Despite this relationship to crocodiles, Ornithosuchus was able to walk on its hind legs, like many dinosaurs. However, it probably spent most of its time on all fours, only moving bipedally when it needed to run rapidly. Its skull also resembled those of theropod dinosaurs, but more primitive features included the presence of five toes on each foot and a double row of armoured plates along the animal's back. Ornithosuchus was around 4 metres (13 ft) in length.
A single species of Ornithosuchus is recognized, O. longidens. The type species, O. woodwardi, is considered a junior synonym. O. longidens was originally named as "Dasygnathus" longidens, but the genus name Dasygnathus had already been used for a coleopteran insect, so despite being named later, the name Ornithosuchus remained in use for the genus. Ornithosuchus is the type genus of the Ornithosuchidae, a family of facultatively biped carnivores that were geographically widespread during the Late Triassic. Two other genera are currently known, Venaticosuchus and Riojasuchus.