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Eutheria (; from Greek εὐ-, eu- "true/good" and θηρίον, thēríon "beast" hence "true beasts") is one of two mammalian clades with extant members that diverged in the Early Cretaceous or perhaps the Late Jurassic. Except for the Virginia opossum, from North America, which is a metatherian, all mammals indigenous to Europe, Africa, Asia, and North America north of Mexico are eutherians. Extant eutherians, their last common ancestor, and all extinct descendants of that ancestor are members of Placentalia. Eutherians are distinguished from noneutherians by various phenotypic traits of the feet, ankles, jaws and teeth. All extant eutherians lack epipubic bones, which are present in all other living mammals (marsupials and monotremes). This allows for expansion of the abdomen during pregnancy. The oldest known eutherian species is ''Juramaia sinensis'', dated at from the Jurassic in China. Eutheria was named in 1872 by Theodore Gill; in 1880 Thomas Henry Huxley defined it to encompass a more broadly defined group than Placentalia.〔(Eutheria (Placental Mammals) by J David Archibald, San Diego State University, San Diego, California, USA. PDF file from sdsu.edu )〕 ==Characteristics== Distinguishing features are: *an enlarged malleolus ("little hammer") at the bottom of the tibia, the larger of the two shin bones. *the joint between the first metatarsal bone and the entocuneiform bone (the outermost of the three cuneiform bones) in the foot is offset farther back than the joint between the second metatarsal and middle cuneiform bones – in metatherians these joints are level with each other.〔 *various features of jaws and teeth.〔 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「eutheria」の詳細全文を読む スポンサード リンク
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