4) Animals, lacking any magickal or supernatural abilities, generally, are easy to swap for one another if needed. For example, although there are stats in the SRD for both wolves and hyeanas, couldn't you use the stats for one as a good approximation for the other? Same for leapord and cougar, bison, aurochs and yak, deer and antelope, etc. The great diversity of life in the animal kingdom isn't really going to be meaningfully represented in game stats and still offer us any difference. I might well be justified in insisting that a South American scarlet macaw and a European raven are two very different animals, but for the life of me I can't figure out why they should have different stats from each other. They're both among the most intelligent of birds, they have a tradition as serving as companions/familiars (for witches for ravens, for pirates as macaws), they both have a limited ability to mimic human speech (at least in literature, if not always reality) and they're about the same size, they have similar claws, their beaks aren't necessarily the same, but really is that going to make any different on the bite attack?
When I went to go stat out my Pleistocene subglacial megafaunal components, I found that with existing animals and a handful of dire animals, I didn't have any gaps at all, and in fact, I was a bit spoiled for choice, because books like Frostburn gave me needlessly divergent stats for a few creatures.
