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Marsupials |
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A254 Marsupials
Marsupials are a clade of mammals characterized by a distinctive pouch
(called the marsupium) in which females carry their young through early
infancy. Females have two vaginas, which lead to separate uteruses, but both
open externally through the same orifice. A third canal, the median vagina, is
used for birth. Marsupials do not have a placenta, so babies not much larger
than an embryo crawl from their mother’s median vagina to her pouch where
they feed from her nipples.
There are 334 species. Around 200 are native to Australia and neighboring
northern islands. They include the most well known, such as the kangaroos
and the koala. The 100 or so New World species are generally small animals.
There is only one marsupial native to North America, the Virginia Opossum.
No one knows how it got here.
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