Yes, but please keep in mind that this will be a kid's book. If we avoid the binomial nomenclature for species and stick with common names, children will be able to associate the letter with the animal more easily.
That said, we can still be creative! For example, if you want me to paint a polar bear, you could pledge for the letter B and then specify which kind. Or if B is already taken, you could pledge the P for polar bear. Either route gets us a common name for the animal and something kids can enjoy, while also allowing you to commission me to paint the animal you want to see.