Why is the organic world of South America considered original?

South America for quite a long time was remote from the rest of the land, which led to the development of flora and fauna in limited conditions. The animals were forced to adapt to the hot and very humid climate of the continent. It is these two factors that make the organic world of South America unique. For example, apart from Australia, only here marsupials have survived, as well as unique amphibians and reptiles that have long disappeared from other continents, unable to withstand competition.