Metatherian fossils have been found throughout the world, but only remained diverse in South America and Australia until recently. Once the isthmus of Panamá formed and the Great American Biotic Interchange occurred, much of what had been a diverse marsupial metatherian assemblage - including hypercarnivores such as borhyaenids - in South America was replaced by placentals. Australia remained relatively isolated from eutherians, and this is why marsupials dominate the fauna today

Though Eutherians have caused the extinction of at least one notable marsupial - the Thylacine - in modern times and restricted the range of several others to Tasmania also.