Protorosauria was considered to be a synonym of Prolacertiformes for many years. Since 1998, many phylogenetic analyses have found Protorosauria, as used in its widest sense, to be a polyphyletic or paraphyletic taxon. Protorosaurus, Macrocnemus, tanystropheids, and various other protorosaurs are usually placed near the base of Archosauromorpha, while Prolacerta and Pamelaria, two Gondwanan Triassic protorosaurs, are now thought to be in a more derived position as close relatives of Archosauriformes. Most phylogenetic analyses since 1998 have found a strongly supported clade that includes only the genus Prolacerta and the Archosauriformes. For this reason Prolacerta, Pamelaria, and several other related forms have been removed from Protorosauria. Because the name Prolacertiformes is defined based on the genus Prolacerta, the name Protorosauria is used for the remaining group. Only recently has Protorosauria been defined in a phylogenetic sense as the most inclusive clade containing taxa such as Protorosaurus, Macrocnemus, and Tanystropheus. Analyses, such as Dilkes, Sues, Modesto & Sues, Rieppel, Fraser & Nosotti, Rieppel, Li & Fraser, Gottmann-Quesada and Sander and Renesto et al., recovered a large Protorosauria, that includes Protorosaurus, Drepanosauridae and Tanystropheidae. However, some analysis found Protorosaurus to be more advanced or more basal than the node Drepanosauridae+Tanystropheidae, but always more basal than Prolacerta. Some studies still use the term Prolacertiformes to include prolacertids and traditional protorosaurs, while restricting the term Protorosauria to the smallest clade that includes Protorosaurus, Macrocnemus, and Tanystropheus; thus Protorosauria is a true clade, while Prolacertiformes is an evolutionary grade of early archosauromorphs. Pritchard et al., Nesbitt et al., and Ezcurra found that even this definition of Protorosauria, like Prolacertiformes, was an unnatural group of various non-Crocopodan archosauromorphs. These studies found that tanystropheids were archosauromorphs more closely related to crocopods than to Protorosaurus. Nevertheless, Ezcurra noted that archosauromorph systematics required further study, and that phylogenetic support for Protorosauria being a natural group was only barelyweaker than the support for the group being unnatural
Included groups
The Protorosauria includes the Permian genus Protorosaurus, closely related to Czatkowiella. A widevariety of Permian and Triassic reptiles have been classified within Protorosauria, including the arboreal gliding reptile Sharovipteryx and the aquatic tanystropheids, which have extremely long necks. Another enigmatic group of Triassic reptiles, the Drepanosauromorpha, have often been classified as belonging to the Protorosauria. Pterosaurs have also been proposed as protorosaurs or close relatives of them, although they are now regarded as a more derived group of archosaurs. While Senter reassigned the bizarre, arboreal drepanosaurids and Longisquama to a group of more primitive diapsids called Avicephala, subsequent studies failed to find the same result, instead supporting the hypothesis that they were protorosaurs.
