I've been slowly developing the bestiary for The Deluge project and trying to maintain consistency in terms of shape language and general morphology. It's an interesting process and I thoroughly enjoy thinking of the mechanics and the function of the forms put down.
Still early days, and I'm leaning more towards a quantity vs quality approach at this phase where I'm trying to determine some core creatures, and over time I return to them and add some additional details and come up with variations.
I find it easier to have a small library of concepts that I can return to every now and again and further develop, especially considering the daunting task of populating a whole world with believable designs.
I'm not an expert on animal anatomy (or human anatomy for that matter) but I'm slowly learning and working on things - it is a field that I find very interesting and enjoy working on.