"Animating animals is usually fun, but can often be complicated and technical. Figuring out what to do with all those legs can really trip up an animator. We can animate human–shaped characters a lot easier than multi–legged beasts because we have an intuitive knowledge of the way bipeds move.
It is easy for an animator to act out a motion when the character moves like us; feeling the action 'in the body' helps us understand how to animate it. So what happens when the character is a quadruped and you don't have that intuitive feel at your disposal? How do you make that movement believable? Suitable reference and a sophisticated media player is the place to start.
Luckily for the animation community, there is a wealth of reference material that can help. I'll walk you through my process for animating quadruped locomotion and share classic references that will help you deconstruct the fundamentals of the four gaits: walk, run, trot and gallop. I'll also share an example of my own 3D walk animation and offer technical tips for creating believable quadruped locomotion cycles."
(Cathy Feraday Miller, Gamasutra)
Fig.1 Richard Williams, uploaded by "animan1999" on 25 Aug 2009, YouTube.
Fig.2 Richard Williams, uploaded by "animan1999" on 1 Sep 2009, YouTube.