Proterosuchus fergusi from the Early Triassic of South Africa
They were slender, medium-sized (about 1.5 m (4 ft 11 in) long, largest specimens reached 3.5–4 m (11–13 ft)[2]), long-snouted and superficially crocodile-like animals, although they lacked the armouredscutes of true crocodiles, and their skeletal features are much more primitive. The limbs are short and indicate a sprawling posture, like contemporarylizards but unlike most later archosaurs.
Their most characteristic feature is a distinct down-turning of thepremaxilla (the front of the upper jaw, which overhangs the lower jaw).
The terminalPermian catastrophe, which killed off 95% of all types of life, cleared the world of all largetherapsids and allowed the proterosuchids to become the top predators. Within the space of five million years the proterosuchids had evolved to fill a wide variety of terrestrial and semi-aquatic niches.[3] The proterosuchids represent perhaps the earliestadaptive radiation of the archosaurs. They gave rise to theErythrosuchidae some time in the Early Triassic.[citation needed]
Recent studies consider Proterosuchidae to be at least a partiallyparaphyletic grouping, meaning that it does not form a trueclade with a single common ancestor and proterosuchids as its only descendants. Instead, they are a chain of successively basal archosauriforms.[4][5] Proterosuchidaesensu stricto is defined as "all taxa more closely related toProterosuchus fergusi than toErythrosuchus africanus,Crocodylus niloticus (theNile crocodile), orPasser domesticus (thehouse sparrow).[5] Below is a cladogram from Ezcurra (2016), that reexamined all historical members of the "Proterosuchia" (apolyphyletic historical group includingproterosuchids anderythrosuchids). The placement of fragmentary taxa that had to be removed to increase tree resolution are indicated by dashed lines (in the most derived position that they can be confidently assigned to). Taxa that arenomina dubia are indicated by the note "dubium". Bold terminal taxa are collapsed. Ezcurra (2016) recovered a monophyletic Proterosuchidae containing onlyArchosaurus and the species ofProterosuchus, however some species (e.g.Chasmatosuchus spp,Vonhuenia friedrichi) are too fragmentary to resolve whether they also fall into Proterosuchidae.Tasmaniosaurus,Fugusuchus,Sarmatosuchus,Cuyosuchus and the "Long Reef proterosuchid" (SAM P41754) on the other hand were recovered confidently outside of Proterosuchidae.[5]
^abcdEzcurra, M.D. (2016). The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms.PeerJ, e1778[1]
