Protorosauria is an extinct

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

group of

archosauromorph 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, l ...

reptiles from the latest

Middle Permian The Guadalupian is the second and middle series/ epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± ...

(

Capitanian In the geologic timescale, the Capitanian is an age or stage of the Permian. It is also the uppermost or latest of three subdivisions of the Guadalupian Epoch or Series. The Capitanian lasted between and million years ago. It was preceded by ...

stage) to the end of the

Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...

( Rhaetian stage) of

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...

and North America. It was named by the English

anatomist Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having it ...

and

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Thomas Henry Huxley Thomas Henry Huxley (4 May 1825 – 29 June 1895) was an English biologist and anthropologist specialising in comparative anatomy. He has become known as "Darwin's Bulldog" for his advocacy of Charles Darwin's theory of evolution. The stori ...

in 1871 as an order, originally to solely contain ''

Protorosaurus ''Protorosaurus'' ("first lizard") is a genus of lizard-like early reptiles. Members of the genus lived during the late Permian period in what is now Germany and Great Britain. Once believed to have been an ancestor to lizards, ''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 The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels. The sternum, together known as the thoracic cage, is a semi- ...

that extend backward to the vertebrae behind them. Protorosaurs also have a gap between the

quadrate bone The quadrate bone is a skull bone in most tetrapods, including amphibians, sauropsids (reptiles, birds), and early synapsids. In most tetrapods, the quadrate bone connects to the quadratojugal and squamosal bones in the skull, and forms upper pa ...

s 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. Anato ...

s 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 though to consist of various groups of basal archosauromorph reptiles that lie outside Crocopoda.

Classification

Protorosauria was considered to be a synonym of

Prolacertiformes Protorosauria is an extinct polyphyletic group of 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 anatom ...

for many years. Since 1998, many phylogenetic analyses have found Protorosauria, as used in its widest sense, to be a

or paraphyletic taxon. ''Protorosaurus'', '' Macrocnemus'', tanystropheids, and various other protorosaurs are usually placed near the base of Archosauromorpha, while ''

Prolacerta ''Prolacerta'' is a genus of archosauromorph from the lower Triassic of South Africa and Antarctica. The only known species is ''Prolacerta broomi''. The generic name ''Prolacerta'' is derived from Latin meaning “before lizard” and its spec ...

'' and '' Pamelaria'', two Gondwanan Triassic protorosaurs, are now thought to be in a more derived position as close relatives of

Archosauriformes Archosauriformes (Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles that developed from archosauromorph ancestors some time in the Latest Permian (roughly 252 million years ago). It was defined by Jacques Gauthier ...

. Most

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analyses since 1998 have found a strongly supported clade that includes only the genus ''

'' and the

. 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

sense as the most inclusive clade containing taxa such as ''

'', '' Macrocnemus'', and ''

Tanystropheus ''Tanystropheus'' (Greek ~ 'long' + 'hinged') is an extinct archosauromorph reptile from the Middle and Late Triassic epochs. It is recognisable by its extremely elongated neck, which measured long—longer than its body and tail combined. T ...

''. 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 ''

'', 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 A grade is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit. Definition An evolutionary grade is a group of sp ...

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 ''

'', 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 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 ...

, have often been classified as belonging to the Protorosauria.

Pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 ...

s 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 ''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

diapsid Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years a ...

s called

Avicephala Avicephala ("bird heads") is an extinct, potentially polyphyletic grouping of diapsid reptiles that lived during the Late Permian and Triassic periods characterised by superficially bird-like skulls and arboreal lifestyles. As a clade, Avicephala ...

, subsequent studies failed to find the same result, instead supporting the hypothesis that they were protorosaurs.

Cladogram

The following

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

shows the position of Protorosauria among the

Sauria Sauria is the clade containing the most recent common ancestor of archosaurs (such as crocodilians, dinosaurs, etc.) and lepidosaurs ( lizards and kin), and all its descendants. Since most molecular phylogenies recover turtles as more closely ...

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