The astragalar dorsal foramen and the astragalar flexor groove in Felidae and Coypus

Abstract The dorsal foramen and the flexor groove are traditionally considered traits of plantigrade and pentadactyl mammals, and therefore basal unspecialized taxa, and they are often cited as a features that would have limited plantar flexion of the foot. Blood vessels, nerves, ligaments and tendons have been proposed passing through the foramen. During the last two years I had the opportunity to dissect three roadkills: a Myocastor coypus, a Felis catus and a Leopardus geoffroyi. I found the distinct presence of the upper joint capsule border before the end of the trochlea in the three animals. The limit of the trochlea being marked by the posterior edges of the lateral and medial malleolar facets. The astragalar foramen was present in both felids. Through the dorsal foramen was a unidentified blood vessel. No nerves or ligaments were found passing through the foramen. The flexor digitorum longus muscle of L. geoffroyi had a sesamoid at the height of the tibioastragalar articulation. Although these are considered traits of plantigrade and pentadactyl mammals, they are common in Carnivora, particularly common in felids, being observed at least in the genera Felis, Leopardus, Panthera, Prionailurus, Puma, and Smilodon.