i would recommend putting animals in the game where players have some flexibility in creating the exact species they want from basic models. this way, it would make things easier for you and the users. it does get a bit tiring to keep clicking through the arrows to find exactly what you want.
imo, i believe you should only include horses, lions, and wolves. this way, instead of making completely different models for deer, dogs, jaguars, antelope, whatever, you can add simpler tools like making the muzzle smaller, choosing which ears, which tail, and which markings. you could also add a few sliders for other small details, like back hunch (e.g for hyenas) or larger hind legs.
of course, there is no need to imply my idea into the game if you find modelling a bunch of different species to your liking and other players'. im going to list specie groups (i guess?) instead of what animals.
Canine model (default wolf-looking)
Feline model (default lion-looking)
Equine (default horse-looking)
Mustelid (default weasel-looking)
i am not quite sure about reptiles. if you decide to place reptiles or lizards in the game, i would give it a wide range of sizes and such since some players may want to play a crocodile.
keep in mind that finding certain horns/teeth/ect could be a little stressful for some players. i highly recommend having things such as teeth, horns, claws, and most natural things an animal can possess accessible during customization.
before anyone wants to correct me, i know equines felines and canines were confirmed, i just put them there for examples.
(hope i made sense!)