Tarsometatarsus
Long bone, part of the appendicular skeleton adapted for weight-bearing and locomotion
Also known as: Lower leg and foot fusion bone, bird drumstick foot
Classification
Long bone, part of the appendicular skeleton adapted for weight-bearing and locomotion
Dimensions
Varies widely from a few centimeters in small songbirds to over thirty centimeters in large wading birds or flightless runners; generally slender, elongated, and reinforced with internal bracing struts.
Key Features
Look for a long, straight shaft with a cluster of distinct pulley-shaped bumps at the lower end where the toes attach, and a fused, somewhat lumpy or ridged upper end where it connects to the middle leg bone.
Similar Bones
Can be confused with the tibiotarsus (the main lower leg bone above it), but the tibiotarsus typically features a distinct hinged roller joint at the lower end rather than multiple toe-attachment pulleys. It may also resemble mammalian foot bones, but those are unfused and much shorter.
Across Species
Unlike mammals which have separate ankle and foot bones, birds fuse these elements into a single sturdy column called the tarsometatarsus. In running birds like ostriches, this bone is tremendously elongated and thick to absorb impact. In perching birds, it is shorter and lightweight, often featuring specialized pulleys at the lower end for toe tendons.
Evolutionary History
Over millions of years of dinosaur evolution, the bones of the lower foot gradually fused together to reduce weight and increase stability during bipedal movement and the takeoff phase of flight. This streamlined design minimized leg mass while maximizing leverage.
Photography Tips
Place the bone on a solid, neutral-background surface with good side lighting to highlight the surface ridges and the toe-attachment pulleys at the bottom. Include a coin or ruler for scale, and take one full-length shot from the front as well as a close-up of the bumpy end where the toes connect.