Marsupials and other metatherians apparently arrived in South America before the beginning of the Paleogene, at the end of the Cretaceous.
South American didelphoids radiated widely as carnivores and omnivores and some species in the past reached the size of a panther, e.g. The marsupial populations in Asia and North America went extinct, possibly as a result of competition with placental mammals among other factors, and the populations on southern continents remained in those safe havens. We have some specimens of the family Didelphidae. Scientifically known as Didelphis virginiana, the Virginia opossum is the only marsupial found in North America. THE NEW WORLD MARSUPIALS There are some 250 species of living marsupials in the world and more than 150 fossil species are known. During this period of migration the North American marsupials became extinct, followed by extinctions in Europe during the Miocene epoch of the Tertiary period. We have some specimens of the family Didelphidae. This is a list of the native wild mammal species recorded in South America.South America's terrestrial mammals fall into three distinct groups: "old-timers", African immigrants and recent North American immigrants.
The marsupials of South America did survive, however, and they are still there today. The differences between this carnivorous marsupial and the saber-toothed tigers, however, were significant.
Marsupials were excluded in turn from large herbivore niches in South America by the presence of native placental ungulates (now extinct) and xenarthrans (whose largest forms are also extinct). Marsupials colonized first South America, and from there moved on to Antarctica and then Australia. The earliest relatives of Australian marsupials, the Microbiotheria, appear in the earliest assemblage. The carnivorous sparassodonts evolved the largest metatherian predators known, such as the 600 kg Subcategories. With time, it turned out, among other things, that the latter is much better adapted to ecosystem changes than its rival from South America. This category has the following 4 subcategories, out of 4 total.
The marsupials and xenarthrans are "old-timers", their ancestors having been present on the continent since at least the very early Cenozoic Era. AMERICAN MARSUPIALS SUPER COHORT MARSUPIALIA COHORT AMERIDELPHIA. They have shorter gestation periods due to their yolk-type placenta compared to the placental mammals who experience longer gestation periods. The American marsupials are now assigned to two families, the Didelphidae (the opossums), Order Didelphimorphia, which occur in both North and South America,and the Caenolestidae (the shrew opossums), Order Paucituberculata, found only in South America.
It could be said that Thylacosmilus was South American smilodon.
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