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''Majungasaurus'' (; "Mahajanga lizard") is a genus of abelisaurid theropod dinosaur that lived in Madagascar from 70 to 66 million years ago, at the end of the Cretaceous Period. The genus contains a single species, ''Majungasaurus crenatissimus''. This dinosaur was briefly called ''Majungatholus'', a name which is now considered a junior synonym of ''Majungasaurus''. Like other abelisaurids, ''Majungasaurus'' was a bipedal predator with a short snout. Although the forelimbs are not completely known, they were very short, while the hindlimbs were longer and very stocky. It can be distinguished from other abelisaurids by its wider skull, the very rough texture and thickened bone on the top of its snout, and the single rounded horn on the roof of its skull, which was originally mistaken for the dome of a pachycephalosaur. It also had more teeth in both upper and lower jaws than most abelisaurids. Known from several well-preserved skulls and abundant skeletal material, ''Majungasaurus'' has recently become one of the best-studied theropod dinosaurs from the Southern Hemisphere. It appears to be most closely related to abelisaurids from India rather than South America or continental Africa, a fact that has important biogeographical implications. ''Majungasaurus'' was the apex predator in its ecosystem, mainly preying on sauropods like ''Rapetosaurus'', and is also one of the few dinosaurs for which there is direct evidence of cannibalism. == Description == ''Majungasaurus'' was a medium-sized theropod that typically measured in length, including its tail. Fragmentary remains of larger individuals indicate that some adults reached lengths of more than . Sampson and Witmer estimated an average weight for an adult ''Majungasaurus'' of .〔 The specimen they based it on (FMNH PR 2100) was not the largest one discovered. Larger specimens of ''Majungasaurus crenatissimus'' could have been similar in size to its relative ''Carnotaurus'',〔 which has been estimated to weigh . The skull of ''Majungasaurus'' is exceptionally well-known compared to most theropods and generally similar to that of other abelisaurids. Like other abelisaurid skulls, its length was proportionally short for its height, although not as short as in ''Carnotaurus''. The skulls of large individuals measured long. The tall premaxilla (frontmost upper jaw bone), which made the tip of the snout very blunt, was also typical of the family. However, the skull of ''Majungasaurus'' was markedly wider than in other abelisaurids. All abelisaurids had a rough, sculptured texture on the outside faces of the skull bones, and ''Majungasaurus'' was no exception. This was carried to an extreme on the nasal bones of ''Majungasaurus'', which were extremely thick and fused together, with a low central ridge running along the half of the bone closest to the nostrils. A distinctive dome-like horn protruded from the fused frontal bones on top of the skull as well. In life, these structures would have been covered with some sort of integument, possibly made of keratin. Computed tomography (CT scanning) of the skull shows that both the nasal structure and the frontal horn contained hollow sinus cavities, perhaps to reduce weight.〔 The teeth were typical of abelisaurids in having short crowns, although ''Majungasaurus'' bore seventeen teeth in both the maxilla of the upper jaw and the dentary of the lower jaw, more than in any other abelisaurid except ''Rugops''. The postcranial skeleton of ''Majungasaurus'' closely resembles those of ''Carnotaurus'' and ''Aucasaurus'', the only other abelisaurid genera for which complete skeletal material is known. ''Majungasaurus'' was bipedal, with a long tail to balance out the head and torso, putting the center of gravity over the hips. Although the cervical (neck) vertebrae had numerous cavities and excavations (pleurocoels) to reduce their weight, they were robust, with exaggerated muscle attachment sites and ribs that interlocked for strength. Ossified tendons attached to the cervical ribs, giving them a forked appearance, as seen in ''Carnotaurus''. All of these features resulted in a very strong and muscular neck. Uniquely, the cervical ribs of ''Majungasaurus'' had long depressions along the sides for weight reduction. The humerus (upper arm bone) was short and curved, closely resembling those of ''Aucasaurus'' and ''Carnotaurus''. Also like related dinosaurs, ''Majungasaurus'' had very short forelimbs with four extremely reduced digits, first reported with only two very short external fingers and no claws. The hand and finger bones of ''Majungasaurus'', like other majungasaurines, lacked the characteristic pits and grooves where claws and tendons would normally attach, and its finger bones were fused together, indicating that the hand was immobile. In 2012, a better specimen was described, showing that the lower arm was robust, though short, and that the hand contained four metatarsals and four, probably inflexible and very reduced, fingers, with small claws on the second and third finger. The phalanx formula was 1-2-2-1-0. Like other abelisaurids, the hindlimbs were stocky and short compared to body length. The tibia (lower leg bone) of ''Majungasaurus'' was even stockier than that of its relative ''Carnotaurus'', with a prominent crest on the knee. The astragalus and calcaneum (ankle bones) were fused together, and the feet bore three functional digits, with a smaller first digit that did not contact the ground. 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「Majungasaurus」の詳細全文を読む スポンサード リンク
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