The pouch is the most distinctive feature of marsupials (subclass marsupialia), a clade of non-placental mammals endemic to Australia and America. The name derives from the Latin baby carriermeaning pouch, and consists of a fold of skin that covers the breasts and forms a receptacle where part of fetal development takes place. Only females have marsupials, with few exceptions such as the water owl (Chironectes minimus).
Marsupials and other mammals
All mammals have in common the presence of mammary glands that produce milk to feed the young. A first classification of mammals divides them into viviparous mammals and oviparous mammals. Oviparous mammals are known as prototherians (“first animals”) and are represented only by monotremes (platypuses, echidnas). viviparous mammals called ries are the most numerous and are believed to have evolved evolutionarily after the prototherians.
In oviparous mammals, the embryo develops inside an egg. In viviparous mammals, the embryo develops in the mother’s uterus and the female gives birth to more or less developed offspring. Depending on the level of development of the offspring at birth, two major groups of viviparous mammals can be distinguished: placental mammals (eutherians) and marsupials (metatheries).
Marsupials give birth to a young in a very early stage of development, practically in a fetal state. After birth, the embryo slides along a line of saliva that the mother makes with her tongue until it reaches the baby carrier, where it will remain for a while, feeding on the breasts until it reaches adequate maturity. The pouch is also used by the mothers of some species to transport the young, mainly as protection from predators.
GalleryKangaroo fetus suckling from pouch Baby kangaroo grazing from pouch
Stock market variations
The marsupium, or marsupial pouch, shows some variability between different marsupial species. For example, the quols (genus dasyurus) and the Tasmanian devil (Sarcophilus harrisii) have the pouch close to the vaginal cloaca and the young woman has to walk only a few centimeters to enter the pouch after delivery; once the chicks develop, they leave the pouch and do not return.
The pouch of kangaroos, on the other hand, opens horizontally at the top of the belly and the young after birth have to travel a relatively long distance. Also, kangaroos and other marsupials, eg kangaroos, allow their young to live in the pouch for a while after they are sufficiently developed to come out and lead an independent life; the chicks can go out and back into the pouch.
In wombats and marsupial moles, the pouch opens at the bottom and rear, allowing them to dig their burrows into the ground without making a mess and throwing debris at the developing young.
Some marsupials, such as fascogals or marsupial mice (genus Phascogale), do not have a permanent pouch but form temporary skin folds in the breast area, often referred to as a pseudo-marsupion during the breeding period.