Ahhhh, probably not. If, for example, you navigate to Marsupial at Wikipedia and click on the wonderful (it really really is!) DyMaxion map at the bottom of the info panel, you wiil see that a large part of South America, Central and North America also have these animals.
FWIW, the USA does indeed have Uranium deposits although I'm not sure about Central and South America.
Quoting from Wikipedia:
A 2010 analysis of retroposon insertion sites in the nuclear DNA of a variety of marsupials has confirmed all living marsupials have South American ancestors.
South America was connected to Antarctica for a long time (but not to North America), as was Australia.