Metatarsal
Long bone; part of the limb (appendicular) skeleton
Also known as: Lower leg bone, hind shank bone, or cannon bone (in hooved animals)
Classification
Long bone; part of the limb (appendicular) skeleton
Dimensions
In many mammals, this bone is significantly elongated and slender. In hooved animals, it can be quite long, often representing a substantial portion of the lower leg's total height.
Key Features
This specimen is a long, straight shaft that often features a deep groove running down the front or back. One end usually flares out into rounded, spool-like surfaces that look like the bottom of a pulley. These rounded knobs allow for a wide range of hinging movement where the bone meets the toes.
Similar Bones
It is often confused with the metacarpal (front leg/hand bone). The easiest way to tell them apart is that the metatarsal typically has a more squared or rectangular cross-section in the shaft compared to the more rounded or D-shaped shaft of the front leg version. It might also be confused with a radius, but the pulley-like joints at the bottom are the best indicator of a foot-related bone.
Across Species
The appearance of this bone varies wildly across species. In deer and cattle, multiple bones have fused over time into a single robust 'cannon bone' to provide strength for running. In contrast, birds have a unique structure where these fuse with ankle bones to form the tarsometatarsus. In plantigrade animals like bears or humans, these bones remain shorter and more spread out to support the flat of the foot.
Evolutionary History
This bone shares a common ancestry with the foot bones of early four-legged land vertebrates. Over millions of years, as diverse lineages adapted to different environments, these bones evolved. For cursorial animals—those specialized for high-speed running—natural selection favored the lengthening and fusing of these bones to create a longer lever for more efficient movement.
Photography Tips
To get the best identification image, lay the bone on a flat, neutral-colored surface. Take one shot looking straight down at the long shaft and another focusing specifically on the rounded joints at the bottom. Including a common object like a coin or a ruler in the frame helps others understand the true size of your find.