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Stegosauria
The Stegosauria is a group of herbivorous ornithischian dinosaurs that lived during the Jurassic and Cretaceous periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere, predominantly in what is now North America, Europe and China, though one species (''Kentrosaurus aethiopicus'') is known to have lived in Africa, and the stegosaurian material of ''Dravidosaurus'' occurs in India. Their geographical origins are unclear; the earliest unequivocal stegosaurian, ''Huayangosaurus taibaii'', lived in China.
Stegosaurians were armored dinosaurs (thyreophorans). Originally, they did not differ much from more primitive members of that group, being small, low-slung, running animals protected by armored scutes. An early evolutionary innovation was the development of tail spikes, or "thagomizers", as defensive weapons. Later species, belonging to a subgroup called the Stegosauridae, became larger, and developed long hindlimbs that no longer allowed them to run. This increased the importance of active defence by the thagomizer, which could ward off even large predators because the tail was in a higher position, pointing horizontally to the rear from the broad pelvis. Stegosaurids had complex arrays of spikes and plates running along their backs, hips and tails. Their necks became longer and their small heads became narrow, able to selectively bite off the best parts of cycads with their beaks. When these plant types declined in diversity, so did the stegosaurians, which largely became extinct during the first half of the Cretaceous period, aside from indian species that survived possibly to the Cretaceous-Paleogene extinction event.
The first stegosaurian finds in the early 19th century were fragmentary. Better fossil material, of the genus ''Dacentrurus'', was discovered in 1874 in England. Soon after, in 1877, the first nearly-complete skeleton was discovered in the USA. Professor Othniel Charles Marsh that year classified such specimens in the new genus ''Stegosaurus'', from which the group acquired its name, and which is still by far the most famous stegosaurian. During the latter half of the twentieth century, many important Chinese finds were made, representing about half of the presently known diversity of stegosaurians.
==Description==
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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