Calcaneus
Short bone, part of the limb skeleton
Also known as: Heel bone
Classification
Short bone, part of the limb skeleton
Dimensions
Varies widely by species, from a few centimeters in small mammals to over twenty centimeters in large ungulates. It forms a robust, elongated block designed to act as a powerful lever for the lower limb.
Key Features
Look for a robust, chunky block-like shape with a prominent projecting knob or hook at one end where powerful tendons attach. It features smooth articular surfaces where it links with neighboring ankle bones.
Similar Bones
Can be confused with other large tarsal or carpal bones from the foot or wrist. The heel bone is typically distinguished by its substantial length and the presence of a distinct projecting lever arm for muscle attachment.
Across Species
In digitigrade animals like dogs and cats, the heel bone is lifted high off the ground, forming the prominent back point of the hock joint. In ungulates such as deer and horses, it is heavily elongated to maximize leverage for running speed. In plantigrade animals like humans and bears, the heel rests directly on the ground to provide a stable platform for standing and walking.
Evolutionary History
The heel bone evolved as terrestrial vertebrates moved away from sprawling limb postures to upright stances. Over deep time, its shape shifted from a simple anchoring point for foot muscles into a specialized lever arm that enhances leaping and running efficiency.
Photography Tips
Place the bone on a neutral, non-glossy background with bright, even lighting to highlight the surface texture and contours. Take multiple shots: one showing the overall profile, one focusing on the articulation areas, and include a small ruler or coin for scale.