Archosauromorpha

Archosauromorpha is a major clade of diapsid reptiles defined as all species more closely related to archosaurs than to lepidosaurs. In cladistic usage, it includes the crown group Archosauria (crocodilians, birds, and extinct archosaurs) and a broad array of stem archosauromorphs that lie outside Archosauria but within Archosauromorpha. The group forms one of the two primary divisions of Neodiapsida, the other being Lepidosauromorpha.

The earliest archosauromorphs appear in the Late Permian, and after the Permian–Triassic extinction they diversified markedly during the Triassic. This radiation produced a wide range of forms, including early long-necked and small-bodied lineages, and ultimately led to the emergence of archosaurs, from which crocodilians, birds, and numerous extinct groups arose. The diversity of archosauromorphs reflects a broad ecological breadth, with species adapting to terrestrial, amphibious, and occasionally more specialized lifestyles.

Anatomically, archosauromorphs span a wide spectrum of morphologies, and there is no single synapomorphy that unites all members of the clade. The crown group Archosauria is characterized by features that facilitated erect or semi-erect locomotion and various skull and dental adaptations, but stem archosauromorphs predate many of these specializations. In modern phylogenetic classifications, Archosauromorpha is a well-supported clade within Diapsida; older literature sometimes treated related groups such as Prolacertiformes as paraphyletic or separate.