Archosauriformes

Archosauriforms Temporal range: 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 †Vjushkovisaurus †Vonhuenia †Wangisuchus †Proterosuchidae †Erythrosuchidae †Protopyknosia Eucrocopoda Ezcurra, 2016 †Asperoris †Dorosuchus †Heteropelta †Polymorphodon †Euparkeriidae[1] †Proterochampsia Crurotarsi † Phytosauria Archosauria

Archosauriformes (

Archosauriforms present several traits historically ascribed to the group Archosauria. These include serrated teeth set in deep sockets, a more active metabolism, and an antorbital 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 a paraphyletic group, and its usage as a taxonomic category has been rejected under modern cladistic systems. The name Archosauriformes is intended as a monophyletic replacement compatible with modern taxonomy.

Evolutionary history

Early archosauriforms, informally termed "

Vascular density and osteocyte 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.^[6] The same method also supports the existence of high resting metabolical rates similar to those of living endotherms (mammals and birds) in the Prolacerta-Archosauriformes clade that were retained by most subgroups, though decreased in Proterosuchus, Phytosauria and Crocodilia.^[7] Erythrosuchids and Euparkeria are basal archosauriforms showing signs of high growth rates and elevated metabolism, with Erythrosuchus 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 and Euparkeria, which show slower growth rates compared to Erythrosuchus, lived after the climatic stabilization. Early crown archosaurs possessed increased growth rates, which were retained by ornithodirans.^[8] Ornithosuchians and poposaurs are stem-crocodilians that show high growth rates similar to those of basal archosauriforms.^[9]

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.^[10][11] A similar process occurred in phytosaurs, which were also semi-aquatic.^[12]

The similarities between pterosaur, ornithischian and coelurosaurian integument suggest a common origin of thermal insulation (feathers) in ornithodirans at least 250 million years ago.^[13][14] Erythrosuchids living in high latitudes might have benefited from some sort of insulation.^[12] If Longisquama was an archosauromorph, it could be associated with the origin of feathers.^[15][12]

Relationships

Below is a cladogram from Nesbitt (2011):^[16]

Below is a cladogram from Sengupta et al. (2017),

Crocopoda

Allokotosauria Rhynchosauria Boreopricea funerea Prolacertidae SAM-PK-591 " Ankistrodon indicus " (dubium) " Blomosuchus georgii " (dubium) Tasmaniosaurus triassicus  Archosauriformes  Chasmatosuchus magnus Chasmatosuchus rossicus Gamosaurus lozovskii Chasmatosuchus vjushkovi Vonhuenia friedrichi Proterosuchidae Eorasaurus olsoni Kalisuchus rewanensis Fugusuchus hejiapanensis Sarmatosuchus otschevi Cuyosuchus huenei Erythrosuchidae  Eucrocopoda  Asperoris mnyama Dorosuchus neoetus Euparkeria capensis  Proterochampsia  Doswelliidae Proterochampsidae   Archosauria    Pseudosuchia  Phytosauria The rest of Pseudosuchia  Avemetatarsalia  Aphanosauria Ornithodira

Sources

• ISBN 978-0-940228-14-6
  .
• S2CID 83502693
  .