Editing Archosaur (section)

==Distinguishing characteristics==
Archosaurs can traditionally be distinguished from other tetrapods on the basis of several [[Synapomorphy|synapomorphies]], or shared characteristics, which were present in their [[Most recent common ancestor|last common ancestor]]. Many of these characteristics appeared prior to the origin of the clade Archosauria, as they were present in [[Archosauriformes|archosauriforms]] such as ''[[Proterosuchus]]'' and ''[[Euparkeria]]'', which were outside the [[crown group]].<ref name="NSJ11" />

[[File:Skull triapsida 1.svg|thumb|General pattern of skull fenestration in archosaurs]]

The most obvious features include teeth set in deep sockets, [[antorbital fenestra|antorbital]] and [[:File:Massospondylus Skull Steveoc 86.png|mandibular fenestrae]] (openings in front of the eyes and in the jaw, respectively),<ref name="Dyk, Kai 2011">{{cite book|title=Living Dinosaurs: The Evolutionary History of Modern Birds|url=https://archive.org/details/livingdinosaurse00dyke|url-access=limited|year=2011|publisher=John Wiley & Sons|isbn=978-0-470-65666-2|pages=[https://archive.org/details/livingdinosaurse00dyke/page/n28 10]|editor1=Gareth Dyke |editor2=Gary Kaiser }}</ref> and a pronounced [[fourth trochanter]] (a prominent ridge on the [[femur]]).<ref name="khanna2004">{{cite book|last=Khanna|first=D.R.|title=Biology Of Reptiles|year=2004|publisher=Discovery Publishing House|isbn=978-81-7141-907-4|pages=78ff}}</ref> Being set in sockets, the teeth were less likely to be torn loose during feeding. This feature is responsible for the name "[[Thecodontia|thecodont]]" (meaning "socket teeth"),<ref name="WhiKazAOver" /> which early paleontologists applied to many Triassic archosaurs.<ref name="khanna2004" /> Additionally, non-muscular cheek and lip tissue appear in various forms throughout the clade, with all living archosaurs lacking non-muscular lips, unlike most [[Non-avian dinosaur|non-avian]] [[Saurischia|saurischian]] dinosaurs.<ref>{{cite book|last=Paul|first=Gregory S.|title=The Princeton Field Guide to Dinosaurs|publisher=Princeton University Press|year=2016|isbn=978-0-691-16766-4|edition=2nd|location=Princeton, New Jersey|page=26}}</ref> Some archosaurs, such as birds, are secondarily toothless. Antorbital fenestrae reduced the weight of the skull, which was relatively large in early archosaurs, rather like that of modern [[crocodilian]]s. Mandibular fenestrae may also have reduced the weight of the jaw in some forms. The fourth trochanter provides a large site for the attachment of muscles on the femur. Stronger muscles allowed for erect gaits in early archosaurs, and may also be connected with the ability of the archosaurs or their immediate ancestors to survive the catastrophic [[Permian-Triassic extinction event]].{{Citation needed|date=April 2017}}

Unlike their close living relatives, the lepidosaurs, archosaurs lost the [[vomeronasal organ]].<ref>Poncelet, G., and Shimeld, S. M. (2020). The evolutionary origin of the vertebrate olfactory system. Open Biol. 10:200330. doi: 10.1098/rsob.200330</ref>