It was named by the English anatomist and paleontologist Thomas Henry Huxley in 1871 as an order, originally to solely contain Protorosaurus.

[3] A number of members of Protosauria have been found to belong to a monophyletic group (though not including Protorosaurus) which was named Tanysauria in 2024.

Only recently has Protorosauria been defined in a phylogenetic sense as the most inclusive clade containing taxa such as Protorosaurus, Macrocnemus, and Tanystropheus.

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.

While Senter (2004) reassigned the bizarre, arboreal drepanosaurids and Longisquama to a group of more primitive diapsids called Avicephala,[21] subsequent studies failed to find the same result, instead supporting the hypothesis that they were protorosaurs.

[7] Petrolacosaurus Youngina Lazarussuchus Champsosaurus Cteniogenys Gephyrosaurus Squamata Protorosaurus Drepanosaurus Megalancosaurus Macrocnemus Langobardisaurus Tanystropheus longobardicus Trilophosaurus Howesia Mesosuchus Prolacerta Proterosuchus Euparkeria

Most recent studies have recovered Protorosauria as a whole as a paraphyletic, cladogram after Spiekman et al. 2021[2]Araeoscelidia Orovenator Claudiosaurus Acerosodontosaurus Youngina Lepidosauromorpha Jesairosaurus Protorosaurus Prolacerta Czatkowiella Sharovipterygidae (Ozimek) Fuyuansaurus Protanystropheus Pectodens Dinocephalosaurus Macrocnemus bassanii Macrocnemus fuyuanensis Augustaburiania Amotosaurus Langobardisaurus