Proterosuchidae is an early, possibly paraphyletic, assemblage of basalarchosauriformes whose fossils are known from the Latest Permian of Russia and the Early Triassic of southern Africa, Russia, China, Australia, and Antarctica. The name comes from Greek πρότερο- ("first") and σοῦχος ("crocodile"). They were slender, medium-sized (about 1.5 meters long), long-snouted and superficially crocodile-like animals, although they lack the armoured scutes of true crocodiles, and in their skeletal features are much more primitive. Their most characteristic feature is a distinct down-turning of the premaxilla (the front of the upper jaw, which overhangs the lower jaw). The limbs are short and indicate a sprawling posture, like contemporary lizards but unlike most later archosaurs.
Some studies consider Proterosuchidae to be a paraphyletic grouping, meaning that it does not form a true clade with a single common ancestor and proterosuchids as its only descendants. Instead, they are a chain of successively basal archosauriforms. Below is a cladogram from Ezcurra et al. (2010):
^Ezcurra, M.D.; Lecuona, A.; Martinelli, A. (2010). "A new basal archosauriform diapsid from the Lower Triassic of Argentina". Journal of Vertebrate Paleontology. 30 (5): 1433–1450. doi:10.1080/02724634.2010.501446.