Mule deer (Odocoileus hemionus) are ungulates – mammals with hooves. Their hooves are made of keratin, a type of solidified hair, and are comparable to a human fingernails.
The ancient ancestors of deer had five toes or fingers. Over time the “thumb” or great toe was lost completely. The digits analogous to the human index finger and “pinky” moved toward the rear of the foot and became vestigial bone splints known as dewclaws, while the remaining two toenails lengthened, hardened and evolved into a cloven (split) hoof. Dewclaws do not touch the ground. Meanwhile the metacarpal and metatarsal bones (equivalent to our arch and palm bones) fused to form the long cannon bone or lower leg bone.
The hoof grows throughout the mule deer’s life and is worn down by rocks or hard soil. Without constant abrasion, such as in soft soil or in captivity, the hoof of a mule deer will grow long and even deform.
The mule deer’s two toes are pointed, with the outside one usually slightly (1/4″) longer than the inner one. When sprinting the pointed toes can dig in powerfully to provide traction. The outer rim of each hoof is much harder than the central portion. During most of the year the inner surface is spongy and almost convex, however this area retracts somewhat in the winter giving the hoof a concave appearance. The hard edges of the hoof are good for rough terrain, but do not provide traction on smooth surfaces such as ice. The entire mule deer hoof and the dewclaws splay out on soft ground, increasing the weight-bearing surface and providing support.
Although the the mule deer’s foot with its small, cloven hooves appears delicate, it is well adapted for the deer’s habitat and fleeing from predators. Only on ice or other smooth surfaces does the mule deer hoof prove deficient.
I found and photographed this fresh mule deer leg while hiking along Ash Creek (Lassen County CA).