Final answer:
The discovery of fossils of similar marsupials across different continents supports the theory of plate tectonics.
Step-by-step explanation:
The theory supported by this discovery is the theory of plate tectonics. Plate tectonics explains how Earth's surface is made up of several large plates that are constantly moving. The discovery of fossils of similar marsupials across different continents suggests that these continents were once connected and have since drifted apart due to the movement of tectonic plates.
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