Why marsupials are only found in australia?

Marsupials are primarily found in Australia due to a combination of factors, including their origins in South America, a single migration event across Antarctica to Australia, and the subsequent isolation of Australia, allowing for unique evolutionary paths.

Fossil evidence and DNA studies suggest that marsupials originated in the New World, specifically South America.

Migration Across Antarctica:

A group of ancestral marsupials migrated from South America, across Antarctica, and into Australia.

As Australia broke off from Antarctica and moved northwards, its isolation from other landmasses became complete, allowing for the independent evolution of marsupials in Australia.

In Australia, marsupials encountered a different environment with fewer competing placental mammals, allowing them to flourish and diversify.