Noun
all mammals except monotremes and marsupials
Source: WordNetTheir body is well-adapted to their habitat, although they share essential characteristics with other higher mammals ( Eutheria ): citation They have a streamlined shape, and their forelimbs are flippers. Source: Internet
The marsupials constitute the crown group of the Metatheria, and include all living metatherians as well as many extinct ones; the placentals are the crown group of the Eutheria. Source: Internet
In other words, it may be nested within Eutheria or it may be the basal extant group. Source: Internet