Tossing one of these up, whenever I gotta draw a new animal or some fantasy critter based in reality I always start by studying the skull. It's a lot of fun, and lets me see how far I can push certain features for expression without losing that animal's distinguishing qualities.
Try comparing the skulls of two related animals like Lions and Panthers, it's neat!
Link
Bluegrass
Awesome sketches, I love seeing creature studies! Remember cattle don't have any front teeth on the top jaw! c: