Antarctica

Now, wait a minute.

If it only lived in fresh water, like lakes and rivers, how did it get from Africa to South America and, as far as we can tell, nowhere in between? Uh, and then you've got other examples like this, like there's a Triassic land-based therapsid called, uh, Sinonathus, also found in the fossil record of South America and Africa, among a few other equally baffling locations like Antarctica, huh?

Mm-hmm.

These examples showed, along with lots of other evidence that we have now, that these two land masses used to be one, that, you know, the range was one continuous range hundreds of millions of years ago, and these animals died, their remains were deposited, they were quickly buried, they became fossilized, and then the land split apart, and the Atlantic Ocean in between was formed.

But it, uh, plate tectonics also helps explain why there were such different collections of animals on Sunda and Sahul to begin with.

They were once separated by much more ocean than they are now.

Sahul, and again, this is modern-day Australia and New Guinea and some other associated islands, this was once part of the same land mass as what is now Antarctica.

And over tens of millions of years in isolation from the Afro-Eurasian and American land masses, this ancient continent experienced its own distinct branch of evolution, giving us, for example, marsupials instead of the placental mammals that you would find on the rest of the globe.