Article: Systematics and plate tectonics in the spread of marsupials

Geophysical evidence that the likely route of colonization of Australia by mammals was from South America via Antarctica is accepted. Though conclusive evidence is still lacking, the available evidence suggests that didelphoid marsupials were present in South America before placental mammals. The suggestion that marsupials dispersed to Australia before a climatic or geological change closed this route to the later-appearing placentals remains the simplest explanation of the absence of placentals from Australia.