These include laminae on the vertebrae, a posterodorsal process of the premaxilla, a lack of notochordal canals, and the loss of the entepicondylar foramen of the humerus.

Jacques Gauthier reused the term Archosauromorpha for the archosaur lineage at the 1982 annual meeting of the American Society of Zoologists, and later used it within his 1984 Ph.D.

[5][4][6] Michel Laurin (1991) defined Archosauromorpha as a node-based clade containing the most recent common ancestor of Prolacerta, Trilophosaurus, Hyperodapedon and all of its descendants.

[8] Gauthier, as an author for Phylonyms (2020), redefined Archosauromorpha as a node-based clade containing Gallus, Alligator, Mesosuchus, Trilophosaurus, Prolacerta, and Protorosaurus.

This study found that Azendohsauridae, Triassic reptiles previously mistaken for "prosauropod" dinosaurs, were in fact close relatives of Trilophosaurus and the rest of Trilophosauridae.

A landmark 1998 study by David Dilkes completely deconstructed the concept of Prolacertiformes as a traditional monophyletic group (i.e. one whose members have a single common ancestor).

[8] Likewise, Pamelaria is now considered an allokotosaur, Macrocnemus is a tanystropheid, and Protorosaurus may be too basal ("primitive") to form a clade with any of its supposed close relatives.

[6][1] The chameleon- or tamandua-like drepanosaurs are also semi-regularly placed within Archosauromorpha,[8] although some studies have considered them to be part of a much more basal lineage of reptiles.

Genetic studies have found evidence that modern testudines (turtles and tortoises) are more closely related to crocodilians than to lizards.

Since Pantestudines may encompass the entire aquatic reptile order Sauropterygia, this means that Archosauromorpha (as Archelosauria) may be a much wider group than commonly believed.

Several recent studies place sauropterygians within Archosauromorpha group, forming a large clade including Ichthyosauromorpha and Thalattosauria as opposed to the Pantestudine relations.

[16][17][18] Although the most diverse clade of living archosauromorphs are birds, early members of the group were evidently reptilian, superficially similar to modern lizards.

When archosauromorphs first appeared in the fossil record in the Permian, they were represented by long-necked, lightly built sprawling reptiles with moderately long, tapering snouts.

Other early groups such as trilohpsaurids, azendohsaurids, and rhynchosaurs deviate from this body plan by evolving into stockier forms with semi-erect postures and higher metabolisms.

[1] Most archosauromorphs more "advanced" than Protorosaurus possessed an adaptation of the premaxilla (tooth-bearing bone at the tip of the snout) known as a posterodorsal or postnarial process.

A few advanced archosauriforms reacquired the plesiomorphic ("primitive") state present in other reptiles, that being a short or absent posterodorsal process of the premaxilla, with the rear edge of the nares formed primarily by the maxilla bones instead.

[4] Many early archosauromorphs, including Protorosaurus, tanystropheids, Trilophosaurus, and derived rhynchosaurs, have a blade-like sagittal crest on the parietal bones at the rear part of the skull roof, between a pair of holes known as the supratemporal (or upper temporal) fenestrae.

He also noted that in almost all early archosauromorphs (and some choristoderes), the parietal bones have an additional lowered area which extends transversely (from left to right) behind the supratemporal fenestrae and sagittal crest (when applicable).

On the other hand, the rear branch jugal bone lengthens to fill some of the space left by the shortening of the anterior process of the quadratojugal.

[19] Thin, plate-like ridges known as laminae develop to connect the vertebral components, sloping down from the elongated transverse processes to the centra.