Tarsometatarsus
Long bone, part of the appendicular skeleton
Also known as: Bird lower leg bone, fusion of ankle and foot bones
Classification
Long bone, part of the appendicular skeleton
Dimensions
Varies widely from under an inch in tiny songbirds to over a foot in large ratites like ostriches, characterized by a slender, rigid shaft connecting widened joint surfaces at both ends.
Key Features
Look for a remarkably slender, hollow, and straight tubular shaft with distinct pulley-shaped grooves at the lower end for toe attachment and a flat, triangular plate at the upper end where it meets the main lower leg bone.
Similar Bones
Can be easily confused with the tibiotarsus (the main lower leg bone of birds) or mammalian fibulas; however, the tarsometatarsus is distinguished by its unique triangular upper platform and the multiple pulley grooves at the lower tips for the toes.
Across Species
Unlike mammals which keep their ankle and foot bones separate, birds fuse these elements into a single, highly specialized bone that adds an extra segment to the leg length, effectively giving birds a higher spring and longer stride for takeoff and landing.
Evolutionary History
This fused structure evolved from the separate ankle and foot bones of theropod dinosaurs, streamlining the avian leg to reduce weight at the extremities and improve aerodynamic efficiency during flight.
Photography Tips
Place the bone on a neutral, non-reflective background with a coin or ruler for scale, and take shots from both a flat overhead view to show the entire length and a close-up profile of the lower end to capture the toe joints clearly.