I think that four legged creatures are a nightmare for animators. You either have to be realistic (means: study the animal in real life), or comical (means: make people laugh and be original and inventive). Both need long study and lots of practice.
A good begin seems to be to study horses, because they're big and because they've been done a lot (search YouTube for "horse animation"). Don't study anatomy, though, because you get side-tracked too much. Just use the anatomy as a reference.
Anatomy is meant as a reference anyway, and not to depict a living breathing animal. Anatomy is indeed published as a flat picture, sometime even based on carcases. You want to study moving breathing animals, and capture some of their life. Notice, for instance, that an animal never moves in a straight line, ever. You couldn't know that from an anatomy book.
Eadweard Muybridge has published a good reference book, called
Animals In Motion (Amazon link).
Too much for me, though. I'm busy studying human anatomy, from a DVD course by Riven Phoenix, "The Structure of Man - Learn To Draw The Human Figure From Your Mind". I want to have the discipline to draw a character consistently from all sides. At this moment, none of my drawings have a close resemblance, not even when I draw the same pose from the same side several times.
Edit: What the heck. I just bought the book by Muybridge online and hope to see it in the mail within 7 work days. It costed me only 33 euros incl. p&p.
