How can evolutionary theory explain why Australia is home to relatively few native placental mammals?

Evolutionary theory explains that Australia's unique geography and long-term isolation from other continents led to a distinct evolutionary path for its fauna. The continent's separation allowed for the dominance of marsupials, which adapted to various ecological niches. Additionally, the lack of competition from placental mammals, which thrive in other regions, may have contributed to the limited diversity of native placental mammals in Australia. This evolutionary process highlights how environmental factors and historical contingencies shape species distribution.