Antartican organisms (extinct)

[DrDeth]

@Blake

In the real world we have three natural experiments: Australia, South America./Antarctica and the rest of the planet. In Australia marsupials dominated and placentals became completely extinct extinct. In south America, marsupials completely dominated the carnivore/omnivore niches and placentals were restricted to herbivory. In the rest of the world placentals became completely extinct.

I think you meant to say “In the rest of the world *marsupials *became completely extinct.”

Other than that, I agree with you nearly 100%.