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''Castorocauda'' is a genus of small, semi-aquatic mammal relatives living in the Jurassic period, around 164 million years ago, found in lakebed sediments of the Daohugou Beds of Inner Mongolia. It contains the single species ''Castorocauda lutrasimilis''. They were highly specialized, with adaptations evolved convergently with those of modern semi-aquatic mammals such as beavers, otters, and the platypus. ==Classification== ''Castorocauda lutrasimilis'' is a member of the order Docodonta, which is a wholly extinct group of Mammaliaformes. It is not considered to be a mammal by the crown group definition, which takes the mammals to be the group containing the most recent common ancestor of all living mammals (the monotremes, placentals, and marsupials) and its descendants. Many writers, however, do not define Mammalia as a crown group; Kielan-Jaworowska ''et al.'' (2004), for example, defines Mammalia as the group originating with the last common ancestor of ''Sinoconodon'' and living mammals, a definition that includes Docodonta. A ''Castorocauda'' fossil was discovered in 2004 in the fossil-rich beds of Liaoning province, China; it was reported in the journal ''Science'' by an international team led by Qiang Ji of Nanjing University. The fossil was so well preserved that an important feature of its soft anatomy — hair — was preserved. Hair is present in all modern mammals and is therefore assumed, under principles of maximum parsimony, to have been present in all descendants of the last common ancestor of ''Castorocauda'' and today's mammals, including crown mammals and other docodonts. The hair appears to have been a very advanced dense pelage including guard hairs and underfur. The tiny auditory ossicles of the middle ear and associated areas were also well preserved in this ''Castorocauda'' fossil. Features of these bones confirms the evolutionary position of docodonts as more closely related to crown-group mammals than is ''Morganucodon''. They are, however, less closely related to living mammals than is ''Hadrocodium''. Among docodonts, ''Castorocauda'' appears to have been related to ''Krusatodon'' and ''Simpsonodon'', both European animals. This may be evidence that Europe and Asia underwent a faunal interchange in the Middle Jurassic. The two continents would later be separated by the Turgai Strait. 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「Castorocauda」の詳細全文を読む スポンサード リンク
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