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}} ''Apatosaurus'' (meaning "deceptive lizard" ) is a genus of extinct sauropod dinosaurs that lived in North America during the Late Jurassic period. Othniel Charles Marsh described and named the first-known species, ''A. ajax'' in 1877, and a second species, ''A. louisae'', was discovered and named by William H. Holland in 1916. They lived about 152 to 151 million years ago (mya), during the early Tithonian age, and are now known from fossils in the Morrison Formation of modern-day Colorado, Oklahoma, and Utah, in the United States. ''Apatosaurus'' had an average length of , and an average mass of at least . A few specimens indicate a maximum length up to 30% greater than average and a mass of . The cervical vertebrae of ''Apatosaurus'' are less elongated and more heavily constructed than those of ''Diplodocus'', a diplodocid like ''Apatosaurus'', and the bones of the leg are much stockier despite being longer, implying that ''Apatosaurus'' was a more robust animal. The tail was held above the ground during normal locomotion. ''Apatosaurus'' had a single claw on each forelimb and three on each hindlimb. The skull of ''Apatosaurus'', long thought to be similar to ''Camarasaurus'', is much more similar to that of ''Diplodocus''. ''Apatosaurus'' was a generalized browser that likely held its head elevated. To lighten its vertebrae, ''Apatosaurus'' had air sacs that made the bones internally full of holes. Like that of other diplodocids, its tail may have been used as a whip to create loud noises. The skull of ''Apatosaurus'' was confused with that of ''Camarasaurus'' and ''Brachiosaurus'' until 1909, when the holotype of ''A. louisae'' was found, and a complete skull just a few meters away from the front of the neck. Henry Fairfield Osborn disagreed with this association, and went on to mount a skeleton of ''Apatosaurus'' with a ''Camarasaurus'' skull cast. Until 1970, ''Apatosaurus'' skeletons were mounted with speculative skull casts, when McIntosh showed that more robust skulls assigned to ''Diplodocus'' were more likely from ''Apatosaurus''. ''Apatosaurus'' is a genus in the family Diplodocidae. It is one of the more basal genera, with only ''Amphicoelias'', and possibly a new, unnamed genus more primitive. While the subfamily Apatosaurinae was named in 1929, the group was not used validly until an extensive 2015 study. Only ''Brontosaurus'' is also in the subfamily, with the other genera being considered as synonyms or reclassified as diplodocines. ''Brontosaurus'' has long been considered a junior synonym of ''Apatosaurus''; its only species was reclassified as ''A. excelsus'' in 1903. However, the 2015 study concluded that ''Brontosaurus'' was a valid genus of sauropod distinct from ''Apatosaurus''. As it existed in North America during the late Jurassic, ''Apatosaurus'' would have lived aside dinosaurs such as ''Allosaurus'', ''Camarasaurus'', ''Diplodocus'', and ''Stegosaurus''. ==Description== ''Apatosaurus'' was a large, long-necked, quadrupedal animal with a long, whip-like tail. Its forelimbs were slightly shorter than its hindlimbs. Most size estimates are based on specimen CM 3018, the type specimen of ''A. louisae''. In 1936, this was measured to be , by measuring the vertebral column.〔 Current estimates are similar, which find the individual was long and had a mass of .〔〔〔 A 2015 study that estimated the mass of volumetric models of ''Dreadnoughtus'', ''Apatosaurus'', and ''Giraffatitan'' estimates CM 3018 at , similar in mass to ''Dreadnoughtus''.〔 Past estimates have put the creature's mass as high as .〔 Some specimens of ''A. ajax'' (like OMNH 1670) represent individuals 11–30% longer, suggesting masses twice that of CM 3018 or , potentially rivalling the largest titanosaurs.〔 The skull is small in comparison with the size of the animal. The jaws are lined with spatulate (chisel-like) teeth suited to a herbivorous diet.〔 The snout of ''Apatosaurus'' and similar diplodocoids are squared, with only ''Nigersaurus'' having a squarer skull.〔 The braincase of ''Apatosaurus'' is well preserved in specimen BYU 17096, which also preserved much of the skeleton. A phylogenetic analysis found that the braincase had a similar morphology to those of other diplodocoids.〔 Some skulls of ''Apatosaurus'' have been found still in articulation with their teeth. Those teeth that have the enamel surface exposed do not show any scratches on the surface; instead they display a sugary texture and little wear.〔 Like those of other sauropods, the neck vertebrae are deeply bifurcated; they carried neural spines with a large trough in the middle, resulting in a wide, deep neck.〔 The vertebral formula for the holotype of ''A. louisae'' is 15 cervicals, 10 dorsals, 5 sacrals, and 82 caudals. The caudal vertebra number may vary, even within species.〔 The cervical vertebrae of ''Apatosaurus'' and ''Brontosaurus'' are stouter and more robust than those of other diplodocids, were found to be most similar to ''Camarasaurus'' by Charles Whitney Gilmore.〔〔 In addition, they support cervical ribs that extend farther towards the ground than in diplodocines, and have the vertebrae and ribs narrower towards the top of the neck, making the neck nearly triangular in cross-section.〔 In ''Apatosaurus louisae'', the atlas-axis complex of the first cervicals is nearly fused. The dorsal ribs are not fused or tightly attached to their vertebrae, instead being loosely articulated.〔 ''Apatosaurus'' has ten dorsal ribs on either side of the body.〔 The large neck was filled with an extensive system of weight-saving air sacs. ''Apatosaurus'', like its close relative ''Supersaurus'', has neural tall spines, which make up more than half the height of the individual bones of its vertebrae. The shape of the tail is unusual for a diplodocid; it is comparatively slender because of the rapidly decreasing height of the vertebral spines with increasing distance from the hips. ''Apatosaurus'' also had very long ribs compared to most other diplodocids, giving it an unusually deep chest.〔 As in other diplodocids, the tail transformed into a whip-like structure towards its end.〔 The limb bones are also very robust.〔 Within Apatosaurinae, the scapula of ''Apatosaurus louisae'' is intermediate in morphology between those of ''A. ajax'' and ''Brontosaurus excelsus''. The arm bones are stout, so the humerus of ''Apatosaurus'' resembles that of ''Camarasaurus'', as well as ''Brontosaurus''. However, the humeri of ''Brontosaurus'' and ''A. ajax'' are more similar to each other than they are to ''A. louisae''. In 1936, Charles Gilmore noted that previous reconstructions of ''Apatosaurus'' forelimbs erroneously proposed that the radius and ulna could cross; in life they would have remained parallel.〔 ''Apatosaurus'' had a single large claw on each forelimb, a feature shared by all sauropods more derived than ''Shunosaurus''.〔〔 The first three toes had claws on each hindlimb. The phalangeal formula is 2-1-1-1-1, meaning the innermost finger (phalanx) on the forelimb has two bones and the next has one.〔 The single manual claw bone (ungual) is slightly curved and squarely truncated on the anterior end. The pelvic girdle includes the robust ilia, and the fused (co-ossified) pubes and ischia. The femora of ''Apatosaurus'' are very stout; some of the most robust femora of any member of Sauropoda. The tibia and fibula bones are different from the slender bones of ''Diplodocus'', but are nearly indistinguishable from those of ''Camarasaurus''. The fibula is longer and more slender than the tibia. The foot of ''Apatosaurus'' has three claws on the innermost digits; the digit formula is 3-4-5-3-2. The first metatarsal is the stoutest, a feature shared among diplodocids.〔〔 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「apatosaurus」の詳細全文を読む スポンサード リンク
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