Tarsometatarsus
Long Bone, Appendicular Skeleton
Also known as: Bird Drumstick Bone / Lower Leg Bone
Classification
Long Bone, Appendicular Skeleton
Dimensions
Generally long and slender, ranging from a few centimeters in small songbirds to over thirty centimeters in large wading birds or ostriches. It is typically the straightest bone in the bird's lower leg.
Key Features
Look for a distinct 'pulley' shape at the bottom end and a long, central shaft with deep grooves or ridges running down the length. These ridges are where tendons once sat. The bone often has a square or rectangular cross-section rather than being perfectly round, and is famously hollow and very light for its size.
Similar Bones
It is often confused with the Tibiotarsus (the bone directly above it). You can tell them apart because the tarsometatarsus is usually more angular and lacks the large, rounded 'kneecap' area found at the very top of the leg. It also looks similar to the cannon bone of a deer, but bird bones are much thinner-walled and lighter.
Across Species
The tarsometatarsus is unique to birds and some dinosaurs. While mammals have separate ankle bones (tarsals) and mid-foot bones (metatarsals), birds have these fused into a single, strong column. In swimming birds like ducks, this bone is often flattened like a paddle to reduce water resistance. In contrast, birds of prey have a thick, robust tarsometatarsus to handle the force of catching heavy meals.
Evolutionary History
This bone is a masterclass in avian efficiency. It evolved from the separate foot and ankle bones of theropod dinosaurs. Over millions of years, the fusion of these elements created a lightweight, rigid structure that allowed birds to take off with more power and land with better shock absorption. It essentially moved the 'ankle' high up the leg, allowing the bird to stand on its toes.
Photography Tips
Lay the bone against a solid, contrasting background and include a ruler for scale. Capture one shot showing the long ridges on the front and another shot focusing on the ends, particularly the 'pulley' shape at the bottom, which is a major identification marker.