page_title: Nigersaurus
section_title: Skull
hierarchical_section_title: Nigersaurus / Description / Skull
caption_attribution_description: Italiano: Fossil of Nigersaurus, an extinct reptile- Took the photo at Museo di Storia Naturale di Venezia
context_page_description: Nigersaurus 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 Nigersaurus taqueti in 1999, after further and more complete remains were found and described. The genus name means "Niger reptile", and the specific name honours the palaeontologist Philippe Taquet, who discovered the first remains.
  Small for a sauropod, Nigersaurus was about 9 m long, and had a short neck. It weighed around 4 t, comparable to a modern elephant. Its skeleton was highly pneumatised, 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.
context_section_description: The skull of Nigersaurus was delicate, with the four side fenestrae (openings in the skull) larger than in other sauropodomorphs. The total area of bone connecting the muzzle to the back of the skull was only 1.0 cm² (0.16 sq in). These connecting struts of bones were usually less than 2 mm (0.08 in) thick. Despite this, the skull was resistant to the sustained shearing of the teeth. Another unique trait it had among sauropodomorphs was a closed supratemporal fenestra. The nasal openings, the bony nostrils, were elongated. Though the nasal bones are not completely known, it appears the front margin of the bony nostril was closer to the snout than in other diplodocoids. The snout was also proportionately shorter, and the tooth row was not at all prognathous, the snout tip not protruding relative to the remainder of the tooth series. The maxillary tooth row was in its entirety transversely rotated, its normal rear 90° everted towards the front. This was matched by an identical rotation of the dentary of the lower jaw. As a result, no other tetrapod had all of its teeth located as far to the front as Nigersaurus.
  The slender teeth had slightly curved crowns, which were oval in cross-section. The teeth in the lower jaw may have been 20–30% smaller than those in the upper jaw, but few are known, and they are of uncertain maturity. Apart from this, the teeth were identical. Under each active tooth there was a column of nine replacement teeth within the jaw. With 68 columns in the upper jaws and 60 columns in the lower jaws, these so-called dental batteries (also present in hadrosaurs and ceratopsians) comprised a total of more than 500 active and replacement teeth. Dental batteries erupted in unison, not each column individually. The enamel on the teeth of Nigersaurus was highly asymmetrical, ten times thicker on the outwards facing side than on the inner side. This condition is otherwise known only in advanced ornithischians.
  Nigersaurus did not exhibit the same modifications seen in the jaws of other dinosaurs with dental batteries, or mammals with elaborate chewing functions. The lower jaw was S-shaped and divided into the subcylindrical transverse ramus, which contained the teeth, and the back ramus, which was more lightweight and was the location for most of the muscle attachments. The jaws also contained several fenestrae, including three that are not present in other sauropods. The front ends of the jaws had grooves that indicate the presence of a keratinous (horny) sheath. Nigersaurus is the only known tetrapod animal to have had jaws wider than the skull and teeth that extended laterally across the front. The snout was even broader than those of the "duck-billed" hadrosaurs.
caption: Teeth at different growth stages, Museo di Storia Naturale di Venezia
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