Archosauriformes (Greek for 'ruling lizards', and 'form') are a clade of diapsid reptiles that developed from Archosauromorph ancestors some time in the Late Permian (roughly 250 million years ago). 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 long, with a sprawling elbows-out stance and long snouts. Unlike the bulk of their therapsid contemporaries, the Proterosuchids happily survived the catastrophe at the end of the Permian, perhaps because they were opportunistic scavengers, perhaps 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), who in turn were the ancestors of the small agile Euparkeriidae, from whom a number of successfully more advanced families - the Archosaurs proper - evolved rapidly to fill empty ecological niches in the devastated global system.

Pre-Euparkeria Archosauriformes were in the past included in the suborder Proterosuchia of the order Thecodontia. Under the cladistic methodology, the Proterosuchia are rejected as a paraphyletic assemblage, and the pre-Archosaurian taxa are simply considered as basal Archosauriformes.



  • Gauthier, J. A. 1986. "Saurischian monophyly and the origin of birds". Memoirs of the California Academy of Science 8:1–55
  • Gauthier, J. A., Kluge A. G. , and Rowe, T. (1988) "Amniote phylogeny and the importance of fossils". Cladistics 4:105–209

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