Metatarsal
Long bone; part of the limb (appendicular) skeleton.
Also known as: Foot bone, hindfoot bone, or shank bone
Classification
Long bone; part of the limb (appendicular) skeleton.
Dimensions
These bones are generally narrow and straight, much longer than they are wide. In many mammals, they are about the length of a human finger or palm, depending on the species.
Key Features
It has a long, straight shaft with two distinct ends. The upper end is usually flatter for meeting the ankle, while the lower end is often rounded or has a pulley-like shape to help the toes flex. The shaft itself may have a slight curve and is often somewhat square or D-shaped in a cross-section rather than perfectly round.
Similar Bones
It is often confused with its front-limb counterpart, the metacarpal (hand bone). Metatarsals are typically slightly longer and more slender than metacarpals of the same animal. It might also be mistaken for a finger or toe bone (phalanx), but a phalanx is usually much shorter and tapers more significantly toward one end.
Across Species
The appearance of this bone varies wildly across species to suit their lifestyle. In fast-running hoofed animals like deer or horses, these bones have fused and elongated into a single, sturdy 'cannon bone' that supports high-speed running. In tree-climbing primates, they remain flexible and spread apart to help with grasping branches. Whales have significantly shortened and flattened versions tucked away in their fins, while birds have a specialized fused bone called a tarsometatarsus that forms the lower part of their leg.
Evolutionary History
These bones originated from the small, many-boned feet of early land-dwelling tetrapods. Over millions of years, as different lineages moved into specialized niches, the number of these bones was often reduced. The trend in many modern mammals has been toward lengthening these bones to increase stride length, effectively allowing animals to walk or run on their toes for greater efficiency and speed.
Photography Tips
Lay the bone next to a common object like a coin or ruler for size. Take photos from the top, the side, and looking directly at both ends. Soft, natural light from the side helps reveal the subtle ridges and the specific shape of the joint surfaces, which are the most important clues for identification.