>>51344461>>51344475obviously there would need to be new mons added. The fossil record in real life is far from complete so encountering new mons in the past makes logical sense. Also you could include mons that evolve via ancient power, like swinub and yanma, and add new evos for existing mons that evolve while in the past into prehistoric forms as a kind of regional evolution type of thing.
There is plenty to work with.