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Xixiasaurus
''Xixiasaurus'' is a genus of extinct troodontid dinosaur from the Late Cretaceous of modern-day China. It was first described as a new taxon in 2010. The type species is ''X. henanensis''. Fossils of ''Xixiasaurus'' were discovered in central China, in the Majiacun Formation of Henan, and are believed to have been from the Late Cretaceous (Coniacian-Campanian age, about 83 million years ago). The fossils were described by a team of Chinese scientists composed of a group from the Chinese Academy of Geological Sciences in Beijing and a second group from the Henan Geological Museum in Henan. They chose the name ''Xixiasaurus henanensis'', translating as "Henan Xixia lizard".
==Description==
''Xixiasaurus'' is a troodontid, a group of small, bird-like, gracile maniraptorans. All troodontids have many unique features of the skull, such as closely spaced teeth in the lower jaw, and large numbers of teeth. Troodontids have sickle-claws and raptorial hands, and some of the highest non-avian encephalization quotients, meaning they were behaviourally advanced and had keen senses.〔 ''Xixiasaurus'' is about long.〔 It is one of few troodontids that have no serrations on its teeth, similar to its closest relative ''Byronosaurus''. ''Xixiasaurus'' has fewer teeth than ''Byronosaurus'' and ''Mei'', but more than ''Sinornithoides'', ''Zanabazar'' and ''Saurornithoides''. Like ''Bryonosaurus'', the palate is extensive, and the teeth are heterodont.
''Xixiasaurus'' is known from a mostly complete skull, only lacking the posterior portion. The top of the snout is slightly displaced, but overall, the skull resembles ''Bryonosaurus''. As the nasal bones are very not and not completely fused, the holotype of ''Xixiasaurus'' may have died immature. Most of the braincase is preserved, as well as most teeth and all tooth sockets. Viewed from below, the tooth rows form a U-shaped curve. Some small pits are present of the lateral surface of the maxilla. The teeth on the maxilla are larger than those in the premaxilla. The hand and lower arm are also preserved. The claw of the first digit is very large, with a large flexor tubercle. The first phalanges of the first two digits are and long, respectively.〔
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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