Sense the rules of this universe are similar to the ones in ours, so I assume that those animals evolved, but Raava and Vaatu are still around, Badger moles, Dragons and Sky bison might have been different, like sky bison were just bison until either Raava, Vaatu or the lion turtles gave them bending, and we see that some animals are highly intelligent, so they probably gave the three most intelligent creatures and the ones closer to there bending, I can go into more depth if you want, do you want me too?