Animators often need to bring animals to life in animation. The anatomy of most four-legged animals, as well as birds, reptiles, and dinosaurs, is quite different from our primate podiatry. This article covers the basics of animating four-legged mammals.
Biology of a Four-Legged Mammal
The skeleton of four-legged mammal is similar to the skeleton of a human: Both have four limbs, and those limbs contain the same bones. The differences lie in the lengths and arrangements of the bones.
Consider a dog, for example. Although humans walk on their heels and toes, the dog walks only on its toes. As Figure 1 shows, the dog's "heel" is far above the ground, approximately where our knee would be. The dog's knee is actually even higher up, as are its thighs and hips. The front legs are similar to our arms, but, again, the dog walks on its fingers. Like the heel, the dog's "wrist" is far above the ground, with the elbow even higher.
Figure 1 A dog walks on bones that are our toes and fingers, with the wrist and ankle above the ground.
Heavy-set animals, such as the hippo, tend to have short, stubby legs. This is because the animal's skin tends to hang lower, obscuring the upper part of the leg. A skeleton for a hippo, for example, looks much like the skeleton for any other four-legged creature, except that the upper parts of the legs are hidden inside the body (see Figure 2).
Figure 2 On a hippo, the elbows and knees are located near the belly, with the upper parts of the leg hidden under the heavy skin.