Archosauriformes

Archosauriformes (Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles that developed from archosauromorph ancestors some time in the Late Permian (roughly 250 million years ago). It was defined by Jacques Gauthier (1994) as the clade stemming from the last common ancestor of Proterosuchidae and Archosauria (the group that contains crocodiles, pterosaurs, dinosaurs, and birds); Phil Senter (2005) defined it as the most exclusive clade containing Proterosuchus and Archosauria. These reptiles, which include members of the family Proterosuchidae and more advanced forms, were originally superficially crocodile-like predatory semi-aquatic animals about 1.5 meters (5 ft) long, with a sprawling elbows-out stance and long snouts. Unlike the bulk of their therapsid contemporaries, the proterosuchids survived the catastrophe at the end of the Permian, perhaps because they were opportunistic scavengers or because they could retreat into water to find respite from an overheated climate. Any such scenarios are hypothetical; what is clearer is that these animals were highly successful in their new environment, and evolved quickly. Within a few million years at the opening of the Triassic, the proterosuchids had given rise to the Erythrosuchidae (the first sauropsids to totally dominate their environment), which in turn were the ancestors of the small agile Euparkeriidae, from which a number of successfully more advanced families – the archosaurs proper – evolved rapidly to fill empty ecological niches in the devastated global system. The Archosauria includes crocodylians, birds, and their extinct relatives. The archosaurs were the only members of the Archosauriformes which survived the late Triassic extinction. Pre-Euparkeria Archosauriformes have previously been included in the suborder Proterosuchia of the order Thecodontia. Under the cladistic methodology, Proterosuchia has been rejected as a paraphyletic assemblage, and the pre-archosaurian taxa are simply considered as basal Archosauriformes. Below is a cladogram from Nesbitt (2011): Below is a cladogram from Sengupta et al. (2017), based on an updated version of Ezcurra (2016) that reexamined all historical members of the 'Proterosuchia' (a polyphyletic historical group including proterosuchids and erythrosuchids). 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 are nomina dubia are indicated by the note 'dubium'. Bold terminal taxa are collapsed.