Metapodial (Metacarpal or Metatarsal)
Long bone, part of the limb (appendicular) skeleton
Also known as: Cannon bone, shank bone, or long foot bone
Classification
Long bone, part of the limb (appendicular) skeleton
Dimensions
In many mammals, these are slender and elongated. In larger hoofed animals like deer or cattle, they can range from 8 to 15 inches in length with a straight, stout shaft and chunky, rounded ends.
Key Features
It is characterized by a very straight, long middle section (the shaft) that is often D-shaped or circular in cross-section. The bottom end usually features one or two pulley-like rollers where the toe bones attach. In many hoofed animals, a deep vertical groove runs down the front or back of the shaft.
Similar Bones
This can be confused with a Radius or Tibia. However, the metapodial is usually straighter and lacks the complex, cup-shaped 'socket' joints found at the top of the lower leg or forearm bones. Look for the distinct 'pulley' shape at the bottom end to confirm it is a foot bone.
Across Species
The appearance of this bone varies wildly by lifestyle. In humans, these are the small bones in the palm of the hand or arch of the foot. In contrast, 'running' animals like horses and deer have highly elongated metapodials that lift the heel off the ground, allowing them to run on their tiptoes for greater speed. In some species, multiple foot bones have fused together into a single, strong 'cannon bone' to support heavy weight.
Evolutionary History
This bone represents a fascinating story of terrestrial adaptation. Early land-dwelling vertebrates had five separate toes. Over millions of years, creatures adapted for speed (like prehistoric horses and hoofed mammals) lost their outer toes and saw their central foot bones lengthen and thicken to form a single, efficient pillar for high-speed locomotion.
Photography Tips
To help with identification, take one photo of the bone lying flat and another looking directly at the ends. Always include a common object like a coin, ruler, or pen for scale, as size is the best clue for determining which animal the bone came from.