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Archosaurs made more rapid progress towards erect limbs than synapsids, and this gave them greater stamina by avoiding Carrier's constraint. An objection to this explanation is that archosaurs became dominant while they still had sprawling or semi-erect limbs, similar to those of Lystrosaurus and other synapsids. [citation needed]
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 .
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.
Figure 1:In mammals, the quadrate and articular bones are small and part of the middle ear; the lower jaw consists only of dentary bone.. While living mammal species can be identified by the presence of milk-producing mammary glands in the females, other features are required when classifying fossils, because mammary glands and other soft-tissue features are not visible in fossils.
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 phalangeal count for archosaurs is 2-3-4-5-3; many archosaur lineages have a reduced number of digits, but have the same phalangeal formula in the digits that remain. In other words, paleontologists assert that archosaurs of different lineages tend to lose the same digits when digit loss occurs, from the outside to the inside.
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The archosaurs became the dominant group during the Triassic period, developing into the well-known dinosaurs and pterosaurs, as well as the pseudosuchians. The Mesozoic is often called the "Age of Reptiles", a phrase coined by the early 19th-century paleontologist Gideon Mantell who recognized the dinosaurs and the ancestors of the ...