Evolution of toes in Equidae

The illustrations show the digits, metatarsals (foot bones), and wrist bones of various species of Equids, drawn to the same scale. Hyracotherium is a 4-toed digitrade ungulate, meaning that it runs with the digits in contact with the ground and the foot bones raised, similar to the gait of a modern cat or dog. Weight passes through the third (middle) toe, an arrangement called mesaxonic. In succesive species, the lateral digits are further reduced and the metatarsals become fused. In modern Equus, the fused cannon bone supports a single toe.