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theria
Theria (; Greek: ''θηρίον'', wild beast) is a subclass of mammals〔(【引用サイトリンク】 title=Subclass Theria )〕 that give birth to live young without using a shelled egg, consisting of the eutherians (including the placental mammals) and the metatherians (including the marsupials). The only omitted extant mammal group is the egg-laying monotremes.
The earliest known therian mammal fossil is ''Juramaia'', from the Middle Jurassic of China. However, molecular data suggests that therians may have originated even earlier, during the Early Jurassic.〔
Hugall, A.F. ''et al.'' (2007) Calibration choice, rate smoothing, and the pattern of tetrapod diversification according to the long nuclear gene RAG-1. ''Syst Biol.'' 56(4):543-63.
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==Taxonomy==
(詳細はIn the above system Theria is a subclass. Alternatively, in the system proposed by
McKenna and Bell (1997)〔McKenna, Malcolm C., and Bell, Susan K. 1997. ''Classification of Mammals Above the Species Level.'' Columbia University Press, New York, 631 pp. ISBN 0-231-11013-8〕 it is ranked as a supercohort under the subclass Theriiformes:
Another classification proposed by Luo et al. (2002)〔Luo, Z.-X., Z. Kielan-Jaworowska, and R. L. Cifelli. 2002. In quest for a phylogeny of Mesozoic mammals. Acta Palaeontologica Polonica, 47:1-78.〕 does not assign any rank to the taxonomic levels, but uses a purely cladistic system instead.
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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