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Archosaurs are a subgroup of archosauriforms, which themselves are a subgroup of archosauromorphs. Both the oldest archosauromorph (Protorosaurus speneri) and the oldest archosauriform (Archosaurus rossicus) lived in the late Permian. The oldest true archosaurs appeared during the Olenekian stage (247–251 Ma) of the Early Triassic.
The "classic" definition of archosaur utilized prior to the widespread use of cladistics is now roughly equivalent to the clade Archosauriformes. [5] Archosaurus is still considered the oldest undisputed archosauriform, as well as one of the few valid members of the family Proterosuchidae. [6]
Extinct archosaurs include non-avian dinosaurs, pterosaurs, and extinct relatives of crocodilians. 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 name Pseudosuchia was originally given to a group of superficially crocodile-like prehistoric reptiles from the Triassic period, but fell out of use in the late 20th century, especially after the name Crurotarsi was established in 1990 to label the clade (evolutionary grouping) of archosaurs encompassing most reptiles previously identified as pseudosuchians.
Archosauriformes (Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles encompassing archosaurs and some of their close relatives. It was defined by Jacques Gauthier (1994) as the clade stemming from the last common ancestor of Proterosuchidae and Archosauria. [3]
Traditionally, the order Thecodontia Owen, 1859 was divided into four suborders, the Proterosuchia (early primitive forms, another paraphyletic assemblage), Phytosauria (large crocodile-like semi-aquatic animals), the Aetosauria (armoured herbivores), and the Pseudosuchia, a wastebasket taxon intended to be paraphyletic to all later archosaurs (see e.g., Alfred Sherwood Romer's Vertebrate ...
The redefinition to cover the last common ancestor of archosaurs and lepidosaurs was the result of papers by Jacques A. Gauthier and colleagues in the 1980s. [ 6 ] Genomic studies [ 7 ] [ 8 ] [ 9 ] and comprehensive studies in the fossil record [ 10 ] suggest that turtles are closely related to archosaurs as part of Sauria, and not to the non ...
An equivalent term for the crocodilian side of the archosaur family tree is Pseudosuchia. This traditional definition of Crurotarsi assumed that phytosaurs were crown-group archosaurs and more closely related to crocodilians than to birds. However, a 2011 study argued that the phytosaur lineage evolved prior to the split between birds and ...