<Li> Placentalia (placental mammals) </Li> <P> Eutheria (/ juː ˈθɪəriə /; from Greek εὐ -, eu - "good" or "right" 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 post-Miocene 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 . </P> <P> 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 . </P> <P> The oldest known eutherian species is Juramaia sinensis, dated at 160 million years ago from the Jurassic in China . </P>

Why do humans belong to the subclass eutheria
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