It has been my understanding the developers haven't introduced stronger animals due to problems with the current AI and the ease of trapping animals.
So my suggestion is to have random den/burrow spawns in the wilderness. The player(s) would right click the burrow to enter it. once inside, the player(s) would not be able build any objects, so they would have to fight the animal(s) legit.
Once the animal is dead, upon map unload, that particular den/burrow would disappear, you could have a couple per super grid active at any time (each a different animal strength maybe).
To find the den/burrow, you would either come upon it randomly or find an animal footprint which would spawn like a herb. You would track the footprint like a scent to the den/borrow. the scent would only be good for that particular den/burrow and would disappear when that particular animal was killed or if you tracked it to many times.
This would introduce players to tracking without needing to be around people, and promote group combat if the animals were made strong enough.