Calcaneus
Short bone, part of the appendicular skeleton
Also known as: Heel bone
Classification
Short bone, part of the appendicular skeleton
Dimensions
Varies widely by animal, ranging from a stubby cube in smaller mammals to an elongated lever in running animals like horses and deer, forming the prominent rear pillar of the foot.
Key Features
Characterized by a sturdy, blocky body with a prominent notch or hook at one end and a rough, textured surface where heavy tendons attach. It is usually one of the densest and heaviest bones in the lower limb.
Similar Bones
Can be easily confused with other large ankle or wrist bones, such as the talus. However, the heel bone is distinguished by its elongated shape and the prominent shelf or groove designed for heavy tendon pull, unlike the rounded, smooth surfaces of bones that form gliding joints.
Across Species
In digitigrade runners like cats and dogs, the heel bone is lifted high off the ground as part of a springy lower leg. In plantigrade animals like humans and bears, it rests firmly on the ground to bear the brunt of every step. In jumping specialists like rabbits and kangaroos, it is remarkably stretched out to store and release elastic energy for massive leaps.
Evolutionary History
The heel bone evolved as early tetrapods adapted to walking on land, transforming from a simple cluster of ankle bones into a dedicated lever for pushing off the ground. Over millions of years, its shape has been fine-tuned by natural selection to match everything from the digging claws of moles to the running hooves of ungulates.
Photography Tips
Place the bone on a neutral, solid-colored background with a coin or ruler for scale. Use soft, angled lighting to highlight the rough texture of the tendon attachment areas and capture multiple views, including top-down and profile angles.