In Australia, marsupials and placental mammals have evolved to share many similar characteristics. This type of evolution is referred to as convergent evolution.
Convergent evolution is the independent evolution of similar features in species of different lineages. For example, a number of marsupials, each different from the other evolved from an ancestral stock, but all within the Australian island continent. Also, marsupials in Australia resemble placental mammals in the rest of the world, they evolved in isolation after Australia separated from other continents.