I sell my big animals and replace them with baby animals so I have things to evolve.
for example, trying for station dalmation I am getting hottweiler and volcamels. So I sell my level 10 volcamel and replace it with a level one. Feed it to level 3 and evolve it. Then I sell it again and replace it if I get another one. Endless things to evolve and I don't lose out on any animals that way or need too many more habitats.