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Metatheria:
Marsupials are the first of the two great groups of therian (live-bearing) mammals, distinguished by their tendency to expel the embryo from the womb at a very early stage, and then nurse the infant externally while it develops. Marsupials originated in the early Cretaceous, possibly in North America , and then spread around the globe. Today, marsupials are most numerous in Australia , where almost every mammal belong to that order. They also exist in great numbers in South America and some dwell in Eurasia and North America.
Many New World marsupials belong to the large and varied family Didelphidae, which on Home-Earth is represented by opossums. These marsupials are distinguished by the fact that they give partial birth to an embryo from one womb into another, where it develops for a time before graduating to a pouch. Didelphids are very similar to the marsupial precursors, and most have retained the ancient habits of the arboreal insectivore.
Stimpies and teddies are placid, heavily-built arboreal metatherians somewhat related to the didelphids. They evolved in South America, and the vegetarian, koala-like stimpies are found only in that continent's jungles, but the more omnivorous teddies extend far into North America.
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