Tarsometatarsus

Tarsometatarsus 

a bone in birds located between the ti bia and the toes. The tarsometatarsus is formed by the concrescence of the third tarsal bone with the three middle (second through fourth) metatarsal bones that are concresced lengthwise. In Archeopteryx the metatarsal bones were free. In some adult extant birds, for example, penguins and frigate birds, the tarsometatarsus has traces of concrescence—openings and little grooves between the metatarsal bones. The length of the tarsometatarsus differs in different species of birds; for example, in climbing parrots it is very short, and in marsh birds it is the same length as the long tibias. The males of some Galliformes have a spur on the dorsal side of the tarsometatarsus. The fossils of giant reptiles (predatory dinosaurs), whose legs reveal a convergent resemblance to the legs of birds, also had a tarsometatarsus similar to that of birds.