Answer:
The Continental drift theory
Step-by-step explanation:
The Marsupials are the mammals that are mostly found in Australia and America and are characterized by the presence of a pouch that is attached to their body.
These mammals evolved from the reptiles and present abundantly in the Cenozoic era, after the extinction of dinosaurs. But they first appeared during the time of existence of dinosaurs. The continents of Australia and America eventually got separated before the naturally occurring placental mammals could evolve. This suggested a piece of evidence for the continental drift theory.
This theory describes that the continents float across the large oceans from one place to another with respect to the fixed poles.