Archosauriformes (

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

for 'ruling lizards', and

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

for 'form') is a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

diapsid Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The earliest traditionally identified diapsids, the araeosc ...

reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

s encompassing

archosaurs Archosauria () or archosaurs () is a clade of diapsid sauropsid tetrapods, with birds and crocodilians being the only extant taxon, extant representatives. Although broadly classified as reptiles, which traditionally exclude birds, the cladistics ...

and some of their close relatives. It was defined by Jacques Gauthier (1994) as the clade stemming from the

last common ancestor A most recent common ancestor (MRCA), also known as a last common ancestor (LCA), is the most recent individual from which all organisms of a set are inferred to have descended. The most recent common ancestor of a higher taxon is generally assu ...

of Proterosuchidae and Archosauria. Phil Senter (2005) defined it as the most exclusive clade containing '' Proterosuchus'' and Archosauria. Gauthier as part of the ''

Phylonyms The ''International Code of Phylogenetic Nomenclature'', known as the ''PhyloCode'' for short, is a formal set of rules governing phylogenetic nomenclature. Its current version is specifically designed to regulate the naming of clades, leaving the ...

'' (2020) defined the clade as the last common ancestor of '' Gallus'', ''

Alligator An alligator, or colloquially gator, is a large reptile in the genus ''Alligator'' of the Family (biology), family Alligatoridae in the Order (biology), order Crocodilia. The two Extant taxon, extant species are the American alligator (''A. mis ...

'', and '' Proterosuchus'', and all its descendants. Archosauriforms are a branch of archosauromorphs which originated in the

Late Permian Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudonym used by Dave Groh ...

(roughly 252

million years ago Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...

) and persist to the present day as the two surviving archosaur groups:

crocodilians Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchi ...

and

birds Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

. 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 An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with Archosauriformes, archosauriforms, first appearing during the Triassic Period. Among Extant ...

(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 Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

group, and its usage as a taxonomic category has been rejected under modern

cladistic Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...

systems. The name Archosauriformes is intended as a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

replacement compatible with modern taxonomy.

Evolutionary history

Early archosauriforms, informally termed " proterosuchians", were superficially crocodile-like animals with sprawling gaits, carnivorous habits, and long hooked snouts. Unlike the bulk of their therapsid contemporaries, archosauriforms survived the catastrophic end-Permian mass extinction. The Late Permian proterosuchid '' Archosaurus'' is similar in appearance to its

Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between 251.9 Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which ...

relative, ''Proterosuchus''. Within a few million years after the beginning of the

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

, the archosauriformes had diversified past the "proterosuchian" grade. The next major archosauriform group was Erythrosuchidae, a family of

apex predator An apex predator, also known as a top predator or superpredator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the hig ...

s with massive heads, the largest terrestrial carnivorous reptiles up to that time. In 2016,

Martin Ezcurra Martin may refer to: Places Antarctica * Martin Peninsula, Marie Byrd Land * Port Martin, Adelie Land * Point Martin, South Orkney Islands Europe * Martin, Croatia, a village * Martin, Slovakia, a city * Martín del Río, Aragón, Spain * M ...

provided the name Eucrocopoda for the clade including all archosauriforms more crownward (closer to archosaurs) than erythrosuchids. He defined the clade all taxa more closely related to '' Euparkeria capensis'', '' Proterochampa barrionuevoi'', '' Doswellia kaltenbachi'', '' Parasuchus hislopi'', ''

Passer domesticus The house sparrow (''Passer domesticus'') is a bird of the sparrow family Passeridae, found in most parts of the world. It is a small bird that has a typical length of and a mass of . Females and young birds are coloured pale brown and grey, ...

'' (the house sparrow), or ''

Crocodylus niloticus The Nile crocodile (''Crocodylus niloticus'') is a large crocodilian native to freshwater habitats in Africa, where it is present in 26 countries. It is widely distributed in sub-Saharan Africa, occurring mostly in the eastern, southern, and ce ...

'' (the Nile crocodile) than to '' Proterosuchus fergusi'' or ''

Erythrosuchus africanus ''Erythrosuchus'' (from , 'red' and , 'crocodile') is an extinct genus of archosauriform reptiles from the early Triassic of South Africa. Remains have been found from the Cynognathus Assemblage Zone of the Beaufort Group in the Karoo of South ...

''. The name translates to "true crocodile feet", in reference to the possession of a crocodilian-style crurotarsal ankle. Eucrocopodans include the families Euparkeriidae (small, agile reptiles), Proterochampsidae (narrow-snouted predators endemic to

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

), and Doswelliidae (heavily armored Laurasian reptiles similar to proterochampsids), as well as various other strange reptiles such as ''

Vancleavea ''Vancleavea'' is a genus of extinct, armoured, non-archosaurian archosauriforms from the Late Triassic of western North America. The type species, type and only known species is ''V. campi'', named by Robert Long & Phillip A Murry in 1995 in pa ...

'' and '' Asperoris''. The most successful archosauriforms, and the only members to survive into the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

, were the

archosaur Archosauria () or archosaurs () is a clade of diapsid sauropsid tetrapods, with birds and crocodilians being the only extant taxon, extant representatives. Although broadly classified as reptiles, which traditionally exclude birds, the cladistics ...

s. Archosauria includes crocodilians, birds, and all descendants of their

common ancestor Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. According to modern evolutionary biology, all living beings could be descendants of a unique ancestor commonl ...

. Extinct archosaurs include

aetosaur Aetosaurs () are heavily armored reptiles belonging to the extinct order (biology), order Aetosauria (; from Ancient Greek, Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized Omnivore, omnivorous or Herbivore, herbivor ...

s, rauisuchids (both members of the crocodilian branch),

pterosaurs Pterosaurs are an extinct clade of flying reptiles in the Order (biology), order Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 million to 66 million years ago). Pterosau ...

, and non-avian

dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

(both members of the avian branch).

Metabolism

Vascular density and

osteocyte An osteocyte, an oblate-shaped type of bone cell with dendritic processes, is the most commonly found cell in mature bone. It can live as long as the organism itself. The adult human body has about 42 billion of them. Osteocytes do not divide an ...

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. 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. 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. ''

'' 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. Ornithosuchians and poposaurs are stem-crocodilians that show high growth rates similar to those of basal archosauriforms. 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. A similar process occurred in phytosaurs, which were also semi-aquatic. The similarities between

pterosaur Pterosaurs are an extinct clade of flying reptiles in the order Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 million to 66 million years ago). Pterosaurs are the earli ...

ornithischia Ornithischia () is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek ...

n and

coelurosauria Coelurosauria (; from Greek, meaning "hollow-tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyra ...

n integument suggest a common origin of

thermal insulation Thermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with s ...

(feathers) in ornithodirans at least 250 million years ago. Erythrosuchids living in high latitudes might have benefited from some sort of insulation. If ''

Longisquama ''Longisquama'' is a genus of extinct reptile. There is only one species, ''Longisquama insignis'', known from a poorly preserved skeleton and several incomplete fossil impressions from the Middle Triassic, Middle to Late Triassic Madygen Formati ...

'' was an archosauromorph, it could be associated with the origin of feathers.

Relationships

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 A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

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.

Sources

* *

References

External links

Paleos
{{Taxonbar, from=Q282487 Lopingian first appearances Extant Permian first appearances Taxa named by Jacques Gauthier Taxa described in 1986