around four tonnes, comparable to a modern elephant. It had a short neck for a sauropod, with thirteen cervical vertebrae. Nearly all rebbachisaurids had relatively short necks and a length of or less. The only member of the family that reached the size of larger sauropods was ''Rebbachisaurus''.〔 The presacral vertebrae (vertebrae before the sacrum) were heavily pneumatised to the point where the column consisted of a series of hollow "shells", each divided by a thin septum in the middle. It had little to no cancellous bone, making the centra thin bone plates filled with air spaces. The vertebral arches were so heavily pierced by extensions of the external air sacs that of their side walls little remained but thick intersecting laminae, the ridges between the pneumatic openings. The vertebrae of the tail, however, did have solid centra. The pelvic and pectoral girdle bones were very thin also, often only several millimetres thick. Like other sauropods, its limbs were robust, contrasting with the extremely lightweight construction of the rest of the skeleton. The limbs were not as specialised as the rest of the skeleton, and the front legs of ''Nigersaurus'' were about two-thirds the length of the back legs, as in most diplodocoids.〔.〕 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「Nigersaurus」の詳細全文を読む スポンサード リンク
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