Minecraft wiki entry for Development_versions, associated text: Added following block tags to decide the corresponding creatures to spawn:
animals_spawnable_on
Contains Grass Block.
axolotls_spawnable_on
Contains Clay.
foxes_spawnable_on
Contains Grass Block, Snow, Snow Block, Podzol, and Coarse Dirt.
goats_spawnable_on
Contains Stone, Snow, Powder Snow, Snow Block, Packed Ice, and Gravel.
mooshrooms_spawnable_on
Contains Mycelium.
parrots_spawnable_on
Contains Grass Block, Air, #leaves, and #logs.
polar_bears_spawnable_on_in_frozen_ocean
Contains Ice.
rabbits_spawnable_on
Contains Grass Block, Snow, Snow Block, and Sand.
wolves_spawnable_on
Contains Grass Block, Snow, and Snow Block.