Eutheria

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EutheriaToday Placentalia and Eutheria are considered the same group. But there are proposals of classification (McKenna & Bell's 1997) that differentiate between the two groups. is a taxon (specifically, an infraclass) nearly containing the placental mammals. The name itself means "true beasts". The closest living relatives of the eutheres are part of the subclass Marsupialia.

When Eutheria was introduced by Thomas Henry Huxley in 1880, he meant for it to be more broad in definition than its precursor Placentalia. However, the adjective placental is used almost universally to describe a placental mammal; placental mammals are rarely, if ever, referred to as eutheres. As a result, Placentalia remains the preferred choice for many scientists.

The majority of living mammals are placental: the other two extant groups are the Monotremata and the Marsupialia; there are other groups of extinct mammals. The Eutheria are distinguished from other mammals in that the fetus is nourished during gestation via a placenta while, in general, this is not the case with other mammals (Bandicoots are a conspicuous exception to this rule). They reproduce sexually, and the "child" is carried in the mother until fully developed. Eutheria mammals are viviparous. Some examples of Eutheria Mammals are simians and leopards. Only females carry a placenta. Eutherian mammals—of which human beings are a member—are found on all continents.

The earliest known euitheria species is Eomaia from the Lower Cretaceous of China. It is undoubtedly a member of eutheria, but the hips of the animal are too narrowly built to have allowed the birth of well-developed young. This strongly suggests that a placenta played little role in the development of young.

The Greek words Eu- and theria mean, in this case, the "genuine beasts".

See also: Mammal for classification.
See also: Theria, Metatheria

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