This tarsal, the calcaneum, is often found as a fossil because the bone is dense and because in life there is little meat on the bone to attract carnivores. Calcanea (plural) are diagnostic -- that is, they can be identified to family or genus. In this image, the Pleistocene Equus sp. tarsal is compared to a smaller, Mio-Pliocene Neohipparion sp. calcaneum.