What are marsupial? Do all of them have pouches - and while we are on that subject - why are pouches needed? All you need to know about the fascinating group of animals known as marsupials
What are marsupials?
Marsupials are pouched mammals and are a group of mammals that most of us probably associate with Australasia and Wallacea, thanks to well- known species such as kangaroos, koalas, Tasmanian devils, wombats and the now-extinct thylacine, also known as the Tasmanian tiger. In total the group has over 300 species
What is the point of a marsupial's pouch?
Marsupial newborns (called joeys) are altricious -- they're underdeveloped, equivalent to an 8-10 week-old human embryo, and gestation lasts weeks (12.5 days in some bandicoots).
Most embryonic development occurs ex utero - out of the uterus. After birth, the baby - basically a foetus - must climb multiple times its own length to reach the pouch and drink milk from a teat. Produced by a female's mammary glands during lactation, milk contains nutrients and substances that boost infant immunity - in marsupials, that mixture of molecules will change to meet their needs at different stages.
Do all marsupials have pouches?
A marsupial’s pouch is surely its most obvious distinguishing feature. And yet only slightly more than half of them possess one. In the vast majority of species, they are found only in females, who famously use them to nurture and transport their young, which are born at a very early and helpless stage of development.
In only one species of living marsupial do the males have one too. The South American water opossum (Chironectes minimus) is the world’s only semi-aquatic marsupial. While females use their pouch in the conventional way, in males it has more to do with making babies than nurturing them.
A male opossum tucks his testicles into his pouch before entering the water. It’s not known whether this is for protection, streamlining or both. Males of the extinct thylacine, or marsupial tiger, once native to Australia and New Guinea, possessed a similar organ, thought to have protected their genitals from snagging on undergrowth.
Are marsupials only found in Australasia?
However, although roughly 70 per cent of extant marsupial species are found there, there are marsupials in the Americas too. The most famous of the American marsupials is the Virginia opossum, North America’s only marsupial species, which spread northwards from South America in the Great American Interchange. ‘Opossum’ is derived from the Algonquian word ‘wapathemwa’, meaning ‘white animal’.
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What is the smallest and biggest marsupial?
Both the biggest and smallest living marsupial inhabit Australia's arid interior. The smallest marsupial is one of the secretive, carnivorous, mouse-like planigales - probably the long-tailed planigale, which lives in dry grasslands in the north. Weighing about 5g, it has a flattened skull that allows it to hunt and shelter in the deep cracks that form in sun-baked soil.
At the other end of the spectrum is the red kangaroo, males of which can weigh up to 90kg and stand nearly 2m tall. It’s not the largest marsupial ever to have lived, though.
That would be a three-tonne wombat-like animal called Diprotodon. Like many other large marsupials, Diprotodon disappeared around 40,000 years ago, and debate continues as to whether their extinction was the result of climatic changes, hunting by the first human settlers, or a combination of the two.
Answered by Stuart Blackman.
