Protorosauria is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

polyphyletic group of archosauromorph reptiles from the latest Middle Permian ( Capitanian stage) to the end of the Late Triassic (

Rhaetian The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest age ...

stage) of Asia, Europe and

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

. It was named by the English anatomist and paleontologist Thomas Henry Huxley in

1871 Events January–March * January 3 – Franco-Prussian War – Battle of Bapaume: Prussians win a strategic victory. * January 18 – Proclamation of the German Empire: The member states of the North German Confederation and the sout ...

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 In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...

, which have ribs that extend backward to the vertebrae behind them. Protorosaurs also have a gap between the quadrate bones and the

jugal bone The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...

s in the back of the skull near the jaw joint, making their skulls resemble those of

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...

s. While previously thought to be

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

, the group is now though to consist of various groups of basal archosauromorph reptiles that lie outside

Crocopoda Archosauromorpha (Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) rather than lepidosaurs (such as tuataras, lizards, ...

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 In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

taxon. ''Protorosaurus'', ''

Macrocnemus ''Macrocnemus'' is an extinct genus of archosauromorph reptile known from the Middle Triassic (Late Anisian to Ladinian) of Europe and China. ''Macrocnemus'' is a member of the Tanystropheidae family and includes three species''. Macrocnemus bass ...

'', tanystropheids, and various other protorosaurs are usually placed near the base of Archosauromorpha, while '' Prolacerta'' and ''

Pamelaria ''Pamelaria'' is an extinct genus of allokotosaurian archosauromorph reptile known from a single species, ''Pamelaria dolichotrachela'', from the Middle Triassic of India. ''Pamelaria'' has sprawling legs, a long neck, and a pointed skull with no ...

'', two

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

n Triassic protorosaurs, are now thought to be in a more

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

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 A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

containing taxa such as '' Protorosaurus'', ''

'', 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 Tanystropheidae is an extinct family of mostly marine archosauromorph reptiles that lived throughout the Triassic Period. They are characterized by their long, stiff necks formed from elongated cervical vertebrae with very long cervical ribs. So ...

(and relatives). However, some analysis found ''Protorosaurus'' (and sometimes the closely related ''

Czatkowiella ''Czatkowiella'' is an extinct genus of long-necked archosauromorph known from Early Triassic (Olenekian age) rocks of Czatkowice 1, Poland. It was first named by Magdalena Borsuk−Białynicka and Susan E. Evans in 2009 and the type species is ' ...

'') 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 ''

''. A wide variety of Permian and Triassic reptiles have been classified within Protorosauria, including the arboreal gliding reptile ''

Sharovipteryx ''Sharovipteryx'' ("Sharov's wing", known until 1981 as ''Podopteryx'', "foot wing"), is a genus of early gliding reptiles containing the single species ''Sharovipteryx mirabilis''. It is known from a single fossil and is the only glider with a m ...

'' and the aquatic

tanystropheid Tanystropheidae is an extinct family of mostly marine archosauromorph reptiles that lived throughout the Triassic Period. They are characterized by their long, stiff necks formed from elongated cervical vertebrae with very long cervical ribs. Som ...

s, which have extremely long necks. Another enigmatic group of Triassic reptiles, the

Drepanosauromorpha Drepanosaurs (members of the clade Drepanosauromorpha) are a group of extinct reptiles that lived between the Carnian and Rhaetian stages of the late Triassic Period, approximately between 230 and 210 million years ago. The various species of dre ...

, 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

group of

archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...

s. While Senter (2004) reassigned the bizarre, arboreal drepanosaurids and ''

Longisquama ''Longisquama'' is a genus of extinct reptile. There is only one species, ''Longisquama insignis'', known from a poorly preserved skeleton and several incomplete fossil impressions from the Middle to Late Triassic Madygen Formation in Kyrgyzst ...

'' 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).

References

{{Taxonbar, from=Q133072 Prehistoric archosauromorphs Permian reptiles Triassic reptiles Paraphyletic groups Fossil taxa described in 1871 Taxa named by Thomas Henry Huxley