Biology:Protorosauria

Protorosauria is an extinct, likely paraphyletic group of basal archosauromorph reptiles from the latest Middle Permian (Capitanian stage) to the end of the Late Triassic (Rhaetian stage) of Asia, Europe and North America. It was named by the English anatomist and paleontologist Thomas Henry Huxley in 1871 as an order, originally to solely contain Protorosaurus. Other names which were once considered equivalent to Protorosauria include Prolacertiformes and Prolacertilia.

Protorosaurs are distinguished by their long necks formed by elongated cervical vertebrae, which have ribs that extend backward to the vertebrae behind them. Protorosaurs also have a gap between the quadrate bones and the jugal bones in the back of the skull near the jaw joint, making their skulls resemble those of lizards. While previously thought to be monophyletic, the group is now thought to consist of various groups of basal archosauromorph reptiles that lie outside Crocopoda, though some recent studies have recovered the group as monophyletic. A number of members of Protorosauria have been found to belong to a monophyletic group (though not including Protorosaurus) which was named Tanysauria in 2024.. In 2026. Jenkins et al found strong support on morphological grounds for Pantestudines to be nested within Archosauromorpha, with its ancestor being "protosaurian"-like, which is supported by some anatomical features of early Pantestudines.

Classification

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 (collectively called prolacertids) 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 (1998), Sues (2003), Modesto & Sues (2004), Rieppel, Fraser & Nosotti (2003), Rieppel, Li & Fraser (2008), Gottmann-Quesada and Sander (2009) and Renesto et al. (2010), recovered a large Protorosauria, that includes Protorosaurus, Drepanosauridae (and relatives) and Tanystropheidae (and relatives). However, some analysis found Protorosaurus (and sometimes the closely related Czatkowiella) 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. (2015), Nesbitt et al. (2015), Ezcurra (2016) and Spiekman et al., 2021 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 barely weaker than the support for the group being unnatural.

Included groups

The Protorosauria includes the Permian genus Protorosaurus, closely related to Czatkowiella. A wide variety 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 (2004) 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.

Cladogram

The following cladogram shows the position of Protorosauria among the Sauria sensu Sean P. Modesto and Hans-Dieter Sues (2004).

Petrolacosaurus       Youngina     Choristodera   Lazarussuchus       Champsosaurus     Cteniogenys       Sauria Lepidosauromorpha   Gephyrosaurus     Squamata     Archosauromorpha Protorosauria   Protorosaurus   Drepanosauridae   Drepanosaurus     Megalancosaurus     Tanystropheidae   Macrocnemus       Langobardisaurus     Tanystropheus longobardicus             Trilophosaurus     Rhynchosauria   Howesia     Mesosuchus         Prolacerta   Archosauriformes   Proterosuchus     Euparkeria

Most recent studies have recovered Protorosauria as a whole as a paraphyletic, cladogram after Spiekman et al. 2021

Diapsida

Araeoscelidia   Neodiapsida   Orovenator       Claudiosaurus       Acerosodontosaurus       Youngina   Sauria   Lepidosauromorpha   Archosauromorpha   Jesairosaurus       Protorosaurus       Prolacerta             Czatkowiella     Sharovipterygidae (Ozimek)         Fuyuansaurus   Dinocephalosauridae   Protanystropheus     Pectodens     Dinocephalosaurus         Tanystropheidae     Macrocnemus bassanii     Macrocnemus fuyuanensis           Augustaburiania     Amotosaurus         Langobardisaurus     AMNH FARB 7206       Sclerostropheus       Tanystropheus hydroides     GMPKU P 1527 T. cf. hydroides     Tanystropheus longobardicus               Crocopoda   Allokotosauria       Rhynchosauria       Teyujagua     Archosauriformes               "Protorosauria"

Although Protorosauria as a whole is often found to be a paraphyletic, a large group of former "protorosaurs" (excluding Protorosaurus) is frequently found to be monophyletic. This clade was given the name "Tanysauria" by Spiekman et al. in 2024.

Archosauromorpha     Protorosaurus     Aenigmastropheus       Tanysauria   Jesairosaurus     Trachelosauridae     Austronaga     Pectodens         Fuyuansaurus       Trachelosaurus       Gracilicollum     Dinocephalosaurus           Tanystropheidae   Augustaburiania     Luxisaurus         Macrocnemus bassanii       Macrocnemus fuyuanensis     Macrocnemus obristi           UFRGS-PV-492-T       Amotosaurus       Langobardisaurus         Raibliania     Tanystropheus spp.         Sclerostropheus       Ozimek     Tanytrachelos                         Crocopoda

Jenkins et al, 2026 found strong support on morphological grounds for Pantestudines to be nested within Archosauromorpha, more closely related to modern archosaurs than to classic early archosauromorph Protorosaurus, suggesting that the ancestor of Pantestudines was "protosaurian"-like, which is supported by some anatomical features of early Pantestudines. They also found Eunotosaurus to be a millerettid stem-reptile unrelated to Pantestudines.

Sauropsida

†Araeoscelidia 70px       †Bolosauridae 70px     †Ankyramorpha   †Acleistorhinidae 70px   †Procolophonia   †Pareiasauromorpha 70px     †Procolophonoidea 70px           †Mesosauria 70px         †Ascendonanus     †Orovenator     †Cabarzia     Parapleurota   †Millerettidae (including Eunotosaurus) 70px   Neodiapsida   †Saurosternon       †Younginidae 70px       †Tangasauridae 70px       †Claudiosaurus 70px       †Weigeltisauridae 70px     †Drepanosauromorpha 70px   Sauria   Lepidosauromorpha 100px   Archosauromorpha   †Sauropterygia (including Plesiosauria) 70px       †Protorosaurus 100px   Archelosauria   Pantestudines 70px       †Tanystropheidae 70px       †Prolacerta 70px       †Allokotosauria 70px       †Rhynchosauria 70px       †Teyujagua     Archosauriformes (including Archosauria)                   Reptilia s. s.

References

Template:Archosauromorpha Wikidata ☰ Q133072 entry