Placental mammals vs Marsupials
The South Americanmarsupials flourished greatly while they had the continent to themselves since the southern supercontinent was fragmenting and drifting apart and South America was moving slowly northwards. In due course, it connected with North America by way of a land bridge in the neighbourhood of Panama. Down this corridor came the placentalmammals to dispute the possession of South America with the marsupial residents. In the course of this rivalry, most species of marsupials disappeared, leaving only the tough, opportunistic opossums. One of these has even invaded North America, the land from where the placental invaders had come from. That marsupial invader is the Virginiaopossum.