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Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, were quadrupedal, and became the largest animals to ever walk the Earth. The "prosauropods", which preceded the sauropods, were smaller and were often able to walk on two legs. The sauropodomorphs were the dominant terrestrial herbivores throughout much of the Mesozoic Era, from their origins in the mid-Triassic (approximately 230 Ma) until their decline and extinction at the end of the Cretaceous (approximately 66 Ma). ==Description== Sauropodomorphs were adapted to browsing higher than any other contemporary herbivore, giving them access to high tree foliage. This feeding strategy is supported by many of their defining characteristics, such as: a light, tiny skull on the end of a long neck (with ten or more elongated cervical vertebrae) and a counterbalancing long tail (with one to three extra sacral vertebrae). Their teeth were weak, and shaped like leaves or spoons (lanceolate or spatulate). Instead of grinding teeth, they had stomach stones (gastroliths), similar to the gizzard stones of modern birds and crocodiles, to help digest tough plant fibers. The front of the upper mouth bends down in what may be a beak. One of the earliest known sauropodomorphs, ''Saturnalia'', was small and slender (1.5 metres, or 5 feet long); but, by the end of the Triassic, they were the largest dinosaurs of their time, and in the Jurassic/Cretaceous they kept on growing. Ultimately the largest sauropods, like the ''Supersaurus'', '' Diplodocus hallorum'', and ''Argentinosaurus'', reached 30–40 metres (100–130 ft) in length, and 60,000–100,000 kilograms (65–110 US short tons) or more in mass. Initially bipedal, as their size increased they evolved to become graviportal quadrupeds (like elephants). The early sauropodomorphs were most likely omnivores as their shared common ancestor with the other saurischian lineage (the theropods) was a carnivore. Therefore their evolution to herbivory went hand in hand with their increasing size and neck length. They also had large nostrils (nares), and retained a thumb (pollex) with a big claw which may have been used for defense — though their primary defensive adaptation was their extreme size. Comparisons between the scleral rings of several sauropodmorph genera (''Diplodocus'', ''Lufengosaurus'', ''Nemegtosaurus'', ''Plateosaurus'', and ''Riojasaurus'') and modern birds and reptiles suggest that they may have been cathemeral, active throughout the day at short intervals. Sauropodomorphs reached the age of sexual maturity well before they were fully-grown adults.〔Sander PM (2000) Long bone histology of the Tendaguru sauropods: implications for growth and biology. Paleobiology 26: 466–488.〕〔Griebeler EM, Klein N, Sander PM (2013) Aging, Maturation and Growth of Sauropodomorph Dinosaurs as Deduced from Growth Curves Using Long Bone Histological Data: An Assessment of Methodological Constraints and Solutions. ''PLoS ONE'' 8(6): e67012. 〕 A study by Griebeler et al. (2013) concluded that the maximum growth rates of Sauropodomorphs were comparable to those of precocial birds, and the black rhinoceros but lower than the growth rates of average mammals.〔 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「Sauropodomorpha」の詳細全文を読む スポンサード リンク
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