Archosauriforms Temporal range:Latest Permian–Present,252–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Row 1 (basal archosauriforms):Erythrosuchus africanus,Euparkeria capensis; Row 2 (Pseudosuchia):Crocodylus mindorensis,Typothorax coccinarum; Row 3 (Avemetatarsalia):Casuarius casuarius,Anhanguera piscator.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauromorpha
Clade:	Crocopoda
Clade:	Archosauriformes Gauthier, 1986
Subgroups[2]
†Antarctanax †Barberenasuchus †Collilongus †Crosbysaurus? †Cuyosuchus †Eorasaurus †Fenhosuchus †Kalisuchus †Sarmatosuchus †Sphodrosaurus †Syntomiprosopus †Uatchitodon †Vigilosaurus †Vjushkovisaurus †Vonhuenia †Wangisuchus †Proterosuchidae †Erythrosuchidae †Protopyknosia EucrocopodaEzcurra, 2016 †Asperoris †Dorosuchus †Heteropelta †Litorosuchus †Marcianosuchus †Polymorphodon †Vancleavea †Euparkeriidae[1] †Proterochampsia Crurotarsi †Phytosauria Archosauria

Archosauriformes (Greek for 'ruling lizards', andLatin for 'form') is aclade ofdiapsidreptiles encompassingarchosaurs and some of their close relatives. It was defined byJacques Gauthier (1994) as the clade stemming from thelast common ancestor ofProterosuchidae and Archosauria.^[3]Phil Senter (2005) defined it as the most exclusive clade containingProterosuchus and Archosauria.^[4] Gauthier as part of thePhylonyms (2020) defined the clade as the last common ancestor ofGallus,Alligator, andProterosuchus, and all its descendants.^[5] Archosauriforms are a branch ofarchosauromorphs which originated in theLate Permian (roughly 252million years ago) and persist to the present day as the two surviving archosaur groups:crocodilians andbirds.

Archosauriforms present several traits historically ascribed to the group Archosauria. These include serrated teeth set in deep sockets, a more active metabolism, and anantorbital fenestra (a hole in the skull in front of the eyes). Reptiles with these traits have also been termed "thecodonts" in older methods of classification. Thecodontia is aparaphyletic group, and its usage as ataxonomic category has been rejected under moderncladistic systems. The name Archosauriformes is intended as amonophyletic replacement compatible with modern taxonomy.

Early archosauriforms, informally termed "proterosuchians", were superficially crocodile-like animals with sprawling gaits, carnivorous habits, and long hooked snouts. Unlike the bulk of theirtherapsid contemporaries, archosauriforms survived the catastrophicend-Permian mass extinction. The Late Permian proterosuchidArchosaurus is similar in appearance to itsEarly Triassic relative,Proterosuchus. Within a few million years after the beginning of theTriassic, the archosauriformes had diversified past the "proterosuchian"grade. The next major archosauriform group wasErythrosuchidae, a family ofapex predators with massive heads, the largest carnivorous reptiles up to that time.

In 2016,Martin Ezcurra provided the nameEucrocopoda for the clade including all archosauriforms morecrownward (closer to archosaurs) than erythrosuchids. He defined the clade all taxa more closely related toEuparkeria capensis,Proterochampa barrionuevoi,Doswellia kaltenbachi,Parasuchus hislopi,Passer domesticus (the house sparrow), orCrocodylus niloticus (the Nile crocodile) than toProterosuchus fergusi orErythrosuchus africanus. The name translates to "true crocodile feet", in reference to the possession of a crocodilian-stylecrurotarsal ankle.^[2] Eucrocopodans include the familiesEuparkeriidae (small, agile reptiles),Proterochampsidae (narrow-snouted predators endemic toSouth America), andDoswelliidae (heavily armoredLaurasian reptiles similar to proterochampsids), as well as various other strange reptiles such asVancleavea andAsperoris.

The most successful archosauriforms, and the only members to survive into theJurassic, were thearchosaurs. Archosauria includes crocodilians, birds, and all descendants of theircommon ancestor. Extinct archosaurs includeaetosaurs,rauisuchids (both members of the crocodilian branch),pterosaurs, and non-aviandinosaurs (both members of the avian branch).^[6]

Vascular density andosteocyte density, shape and area have been used to estimate the bone growth rate of archosaurs, leading to the conclusion that this rate had a tendency to grow in ornithodirans and decrease in pseudosuchians.^[7] The same method also supports the existence of high resting metabolical rates similar to those of living endotherms (mammals and birds) in theProlacerta-Archosauriformes clade that were retained by most subgroups, though decreased inProterosuchus,Phytosauria and Crocodilia.^[8] Erythrosuchids andEuparkeria are basal archosauriforms showing signs of high growth rates and elevated metabolism, withErythrosuchus possessing a rate similar of the fastest-growing dinosaurs. Sexual maturity in those Triassic taxa was probably reached quickly, providing advantage in a habitat with unpredictable variation from heavy rainfall to drought and high mortality.Vancleavea andEuparkeria, which show slower growth rates compared toErythrosuchus, lived after the climatic stabilization. Early crown archosaurs possessed increased growth rates, which were retained by ornithodirans.^[9]Ornithosuchians andpoposaurs are stem-crocodilians that show high growth rates similar to those of basal archosauriforms.^[10]

Developmental, physiological, anatomical and palaeontological lines of evidence indicate that crocodilians evolved from endothermic ancestors. Living crocodilians are ambush predators adapted to a semi-aquatic lifestyle that benefits from ectothermy due to the lower oxygen intake that allows longer diving time. The mixing of oxygenated and deoxygenated blood in their circulatory system is apparently an innovation that benefits ectothermic life. Earlier archosaurs likely lacked those adaptations and instead had completely separated blood as birds and mammals do.^[11][12] A similar process occurred in phytosaurs, which were also semi-aquatic.^[13]

The similarities betweenpterosaur,ornithischian andcoelurosaurian integument suggest a common origin ofthermal insulation (feathers) in ornithodirans at least 250 million years ago.^[14][15] Erythrosuchids living in high latitudes might have benefited from some sort of insulation.^[13] IfLongisquama was an archosauromorph, it could be associated with the origin of feathers.^[16][13]

Below is a cladogram from Nesbitt (2011):^[17]

Below is a cladogram from Senguptaet al. (2017),^[18] based on an updated version of Ezcurra (2016)^[2] 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.^[2]

• Gauthier, J. A. (1986)."Saurischian monophyly and the origin of birds". In Padian, K. (ed.).The Origin of Birds and the Evolution of Flight. Memoirs of the California Academy of Sciences. Vol. 8.California Academy of Sciences. pp. 1–55.ISBN 978-0-940228-14-6.
• Gauthier, J. A.; Kluge, A. G.; Rowe, T. (June 1988)."Amniote phylogeny and the importance of fossils"(PDF).Cladistics.4 (2).John Wiley & Sons:105–209.doi:10.1111/j.1096-0031.1988.tb00514.x.hdl:2027.42/73857.PMID 34949076.S2CID 83502693.

• Paleos
• Mikko's Phylogeny Archive

• Archosauriformes
• Lopingian first appearances
• Extant Permian first appearances
• Taxa named by Jacques Gauthier
• Taxa described in 1986

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• Short description matches Wikidata
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