Menstruation (mammal)
Menstruation in mammals is the shedding of the uterine lining (endometrium). It occurs on a regular basis in uninseminated sexually reproductive-age females of certain mammal species.
Placentophagy
There is also a school of thought that holds that placentophagy naturally occurred to hide any trace of childbirth from predators in the wild. Many placental mammals participate in placentophagy, including herbivores; exceptions include mainly humans, Pinnipedia, Cetacea, and camels. Placentophagy has been observed in Insectivora, Rodentia, Chiroptera, Lagomorpha, Carnivora, Perissodactyla, Artiodactyla (with the camel as a noted exception), and Primates. Marsupials, which are an order of metatherian (pouched) mammals, resorb rather than deliver the placenta, and therefore cannot engage in placentophagia; they do, however, vigorously lick birth fluids as they are excreted.