The conclusion that is best supported by the discovery of a fossil leaf from a tropical plant in Antarctica is: The land that is currently near the South Pole was once located closer to the equator.
This conclusion is supported by the understanding of plate tectonics and the historical climate changes on Earth. Fossil evidence of tropical plants in currently cold regions suggests that those regions had a different climate in the past, indicating that they were once situated in a warmer, more tropical part of the Earth.