The possible causes of the extinction of Australia's megafauna have been intensely debated in recent times. One aspect of this debate that requires greater understanding is the ecological role that the megafauna played in the environment, and how the mammal community was altered following the extinctions. This proposal addresses this issue using new, innovative methods for assessing diet and community structure published by my collaborators and me this year in Nature. This established the relationship between complexity of mammal teeth and the diet of the species. We will detect how mammalian community structure has changed in Australia over the last one hundred thousand years to address the possible causes of extinction.