Marsupials

Scientific name: Marsupialia

Picture of red kangaroos, a species of marsupial.
Marsupials are a group of mammals give that have a marsupium, a pouch in which their young develop. Photo © J und C Sohns / Getty Images.

Marsupials (Marsupialia) are a group of mammals that like most other groups of mammals bear live young when the embryos are in an early stage of development. In some species such as the bandicoot, the gestation period is as short as 12 days. The young crawl up the mother's body and into the her marsupium—a pouch located on the mother's abdomen. Once inside the marsupium, the baby attaches to a nipple and nurses on milk until it is large enough to leave the pouch and better fend for itself in the outside world.

Larger marsupials tend to give birth to a single offspring at a time, while smaller sized marsupials give birth to larger litters.

Marsupials were common in many areas of North America during the Mesozoic and outnumbered placental mammals. Today, the only living marsupial in North America is the opossum.

Marsupials first appear in the fossil record from South America during the Late Paleocene. They later appear in the fossil record from Australia during the Oligocene, where they underwent diversification during the Early Miocene. It was during the Pliocene that the first of the larger marsupials appeared. Today, marsupials remain one of the dominant land mammals in South America and Australia. In Australia, a lack of competition has meant that marsupials were able to diversify and specialize. Today there are insectivorous marsupials, carnivorous marsupials, and herbivorous marsupials in Australia.

Most South American marsupials are small and arboreal animals.

The reproductive tract of female marsupials differs from placental mammals. In female marsupials there are two vaginas and two uteruses whereas placental mammals have a single uterus and vagina. Male marsupials also differ from their placental mammal counterparts.

They have forked penis. The brains of marsupial are also unique, it is smaller than that of placental mammals and lacks a corpus callosum, the nerve tract that connects the two cerebral hemispheres.

Marsupials are quite varied in their appearance. Many species have long back legs and feet and an elongated face. The smallest marsupial is the long-tailed planigale and the largest is the red kangaroo. There are 292 species of marsupials alive today.

Classification

Marsupials are classified within the following taxonomic hierarchy:

Animals > Chordates > Vertebrates > Tetrapods > Amniotes > Mammals > Marsupials

Marsupials are divided into the following taxonomic groups:

  • American marsupials (Ameridelphia) - There are about 100 species of American marsupials alive today. Members of the group include opossums and shrew opossums. American marsupials are the older of the two lineages of modern marsupials, which means it was members of this group that later migrated to Australia and diversified.
  • Australian marsupials (Australidelphia) - There are about 200 species of Australian marsupials alive today. Members of this group include the Tasmanian devil, numbats, bandicoots, wombats, marsupial moles, pygmy possums, koalas, kangaroos, wallabies and many others. Australian marsupials are further divided into five groups.
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    Klappenbach, Laura. "Marsupials." ThoughtCo, Aug. 9, 2016, thoughtco.com/marsupials-profile-130402. Klappenbach, Laura. (2016, August 9). Marsupials. Retrieved from https://www.thoughtco.com/marsupials-profile-130402 Klappenbach, Laura. "Marsupials." ThoughtCo. https://www.thoughtco.com/marsupials-profile-130402 (accessed January 18, 2018).