Those ecosystems exist, they just had issues with reproduction, predators, possibly disease. We can control for them middle one a bit. Apparently there were so

Those ecosystems exist, they just had issues with reproduction, predators, possibly disease. We can control for them middle one a bit. Apparently there were some pretty exotic animals that Aboriginal cultures and Neandrathals wiped out, because of the low frequency of them. Didn't take too much effort on our part. In the same way that Wolves or Bisons can be re-introduced in some areas, probably some extinct animals can as well with a little bit of help.