Marsupials, such as kangaroos and koalas, did not originate in Australia. According to biologist Robin Beck, their ancestors existed for at least 70 million years before arriving on the continent's lands. The earliest marsupials lived in North America, where they evolved during the Cretaceous period, splitting from placental mammals at least 125 million years ago.
These animals thrived on the supercontinent Laurasia and migrated to present-day South America about 66 million years ago, when the dinosaurs went extinct. There, the diversity of marsupials grew, and they occupied niches previously characteristic of placental mammals. Although many species have gone extinct, South America is still home to more than 100 species of opossums.
About 40–35 million years ago, a land bridge in Antarctica allowed marsupials to migrate from South America to Australia. Fossil findings on Seymour Island confirm this movement.
