This is a biodiversity suggestion-have animals living on islands exhibit insular dwarfism (the phenomenon where animals living on island end up evolving to be much smaller than their counterparts on the mainland) and island gigantism. As an example of the former, there is rather famously the real-life "hobbit" H. Florensis (still controversy over whether it is a separate species), the key deer, the (extinct) honshu wolf, and various examples which arose in recent geologic history such as pygmy mammoths, elephants, mastodons, and other normally large creatures. On the other end of the scale, you get gigantism resulting in creatures like the giant moas, RL giant eagles (Hast's Eagle grew to a size, and especially weight, to where it could hunt the moa), the komodo dragon, elephant bird (also extinct-many of these species were the first to be wiped out when humans found their islands, sadly), galapagos tortises, and many more. It would be interesting to see this in-game as well.
Edit: Ass an addendum, I would also like to see scavengers-vultures, jackals, hyenas, etc-feed on carcasses that get left sitting around-many predators also scavenge when possible, so pretty much every predator in game would also be able to do this. Would give one hell of an incentive to make a proper graveyard/crypt asap, instead of letting the dwarf bones just sit there until it's convenient. Admittedly, this practice may be part of the reason i tend to get tantrum spirals...