Metatarsal
Long bone; part of the appendicular skeleton (lower limb/hind limb)
Also known as: Hind-foot bone, shank bone, or cannon bone (in ungulates)
Classification
Long bone; part of the appendicular skeleton (lower limb/hind limb)
Dimensions
In mammals, these are typically slender and cylindrical. In specialized runners like deer or sheep, they are very elongated, often making up a significant portion of the leg's overall length.
Key Features
Look for a long, straight shaft that is somewhat flattened on one side and rounded on the other. The most identifying feature is the lower end, which often has a pulley-like shape with smooth, rounded surfaces where it would meet the toe bones. The texture of the shaft is usually very dense and smooth, designed to handle the vertical weight of the animal.
Similar Bones
It is most frequently confused with the metacarpal (the corresponding bone in the front limb). Generally, metatarsals have a more square or blocky cross-section compared to the more rounded or D-shaped cross-section of front-limb metacarpals. It may also be confused with a tibia (shin bone), but the tibia is typically much thicker and has a distinct triangular top.
Across Species
The metatarsal shows incredible variety across nature. In humans, we have five short metatarsals that form the arch of the foot. In contrast, grazing animals like deer and cattle have 'cannon bones' where several of these have merged into a single, light, and very strong column. This adaptation lifts the heel high off the ground, allowing the animal to run effectively on their toes. Whales, having lost their hind limbs, possess only tiny, non-functional remnants of these bones tucked away in their body walls.
Evolutionary History
The metatarsal evolved from the simple bony rays found in the fins of lobe-finned fish. As vertebrates moved onto land, these rays became sturdier to support weight. Over millions of years, the trend in many lineages—especially fast-moving mammals—has been toward the reduction in the number of these bones and an increase in their length to provide greater leverage for sprinting away from predators.
Photography Tips
To help with identification, take photos from multiple angles: one straight on to show the full length, one from the side to show the curve, and a 'top-down' view of the joint ends. Always include a steady ruler or a common object for scale, as the size is a major clue for determining which species the bone belonged to.