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''Yanoconodon'' is a monotypic genus of extinct early mammal whose representative species ''Yanoconodon allini'' lived during the Mesozoic in what is now China. It is considered to be a transitional fossil due to the formation of its middle ear, which is a cross between those of modern mammals and their nearest relatives, the mammaliaformes. It was found in the Qiaotou member of the Huajiying Formation (which the original authors considered part of the Yixian Formation) of Hebei Province, China, and is therefore of uncertain age. The Qiaotou Member may correlate with the more well-known Early Cretaceous Yixian Formation, and so probably dates to around 122 Ma ago.〔Jin, F., Zhang, F.C., Li, Z.H., Zhang, J.Y., Li, C. and Zhou, Z.H. (2008). "On the horizon of ''Protopteryx'' and the early vertebrate fossil assemblages of the Jehol Biota." ''Chinese Science Bulletin'', 53(18): 2820-2827.〕 ''Yanoconodon'' was a Eutriconodont, a group synonymous to the Triconodonts which lived during the time of the dinosaurs. Indeed, some such as ''Repenomamus'' grew so large that they were able to eat small dinosaurs in some cases.〔Hu, Y., Meng, J., Wang, Y. & Li, C. (2005). ''Large Mesozoic mammals fed on young dinosaurs''. Nature. Vol 433, 12 January 2005, Number 7022, pp91-178, . (See commentary on this article (Retrieved 25/6/2007) ).〕 In particular, ''Yanoconodon'' is considered to be closely related to ''Jeholodens''.〔Luo, Z., Chen, P., Li, G., & Chen, M. (2007). ''(A new eutriconodont mammal and evolutionary development in early mammals )''. Nature. Vol 446, 15 March 2007, .〕 ''Yanoconodons name is composed of two elements: 'Yan' is taken from the Yan Mountains in the north of the Hebei Province near where the holotype of ''Yanoconodon'' was found; 'Conodon' is an often used as a mammalian taxonomic suffix meaning 'cuspate tooth'. Its species name, "allini," is derived from mammalian researcher Edgar Allin, who was notable for his research on the mammalian middle ear.〔〔''(Paleontologists Discover New Mammal from Mesozoic Era )'' at (www.physorg.com ) - Retrieved 25/6/2007.〕 ''Yanoconodon'' was a small mammal, barely 5 inches (13 centimetres) long. It was lightly built and probably fed on insects, worms and other invertebrates. Like other Eutriconodonts, ''Yanoconodon'' probably hunted at night out of the danger posed by predatory dinosaurs during the day. Like most early mammals, ''Yanoconodon'' had short, sprawling legs and claws that were most likely used for burrowing underground or digging.〔〔 The holotype fossil of ''Yanoconodon'' was excavated in the Yan Mountains about 300 kilometres from Beijing. It is so well preserved that scientists were able to examine tiny bones of the middle ear. The intermediate anatomy of the middle ear of ''Yanocodon'' is said to be a "Rosetta Stone"〔 of mammalian middle ear evolution. In addition, Yanocodon had lumbar ribs, a particularly rare feature in mammals today. The closely related Eutriconodont ''Jeholodens'' lacks these lumbar ribs, and it has been suggested that this morphological difference is due to changes in the Hox genes, specifically in the ''Hox10'' group.〔 In mice, a triple mutation knocking out all ''Hox10'' genes leads to the presence of lumbar ribs,〔Deneen M. Wellik and Mario R. Capecchi. (2003). ''Hox10 and Hox11 Genes Are Required to Globally Pattern the Mammalian Skeleton''. Science, Vol. 301, 18 July 2003, no. 5631, pp. 363 - 367, .〕 supporting the theory that these genes have evolved the ability to repress the ancestral Lumbar morphology seen in the Eutriconodonts. ==References== 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「Yanoconodon」の詳細全文を読む スポンサード リンク
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