Quadrupedal animals have multiple gaits; at higher speeds, they'll start bringing the forelegs down together at closer points in time.

Check out, for instance, this video of an actual cheetah running around: http://www.youtube.com/watch?v=KIeXEiJuJUY - you can see the front paws coming down very close to each other in time and space, followed by the wide-spread rear paws making huge leaps forwards.

Also a quick images search for "horse muybridge" may be enlightening - Muybridge's books are super well-known in the animation circles I come from, as they were the first major works of research into high-speed photography documenting How Stuff Moves. You can see that horses have a whole bunch of different gaits available to them; most other animals are similar, but less tractable to a photographer's whims!