noun, plural: eutherian mammals
Any from the group of mammals possessing chorioallantoic placenta (as opposed to other mammalian groups)
Mammals may be grouped according to placentation. Placenta surrounding the fetus is made up of a single maternal layer (i.e.endometrium), an outer embryonic layer (i.e. chorion), and an inner embryonic layer.
In eutherian mammals, the inner embryonic layer is allantoic membrane whereas in metatherian mammals, a vitelline membrane. During the early gestation the vitelline membrane in eutherians recedes quickly whereas the allantois expands (thus the name, chorioallantoic placenta).
Mammals that lack placenta belong to the group of prototherian mammals.
Word origin: Greek eu– (true) + therion (beast)