Arctic:
1. Polar bear
2. Arctic wolf
3. Reindeer (shared habitat species - arctic hare)
4. Dall sheep (shared habitat species - arctic hare)
5. Musk ox (shared habitat species - arctic hare)
6. Arctic fox
7. Wolverine
8. Moose
9. Arctic hare (shared habitat species - musk ox, dall sheep, reindeer)
10. ?
11. ?
12. ?
I feel like 12 is too many slots for the arctic with the game's current limitations. If aquatic animals could be included, you could include the walrus, ringed seal, and harp seal to fill the remaining 3 slots.
South America:
1. Llama (walkthough, shared habitat species - patagonian hare, pudu)
2. Giant anteater (walkthrough, shared habitat species, capuchin monkey, cotton headed tamarin, baird's tapir, capybara, giant armadillo, sloth)
3. Jaguar
4. Capuchin monkey (walkthrough, shared habitat species - cotton headed tamarin, giant anteater, baird's tapir, capybara, giant armadillo, sloth)
5. Ocelot
6. Maned wolf
7. Capybara (walkthrough, shared habitat species - giant anteater, capuchin monkey, cotton headed tamarin, baird's tapir, giant armadillo, sloth)
8. Sloth (any species is fine with me) (shared habitat species - giant armadillo, giant anteater, capuchin monkey, cotton headed tamarin, baird's tapir, capybara)
9. Giant armadillo (walkthrough, shared habitat species - capuchin monkey, giant anteater, baird's tapir, capybara, cotton headed tamarin)
10. Pudu (shared habitat species - llama)
11. Patagonian hare (walkthrough, shared habitat species - llama)
12. Cotton headed tamarin (walkthrough, shared habitat species - capuchin monkey, giant anteater, baird's tapir, capybara, giant armadillo, sloth)
Australia:
1. Red kangaroo (shared habitat species - koala)
2. Koala (walkthrough, shared habitat species - emu, wombat, wallaby, grey kangaroo, red kangaroo)
3. Cassowary
4. Dingo
5. Emu (walkthrough, shared habitat species - wallaby, grey kangaroo, koala, wombat)
6. Tasmanian devil
7. * Platypus (though not sure if this animal can be realistically done without diving animations. If impossible, I choose the Perentie for this slot)
8. Wallaby (any species is fine for me) (walkthrough, shared habitat species - emu, grey kangaroo, wombat, koala)
9. Wombat (walkthrough, shared habitat species - koala, grey kangaroo, emu, wallaby)
10. Grey kangaroo (walkthrough, shared habitat species - emu, wallaby, wombat, koala)
11. Thorny devil (E)
12. Red bellied black snake (E)