There is no debate as contentious as the post-Flood boundary issue within creation science. Given that testing theories is as important as developing them, this paper offers a method to test the placement of a post-Flood boundary at different points in the stratigraphic record. Marsupial fossil presence in strata below and above a suggested post-Flood boundary can be used to calculate the likelihood of those genera being found on a single continent (notably Australia or South America) both before and after the Flood. These calculations suggest that post-Flood boundary placements in the Cenozoic, within the continents noted, face a difficult challenge. Other fossil groups with high continental endemism may be similarly useful in this type of calculation. This paper's results have implications for post-Flood biogeographic modeling.