Tarsometatarsus
Long Bone; appendicular skeleton (limb)
Also known as: Bird Shank, Lower Leg Bone, Drumstick base
Classification
Long Bone; appendicular skeleton (limb)
Dimensions
Generally slender and elongated, though bird-dependent. It can range from short and stout in flightless birds to remarkably thin and long in wading birds like herons.
Key Features
Look for a long, straight shaft with a complex 'pulley' shape at the bottom end where the toes attach. The top end usually has two deep pits for the upper leg to sit in. One side of the shaft often features a long groove, and in some male birds like roosters, a bony spur may project from the side.
Similar Bones
It is most often confused with the Tibiotarsus (the 'drumstick'). To tell them apart, check the bottom end: the Tarsometatarsus has distinct pulley-like bumps for three or four toes, whereas the Tibiotarsus has a simpler double-rounded joint at the bottom.
Across Species
This unique structure is a signature of bird anatomy. While mammals have separate ankle bones (tarsals) and mid-foot bones (metatarsals), birds have these fused into a single, sturdy column. In chickens or turkeys, this is the scaly part of the leg below the feathered drumstick. In water birds, it is often flattened to help with swimming, while in raptors, it is thickened to support the power of the talons.
Evolutionary History
Tracing back to theropod dinosaurs, this bone represents a shift toward a more efficient, upright, and digitigrade (toe-walking) stance. Over millions of years, the small individual bones of the ankle and foot fused together to create a rigid lever, which provided birds with more spring for takeoff and a lightweight structure for flight.
Photography Tips
Lay the bone flat on a plain background with a coin or ruler next to it for size. Take photos from the top, the side, and a close-up of the pulley-like joints at the bottom end. Soft, natural light helps show the subtle grooves on the shaft.