Giraffes and camels have long legs, relatively short bodies, and large feet.
A common explanation for their unusual gaits is that the gait prevents fore and hind feet from getting in each other’s way.
If you refer to feet by their initials, LF for left fore, RH for right hind, and so on, you can write down the walking pat terns of particular animals. When most mammals walk, they move their feet in turn, always in the same order, at more or less equal intervals of time:
and so on. The asterisks indicate the time intervals, *’ for long and * for short.
In trotting, which is a faster gait, the legs move two at a time, in diagonally opposite pairs:
(LF + RH)*”**(RF + LH)*’ (LF + RH)*’ (RF + LH)
and so on.
Camels, however, do something different. Instead of trotting, they pace, moving the two feet on the same side of the body together:
(LH + LF)’ ” (RH + RF)****(LH + LF)****(RH + RF)
and so on.
Some believe that walking giraffes move the two feet of the same side of the body at once, like the camel, but that isn’t quite true. Films analyzed by the American zoologist Milton Hildebrand showed that walking giraffes move their feet like this:
LF* RH*RF ‘ LH” LF ‘RH*RF ‘LH
and so on.
Long and short time intervals alternate and the forelegs move slightly after the hind legs of the same side.
In trotting, a foreleg swings back while the hind leg on the same side swings forward, so there is a danger of the feet colliding, if the legs are long. In a pacing walk, the legs on one side of the body both swing forward, then both swing back, so the fore and hind feet are kept well out of each other’s way.
The fact that some long-legged breeds of dog also pace instead of trotting supports this explanation of the giraffe’s pacing walk.
In horses, there is less danger of fore–hind collisions in the standard walk than in the trot. The giraffe’s pace-like walk reduces the danger further.
This may explain the giraffe’s unusual gait. But I feel bound to point out that both camels and giraffes gallop successfully. In galloping, both forelegs swing back while both hind legs are swinging forward, offering plenty of scope for collisions.
Hildebrand recorded giraffe-like walking gaits for the cheetah, a hyena, and the gerenuk, a long-legged antelope.
No experiments seem to have been done to find out whether there is any difference in energy costs between trotting and pacing, or between the horse’s and the giraffe’s styles of walking, but we would expect any differences to be small.