Ornithosuchidae is an extinct family of pseudosuchian archosaurs (distant relatives of modern crocodilians) from the Triassic period. Ornithosuchids were quadrupedal and facultatively bipedal (e.g. like chimpanzees), meaning that they had the ability to walk on two legs for short periods of time. They had distinctive, downturned snouts, unique, "crocodile-reversed" ankle bones, and several other features that distinguish them from other archosaurs. Ornithosuchids were geographically widespread during the Carnian and Norian stages of the Late Triassic with members known from Argentina, Brazil, and the United Kingdom. Four genera, comprising Ornithosuchus, Venaticosuchus, Dynamosuchus, and Riojasuchus are presently known. The family was first erected by German paleontologist Friedrich von Huene in 1908. Description Skull Ornithosuchids can be identified by the presence of an arched diastema, a gap between the teeth at the front of the snout. When the jaw is closed, two large curved dentary (lower jaw) teeth fit into the diastema, which is positioned between the premaxilla and maxilla. There are two shallow depressions on the wall of the diastema to accommodate these teeth. The large dentary teeth of Ornithosuchus and Riojasuchus are placed behind a smaller procumbent dentary tooth that sticks out from the jaw. This type of tooth position is not seen in any other basal archosaurs. Another characteristic feature of ornithosuchids is their unusual downturned, overhanging snout, seen in Riojasuchus and Venaticosuchus, but not Ornithosuchus. Several other features distinguish ornithosuchids from all other early archosaurs. Ornithosuchus and Riojasuchus both possess a small fenestra, or hole, between the palatine and pterygoid bones of the palate, i.e. the roof of the mouth. The contact between the nasal and prefrontal bones of the skull is small or absent, excluded by a large contact between the frontals and lacrimals. In other archosaurs, including rauisuchians, aetosaurs, pterosaurs, and dinosauromorphs, the nasal-prefrontal contact separates the frontal from the lacrimal. Postcranial skeleton The postcranial skeleton is nearly completely known in Riojasuchus, incomplete in Ornithosuchus, and entirely unknown in Venaticosuchus. As a result, it is uncertain whether all of the postcranial traits seemingly unique to ornithosuchids actually occurred in all members of the family. Ornithosuchids known from decent postcranial remains typically had about 9 cervical (neck), 14-15 dorsal (back), 3 sacral (hip), and over 20 caudal (tail) vertebrae. Above each vertebra was a pair of bony scutes known as osteoderms. The femur (thigh bone) has a pronounced anterior trochanter. The anterior trochanter, sometimes known as the "lesser