The term marsupial refers primarily to a particular type of mammal, also referred to as metatherian mammals. There are around two hundred and eighty species of marsupial divided into eighteen families. They can be found in North and South America, Eastern Indonesia, Papua New Guinea, the Solomon Islands, Australia, and New Zealand.
Most mammals are placental mammals and a developing embryo is nourished within the mother's womb by a placenta that transfers nutrients from the mother's blood stream to that of the embryo. Marsupials instead have a yolk-like placenta, which provides limited nourishment. Their gestation period is quite short, ranging from 8 to 43 days. When a marsupial gives birth, the baby has barely developed beyond the embryonic stage and must climb from the birth canal to the mother's teats (usually in a pouch or 'marsupium') to gain nourishment and grow further.
The main advantage for marsupials is that birth is not traumatic to the mother. Mothers face practically no danger of complications in the birthing process. This is countered by the newborn being almost entirely helpless and the size of a litter being limited by the number of teats that the species carries.
Like other mammals, marsupials have hair and nurse their young. Many species of marsupial will nurse right up until the child has become a full adult. Although marsupial mammals diverged from placental mammals about 120 million years ago, they have evolved similar forms for the same ecological niches. Examples can be found of grazing marsupials, burrowing marsupials, and even ant-eating marsupials. Fossil records have been found of marsupial lions, rhinoceros-like herbivores, and 10 foot tall kangaroos.
During the Mesozoic era, marsupials were very common to North America and outnumbered placental mammals. After the Tertiary period, most became extinct with the exception of the opossum. South America was also home to numerous marsupials similar to the possum until placental mammals spread across the continent in the late Miocene era. Australia is home to most of today's marsupial animals. The various species include kangaroos, koalas, Tasmanian devils, and wombats. Some species, such as the marsupial wolf, have become extinct as recently as the 1950's.
In zoology, the term marsupial is sometimes given to an animal displaying a pouch for carrying its young. One example in particular is Gastrotheca marsupiata, the Australian Marsupial Frog.
The Marsupial Mammal families:
Sources: http://www.marsupialsociety.org.au, http://www.marsupialcrc.com.au, http://animaldiversity.ummz.umich.edu/
- Acrobatidae: Feathertail glider - Australia
- Burramyidae: Pygmy Possums - Australia, South West Pacific Islands
- Caenolestidae: Shrew Opossums - Americas
- Dasyuridae: Dasyurids, Quolls, Dunnarts, Marsupial Mice - Australia, South West Pacific Islands
- Didelphidae: Opossums - Americas
- Macropodidae: Kangaroos and Wallabies - Australia, South West Pacific Islands
- Myrmecobiidae: Numbat - Australia
- Notoryctidae: Marsupial Moles - Australia
- Peramelidae: Bandicoots - Australia
- Peroryctidae: Spiny bandicoots - Australia, South West Pacific Islands
- Petauridae: Gliders - Australia, South West Pacific Islands
- Phalangeridae: Large Possums - Australia, South West Pacific Islands
- Phascolarctidae: Koala - Australia
- Potoroidae: Rat-kangaroos - Australia
- Pseudocheiridae: Ringtail Possums - Australia, South West Pacific Islands
- Tarsipes: Honey possum - Australia
- Thylacine: Tasmanian Tiger - Australia
- Vombatidae: Wombats - Australia