Most mammals are viviparous and give birth to live young. Such mammals are therian mammals. Like all vertebrates, therian mammals have ovaries. However, therian mammals have two additional structures: the uterus and the vagina. Therian mammals can be split into two groups: placenta mammals and marsupials. Only two living species of mammals are not viviparous, and they are grouped together as montremes.
Therian Mammal: Viviparous mammal that may be either a marsupial or placental mammal.
Viviparous: The characteristic of giving birth to live offspring.
Uterus: Female reproductive organ in therian mammals where an embryo or fetus grows and develops until birth.
Vagina: Female reproductive organ that receives sperm during sexual intercourse and provides a passageway for a baby to leave the mother’s body during birth.
Placental Mammal: Therian mammal in which a placenta develops during pregnancy to sustain the fetus while it develops inside the mother’s uterus.
Placenta: Temporary organ that consists of a large mass of maternal and fetal blood vessels through which the mother’s and fetus’s blood exchange substances.
Marsupial: Therian mammal in which the embryo is born at an early, immature stage and completes its development outside the mother’s body in a pouch on her belly.
Monotreme: Type of mammal that reproduces by laying eggs.
Therian mammals have a uterus and a vagina. The embryo develops inside the uterus.
A few mammals are marsupials, where the young are born and then develop inside the pouch of a mother.
There are five living svpecies of non-therian
mammals called monotremes. Monotremes are mammals
that actually reproduce by laying eggs.