Avemetatarsalia in the context of "Most recent common ancestor"

Archosauria (lit. 'ruling reptiles') or archosaurs (/ˈɑːrkəˌsɔːr/) is a clade of diapsid sauropsid tetrapods, with birds and crocodilians being the only known extant representatives. Although broadly classified as reptiles, which traditionally exclude birds, the cladistic sense of the term includes all living and extinct relatives of birds and crocodilians such as non-avian dinosaurs, pterosaurs, phytosaurs, aetosaurs and rauisuchians as well as many Mesozoic marine reptiles. Modern paleontologists define Archosauria as a crown group that includes the most recent common ancestor of living birds and crocodilians, and all of its descendants.

The base of Archosauria splits into two clades: Pseudosuchia, which includes crocodilians and their extinct relatives; and Avemetatarsalia, which includes birds and their extinct relatives (such as non-avian dinosaurs and pterosaurs). Older definitions of the group Archosauria rely on shared morphological characteristics, such as an antorbital fenestra in the skull, serrated teeth, and an upright stance. Some extinct reptiles, such as proterosuchids and euparkeriids, also possessed these features yet originated prior to the split between the crocodilian and bird lineages. The older morphological definition of Archosauria nowadays roughly corresponds to Archosauriformes, a group named to encompass crown-group archosaurs and their close relatives.

Pseudosuchia (from Ancient Greek ψεύδος (pseúdos), meaning "false", and Σοῦχος (Soûkhos), meaning "Sobek") is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs", in contrast to the "bird-line archosaurs" or Avemetatarsalia. Despite Pseudosuchia meaning "false crocodiles", the name is a misnomer as true crocodilians are now defined as a subset of the group.

The clade Pseudosuchia is potentially equivalent to another term, Crurotarsi, even though the latter has a different, node-based definition: "all taxa the least inclusive clade containing Rutiodon carolinensis (Emmons, 1856), and Crocodylus niloticus (Laurenti, 1768)." Many paleontologists of the late 20th century took this proposal for granted, using Crurotarsi as the term for crocodilian ancestors. In 2011, a major revision of Triassic archosaur relations proposed that Rutiodon's group, Phytosauria, was not as closely related to other traditional "crurotarsans", at least compared to avemetatarsalians such as pterosaurs and dinosaurs. Under that interpretation, Crurotarsi would be a much broader clade than Pseudosuchia. Other recent studies continue to support a more traditional phylogeny with phytosaurs as an early branch of Pseudosuchia. If the traditional interpretation is maintained, Pseudosuchia and Crurotarsi are roughly equivalent categories.

Euparkeriidae is an extinct family of small carnivorous archosauriforms which lived from the Early Triassic to the Middle Triassic (Anisian). While most other early archosauriforms walked on four limbs, euparkeriids were probably facultative bipeds that had the ability to walk on their hind limbs at times. The most well known member of Euparkeriidae is the species Euparkeria capensis, which was named by paleontologist Robert Broom from the Karoo Basin of South Africa in 1913 and is known from several nearly complete skeletons. The family name was first proposed by German paleontologist Friedrich von Huene in 1920; Huene classified euparkeriids as members of Pseudosuchia, a traditional name for crocodilian-line archosaurs from the Triassic (Pseudosuchia means "false crocodiles"). However, phylogenetic analyses performed in the 21st century place Euparkeriidae as a group of Archosauriformes, a position outside Pseudosuchia and close to the ancestry of both crocodile-line archosaurs and bird-line archosaurs (which include dinosaurs and pterosaurs). However, they are probably not direct ancestors of archosaurs.

Several other species apart from Euparkeria have been assigned to the family, but many are dubious or have been determined to have been placed in the family incorrectly. One study has suggested that Euparkeriidae may not represent a true evolutionary grouping or clade. Instead, the family may represent an evolutionary grade of small archosauriforms (making it paraphyletic) or a group of species that each evolved small body sizes through evolutionary convergence (making it polyphyletic). However, other studies consider the family valid, albeit difficult to diagnose. Euparkeriidae is defined as the most inclusive clade containing Euparkeria capensis but not Crocodylus niloticus (the nile crocodile) or Passer domesticus (the house sparrow).

Archosauria or archosaurs (/ˈɑːrkəˌsɔːr/) is a clade of diapsid sauropsid tetrapods, with birds and crocodilians being the only known extant representatives. Although broadly classified as reptiles, which traditionally exclude birds, the cladistic sense of the term includes all living and extinct relatives of birds and crocodilians such as non-avian dinosaurs, pterosaurs, phytosaurs, aetosaurs and rauisuchians as well as many Mesozoic marine reptiles. Modern paleontologists define Archosauria as a crown group that includes the most recent common ancestor of living birds and crocodilians, and all of its descendants.

The base of Archosauria splits into two clades: Pseudosuchia, which includes crocodilians and their extinct relatives; and Avemetatarsalia, which includes birds and their extinct relatives (such as non-avian dinosaurs and pterosaurs). Older definitions of the group Archosauria rely on shared morphological characteristics, such as an antorbital fenestra in the skull, serrated teeth, and an upright stance. Some extinct reptiles, such as proterosuchids and euparkeriids, also possessed these features yet originated prior to the split between the crocodilian and bird lineages. The older morphological definition of Archosauria nowadays roughly corresponds to Archosauriformes, a group named to encompass crown-group archosaurs and their close relatives.

Postosuchus, meaning "Crocodile from Post", is an extinct genus of rauisuchid reptiles comprising two species, P. kirkpatricki and P. alisonae, that lived in what is now North America during the Late Triassic. Postosuchus is a member of the clade Pseudosuchia, the lineage of archosaurs that includes modern crocodilians (the other main group of archosaurs is Avemetatarsalia, the lineage that includes all archosaurs more closely related to birds than to crocodilians). Its name refers to Post Quarry, a place in Texas where many fossils of the type species, P. kirkpatricki, were found.

It was one of the apex predators of its area during the Triassic, larger than the small dinosaur predators of its time (such as Coelophysis). It was a hunter that probably preyed on large, bulky herbivores such as dicynodonts and many other creatures smaller than itself (such as early dinosaurs). The skeleton of Postosuchus is large and robust, with a deep skull and a long tail. It was a large animal, up to 5–6 m (16–20 ft) long or even more. The extreme shortness of the fore limbs relative to the hind limbs, the very small fore paws, and measurements of the vertebrae suggest that Postosuchus may have been committed to bipedal locomotion.

Aphanosauria ("hidden lizards") is an extinct group of reptiles distantly related to dinosaurs (including birds). They are at the base of a group known as Avemetatarsalia, one of two main branches of archosaurs. The other main branch, Pseudosuchia, includes modern crocodilians. Aphanosaurs possessed features from both groups, indicating that they are the oldest and most primitive known clade of avemetatarsalians, at least in terms of their position on the archosaur family tree. Other avemetatarsalians include the flying pterosaurs, small bipedal lagerpetids, herbivorous silesaurids, and the incredibly diverse dinosaurs, which survive to the present day in the form of birds. Aphanosauria is formally defined as the most inclusive clade containing Teleocrater rhadinus and Yarasuchus deccanensis but not Passer domesticus (house sparrow) or Crocodylus niloticus (Nile crocodile). This group was first recognized during the description of Teleocrater.

Although only known by a few genera, Aphanosaurs had a widespread distribution across Pangaea in the Middle Triassic. They were fairly slow quadrupedal long-necked carnivores, a biology more similar to basal archosaurs than to advanced avemetatarsalians such as pterosaurs, lagerpetids, and early dinosaurs. In addition, they seemingly possess 'crocodile-normal' ankles (with a crurotarsal joint), showing that 'advanced mesotarsal' ankles (the form acquired by many dinosaurs, pterosaurs, lagerpetids, and advanced silesaurids) were not basal to the whole clade of Avemetatarsalia. Nevertheless, they possessed elevated growth rates compared to their contemporaries, indicating that they grew quickly, more like birds than other modern reptiles. Despite superficially resembling lizards, the closest modern relatives of aphanosaurs are birds.