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''Deinocheirus'' ( ) is a genus of large ornithomimosaur (ostrich dinosaur) that lived during the Late Cretaceous around 70 million years ago. In 1965, a pair of large arms, shoulder girdles, and a few other bones of a new dinosaur were first discovered in the Nemegt Formation of Mongolia. In 1970, this specimen became the holotype of the only species within the genus, ''Deinocheirus mirificus''; the genus name is Greek for "horrible hand". No further remains were discovered for almost fifty years, and its nature remained a mystery. Two more complete specimens were described in 2014, which shed light on many aspects of the animal. Parts of these new specimens had been looted from Mongolia some years before, but were repatriated in 2014. ''Deinocheirus'' was an unusual ornithomimosaur, the largest of the clade at long, and weighing . Though it was a bulky animal, it had many hollow bones which saved weight. The arms were among the largest of any bipedal dinosaurs at long, with large, blunt claws on its three-fingered hands. The legs were relatively short, and bore blunt claws. Its vertebrae had tall neural spines that formed a "sail" along its back. The tail ended in pygostyle-like vertebrae, which indicate the presence of a fan of feathers. The skull was long, with a wide bill and a deep lower jaw, similar to those of hadrosaurs. The classification of ''Deinocheirus'' was long uncertain, and it was initially placed in the theropod group carnosauria, but similarities with ornithomimosaurians were soon noted. After more complete remains were found, ''Deinocheirus'' was shown to be a primitive ornithomimosaurian, most closely related to the smaller genera ''Garudimimus'' and ''Beishanlong'', together forming the family Deinocheiridae. Members of this group were not adapted for speed, unlike other ornithomimosaurs. ''Deinocheirus'' is thought to have been omnivorous; its skull shape indicates a diet of plants, fish scales were found in association with one specimen and gastroliths were also present in the stomach region of the specimen. The large claws may have been used for digging and gathering plants. Bite marks on ''Deinocheirus'' bones have been attributed to the tyrannosaurid ''Tarbosaurus''. ==Description== ''Deinocheirus'' was the largest ornithomimosaurian (ostrich dinosaur); the largest known specimen measured up to long, with an estimated weight of . The two other known specimens are smaller, the holotype by 6%, and the smallest, a subadult, by 74%.〔 When only the incomplete holotype arms were known, various sizes were extrapolated from them by different methods. A 2010 study estimated the hip height of ''Deinocheirus'' to be .〔 The weight had previously been estimated between to . Enormous sizes were also suggested by comparing the arms with those of tyrannosaurs, even though members of that group have very small arms in proportion to their body size.〔〔〔 ''Deinocheirus'' and ''Therizinosaurus'' possessed the longest forelimbs known for any bipedal dinosaurs.〔 The holotype forelimbs measure long — the humerus (upper arm bone) is , the ulna , and the hand is — including the long recurved claws. Each scapulocoracoid of the shoulder girdle has a length of . Each half of the paired ceratobranchialia measure . The shoulder-blade was long and narrow, and the deltopectoralis crest was pronounced and triangular. The upper arm (humerus) was relatively slender, and only slightly longer than the hand. The ulna and radius (lower arm bones) were elongate and not firmly connected to each other in a syndesmosis. The metacarpus was long compared to the fingers. The three fingers were about equal in length, the first being the stoutest and the second the longest. Various rough areas and impressions on the forelimbs indicate the presence of powerful muscles. Most articular surfaces of the arm bones were deeply furrowed, indicating that the animal had thick pads of cartilage between the joints. Though the arms of ''Deinocheirus'' were large, the ratio between them and the shoulder girdle was less than that of the smaller ornithomimosaur ''Ornithomimus''.〔 The arm bones of ''Deinocheirus'' were similar in proportions to those of the small theropod ''Compsognathus''.〔 The wishbone (furcula), an element not known from any other ornithomimosaurs, was U-shaped. The hindlimbs were relatively short, and the thigh bone (femur) was longer than the shin bone (tibia), as is common for large animals. The metatarsus was short and not arctometatarsalian, as in most other theropods. The claw bones of the feet were blunt and broad-tipped instead of tapered, unlike other theropods, but resembled the unguals of large ornithischian dinosaurs. The proportions of the toe bones resembled those of tyrannosaurs, due to the large weight they had to bear.〔 Though ''Deinocheirus'' was a bulky animal, its dorsal ribs were tall and relatively straight, indicating that the body was narrow.〔 The ten neck vertebrae were low and long, and progressively shorter backwards from the skull. This resulted in a more S-curved neck than seen in other ornithomimosaurs, due to the larger skull. The neural spines of the twelve back vertebrae became increasingly longer from front to back, the last one being 8.5 times the height of the centrum part. This is almost the same as the highest ratio in the neural spines of the theropod ''Spinosaurus''. The neural spines had a system of ligaments, which were probably used to support the abdomen by attaching to the hips and hind legs.〔 Together, the neural spines formed a tall "sail" along the lower back, hips, and base of the tail, somewhat similar to that of ''Spinosaurus''.〔 All the vertebrae were highly pneumatised by air sacs, except for the atlas bone and the hindmost tail vertebrae, and were connected to the respiratory system. The back vertebrae were as pneumatised as those of sauropod dinosaurs, and had an extensive system of depressions. These adaptations may be correlated with gigantism, as they reduce weight. The six vertebrae of the sacrum were also tall and pneumatised, and all but the first one were fused together at the top, their neural spines forming a neural plate. The ilium, the top hip bone, was also partially pneumatised close to the sacral vertebrae. Part of the pelvis was hypertrophied (enlarged) compared to other ornithomimosaurs, to support the weight of the animal with strong muscle attachments. The front hip bones tilted upwards in life. The tail of ''Deinocheirus'' ended in at least two fused vertebrae, which were described as similar to the pygostyle of oviraptorosaurian and therizinosauroid theropods. Ornithomimosaurs are known to have had pennaceous feathers, so this feature suggests that they might have had a fan of feathers at the tail end.〔 The only known skull, belonging to the largest specimen, measures from the premaxilla at the front to the back of the occipital condyle. The widest part of the skull behind the eyes is only wide in comparison. The skull was similar to those of other ornithomimosaurs in being low and narrow, but differed in that the snout was more elongated. The skull bone walls were rather thin, about . It had a rounded, flattened beak, which would have been covered by keratin in life. The nostrils were turned upwards, and the nasal bone was a narrow strap that extended up above the eye sockets. The outer diameter of the sclerotic rings in the eyes was small, , compared to the size of the skull. The lower temporal fenestrae, openings behind the eyes, were partially closed off by the jugal bones, similar to ''Gallimimus''. The jaws were toothless and down-turned, and the lower jaw was very massive and deep compared to the slender and low upper jaw. The relative size of the lower jaw was closer to that of tyrannosaurids than to other ornithomimosaurs. The snout was spatulate (flared outwards to the sides) and wide, which is wider than the skull roof.〔 This shape is similar to the snout of duck-billed hadrosaurids.〔 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「Deinocheirus」の詳細全文を読む スポンサード リンク
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