I'd like to introduce you to a world where humans never have existed. This world is totally populated by anthromorphic animals. Anthros can be any animal you want. You can have the anthros living like humans do or as animals. BUT ALL ANTHROS MUST BE NAKED BECAUSE CLOTHES WERE NEVER CREATED!
Now for chapters you can have magic of any kind or super science. You can have anthro animals becoming feral animals through magic or science or just casting magic.
You can have them have sex or giving birth.
You can have them voring each other if you like.
Now I hope you have fun with this story.