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''Jeholornis'' (meaning "Jehol bird") is a genus of avialans that lived between approximately 122 and 120 million years ago during the early Cretaceous Period in China. Fossil ''Jeholornis'' were first discovered in the Jiufotang Formation in Hebei Province, China (in what was previously Rehe Province, also known as Jehol—hence the name) and additional specimens have been found in the older Yixian Formation.〔Li, D., Sulliven, C., Zhou, Z. and Zhang, Z. (2010). "Basal birds from China: a brief review." ''Chinese Birds'', 1(2): 83-96 〕 ''Jeholornis'' had long tails and few small teeth, and were approximately the size of turkeys,〔Holtz, Thomas R. Jr. (2008) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages'' (Supplementary Information )〕 making them among the largest avialans known until the Late Cretaceous. Their diet included seeds of cycads, Ginkgo or similar plants. ==Description== ''Jeholornis'' were relatively large, primitive avialans, with a maximum adult length of up to 80 cm (2.6 ft).〔 Their skulls were short and high, similar to other primitive avialans like ''Epidexipteryx'' and to early oviraptorosaurs like ''Incisivosaurus''. The lower jaws were short, stout, and curved downward, possibly an adaptation for eating seeds.〔 ''Jeholornis prima'' lacked teeth in their upper jaws, and had only three small teeth in their lower jaws,〔 while ''J. palmapenis'' had a few teeth in the middle of the upper jaw (maxilla) but none in the front (premaxilla). The upper teeth of ''J. palmapenis'' seem to have been angled slightly forward as in some other basal avialans. The teeth in all three species were small, blunt and peg-like with no serrations.〔 Their arms were robust and longer than the legs, with relatively well-developed shoulder girdles indicating strong wing musculature. The wishbone (''furcula'') was U-shaped in ''J. prima'' and ''J. palmapenis'' but not in ''J. curvipes''. Their fingers were short compared to those of ''Archaeopteryx'' and also more robust. The lower legs were not particularly long, indicating that these animals were not specialized runners.〔 The first toe, or ''hallux'', which is reversed in modern birds and used to perch in trees, was only partially reversed in both ''Jeholornis'' species, pointing inward and slightly backward. The halluces of ''Jeholornis'' were short, but their claw was more strongly curved than those of the other toes. Unlike deinonychosaurs and some other Mesozoic avialans, the claw of the second toe was not enlarged relative to the other claws.〔 Their tail anatomy was more like those of dromaeosaurids than ''Archaeopteryx'', with more strongly interlocking vertebrae, and though they had a similar number of tail vertebrae (between 20 and 24) those of ''Jeholornis'' were much longer overall than those of ''Archaeopteryx''.〔 The only well-preserved tail feathers come from the type specimen of ''J. palmapenis''. A study by Erickson in 2009 has shown that ''Jeholornis'' (along with ''Archaeopteryx'') had relatively slow ontogenic development, i.e. they grew very slowly, compared to most modern birds, which grow very quickly. The living kiwi birds however, have slow development, and it has been speculated that ''Jeholornis'' could have had a metabolism similar to these.〔Turner A.H., Erickson G.M., Norell M. A. ''et al.'' (2009), ("Was Dinosaurian Physiology Inherited by Birds? Reconciling Slow Growth in ''Archaeopteryx''" ), ''Public Library of Science'' 4(10).〕 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「Jeholornis」の詳細全文を読む スポンサード リンク
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