@KoiwiGal - The thing is, one of the reasons the animals in Europe changed is because of the arrival of people. I think since people lived in Africa without changing the current fauna for a long time (before guns were introduced) that it's possible that the animals you see in Africa today are the same kind that were there twenty thousand years ago.
Evolution doesn't often work so fast as to bring up thousands of diverse species in such a short time. And the range of species available to see at this park probably wouldn't have just appeared in such a short time.
Granted, there might have been more animals back then, perhaps some which are extinct now. The lion is a good example, as it was probably living there once, but no longer is.