Protorosauria

{{Automatic taxobox

| name = Protorosaurs

| fossil_range = Latest Middle Permian - Late Triassic,
{{fossil_range|260|201.3}}

| image = Protorosaurus speneri fossil.jpg

| image_caption = Fossil specimen of Protorosaurus speneri, Teyler's Museum

| image2 = Tanysaurian Skeletal Reconstructions.png

| image2_caption = Skeletal reconstructions of various members of Tanysauria, including Trachelosaurus fischeri, Dinocephalosaurus orientalis, Tanystropheus hydroides, and Tanystropheus longobardicus

| taxon = Protorosauria

| authority = Huxley, 1871

| subdivision_ranks = Subtaxa

| subdivision = * {{extinct}}Czatkowiella

{{extinct}}Exilisuchus?
{{extinct}}Jesairosaurus
{{extinct}}Malutinisuchus
{{extinct}}Mecistotrachelos?
{{extinct}}Megacnemus
{{extinct}}Microcnemus
{{extinct}}Protorosaurus
{{extinct}}Rhombopholis
{{extinct}}Tanysauria
{{extinct}}Sharovipterygidae?
{{extinct}}Trachelosauridae
{{extinct}}Tanystropheidae

}}

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.{{cite book |last1=Sues |first1=H.-D. |last2=Fraser |first2=N.C. |year=2010 |chapter=Early and early Middle Triassic in Gondwana |title=Triassic Life on Land: The Great Transition |publisher=Columbia University Press |location=New York |isbn=9780231135221}}

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.{{Cite journal |last1=Simões |first1=T. R. |last2=Kammerer |first2=C. F. |last3=Caldwell |first3=M. W. |last4=Pierce |first4=S. E. |year=2022 |title=Successive climate crises in the deep past drove the early evolution and radiation of reptiles |journal=Science Advances |volume=8 |issue=33 |pages=eabq1898 |doi=10.1126/sciadv.abq1898 |pmc=9390993 |pmid=35984885 |doi-access=free}} 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.

Classification

Protorosauria was considered to be a synonym of Prolacertiformes for many years.{{cite journal |last1=Benton |first1=M.J. |last2=Allen |first2=J.L. |year=1997 |title=Boreopricea from the Lower Triassic of Russia, and the relationships of the prolacertiform reptiles |journal=Palaeontology |volume=40 |issue=4 |pages=931–953 |url=https://www.palass.org/sites/default/files/media/publications/palaeontology/volume_40/vol40_part4_pp931-953.pdf }}

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.{{cite journal |last1=Gottmann-Quesada |first1=A. |last2=Sander |first2=P.M. |year=2009 |title=A redescription of the early archosauromorph Protorosaurus speneri Meyer, 1832, and its phylogenetic relationships |journal=Palaeontographica Abteilung A |volume=287 |issue=4–6 |pages=123–200 |doi=10.1127/pala/287/2009/123}} Most phylogenetic analyses since 1998 have found a strongly supported clade that includes only the genus Prolacerta and the Archosauriformes.{{Cite journal | last1 = Modesto | first1 = S. P. | last2 = Sues | first2 = H. D. | doi = 10.1111/j.1096-3642.2003.00102.x | title = The skull of the Early Triassic archosauromorph reptile Prolacerta broomi and its phylogenetic significance | journal = Zoological Journal of the Linnean Society | volume = 140 | issue = 3 | pages = 335–351 | year = 2004 | url = https://zenodo.org/record/5428881 | doi-access = free }}

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),{{cite journal |first=David M. |last=Dilkes |year=1998 |title=The Early Triassic rhynchosaur Mesosuchus browni and the interrelationships of basal archosauromorph reptiles |journal=Philosophical Transactions of the Royal Society of London, Series B |volume=353 |issue= 1368|pages=501–541 |doi=10.1098/rstb.1998.0225|pmc=1692244 }}{{cite journal |last=Sues |first=H.-D. |year=2003 |title=An unusual new archosauromorph reptile from the Upper Triassic Wolfville Formation of Nova Scotia |journal=Canadian Journal of Earth Sciences |volume=40 |issue=4 |pages=635–649 |doi= 10.1139/e02-048|bibcode=2003CaJES..40..635S }}{{Cite journal | last1 = Rieppel | first1 = O. | last2 = Li | first2 = C. | last3 = Fraser | first3 = N. C. | title = The skeletal anatomy of the triassic protorosaur Dinocephalosaurus orientalis Li, from the Middle Triassic of Guizhou Province, southern China | journal = Journal of Vertebrate Paleontology | volume = 28 | pages = 95–110| year = 2008 | doi = 10.1671/0272-4634(2008)28[95:TSAOTT]2.0.CO;2 | s2cid = 86026836 }}{{cite journal | last1 = Renesto | first1 = Silvio | last2 = Spielmann | first2 = Justin A. | last3 = Lucas | first3 = Spencer G. | last4 = Tarditi Spagnoli | first4 = Giorgio | year = 2010 | title = The taxonomy and paleobiology of the Late Triassic (Carnian-Norian: Adamanian-Apachean) drepanosaurs (Diapsida: Archosauromorpha: Drepanosauromorpha) | journal = New Mexico Museum of Natural History and Science Bulletin | volume = 46 | pages = 1–81 }} 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{{Cite journal | last1 = Li | first1 = C. | last2 = Rieppel | first2 = O. | last3 = Labarbera | first3 = M. C. | doi = 10.1126/science.1100498 | title = A Triassic Aquatic Protorosaur with an Extremely Long Neck | journal = Science | volume = 305 | issue = 5692 | pages = 1931 | year = 2004 | pmid = 15448262| s2cid = 38739295 }} or more basal{{Cite journal|first1=Magdalena |last1=Borsuk−Białynicka |first2=Susan E. |last2=Evans|year=2009|title=A long−necked archosauromorph from the Early Triassic of Poland|journal=Paleontologica Polonica|volume=65|pages=203–234|url=http://palaeontologia.pan.pl/PP65/PP65_203-234.pdf}} 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.{{Cite journal | last1 = Hone | first1 = D. W. E. | last2 = Benton | first2 = M. J. | doi = 10.1017/S1477201907002064 | title = An evaluation of the phylogenetic relationships of the pterosaurs among archosauromorph reptiles | journal = Journal of Systematic Palaeontology | volume = 5 | issue = 4 | pages = 465–469 | year = 2007 | s2cid = 86145645 }}

Pritchard et al. (2015),{{Cite journal|last1=Pritchard|first1=Adam C.|last2=Turner|first2=Alan H.|last3=Nesbitt|first3=Sterling J.|last4=Irmis|first4=Randall B.|last5=Smith|first5=Nathan D.|date=2015-03-04|title=Late Triassic tanystropheids (Reptilia, Archosauromorpha) from northern New Mexico (Petrified Forest Member, Chinle Formation) and the biogeography, functional morphology, and evolution of Tanystropheidae|journal=Journal of Vertebrate Paleontology|volume=35|issue=2|pages=e911186|doi=10.1080/02724634.2014.911186|s2cid=130089407|issn=0272-4634}} Nesbitt et al. (2015),{{Cite journal|last1=J.|first1=Nesbitt, Sterling|last2=Flynn|first2=John J.|last3=Pritchard|first3=Adam C.|first4=Parrish|last4=J. Michael|last5=Lovasoa|first5=Ranivoharimanana|last6=Wyss|first6=André R.|date=2015-12-07|title=Postcranial osteology of Azendohsaurus madagaskarensis (?Middle to Upper Triassic, Isalo Group, Madagascar) and its systematic position among stem archosaur reptiles. (Bulletin of the American Museum of Natural History, no. 398)|language=en-US|hdl=2246/6624}} Ezcurra (2016){{Cite journal|last=Ezcurra|first=Martín D.|date=2016-04-28|title=The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms|journal=PeerJ|language=en|volume=4|doi=10.7717/peerj.1778|issn=2167-8359|pmc=4860341|pmid=27162705|page=e1778 |doi-access=free }} and Spiekman et al., 2021{{Cite journal|last1=Spiekman|first1=Stephan N. F.|last2=Fraser|first2=Nicholas C.|last3=Scheyer|first3=Torsten M.|date=2021-05-03|title=A new phylogenetic hypothesis of Tanystropheidae (Diapsida, Archosauromorpha) and other "protorosaurs", and its implications for the early evolution of stem archosaurs|journal=PeerJ|language=en|volume=9|pages=e11143|doi=10.7717/peerj.11143 |pmid=33986981| pmc=8101476|issn=2167-8359|doi-access=free}} 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.{{cite journal |last=Borsuk–Białynicka |first=M. |author2=Evans, S.E. |year=2009 |title=A long–necked archosauromorph from the Early Triassic of Poland |url=http://palaeontologia.pan.pl/PP65/PP65_203-234.pdf |journal=Palaeontologia Polonica |volume=65 |pages=203–234}} 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.{{cite journal | last1 = Renesto | first1 = S | year = 1994 | title = Megalancosaurus, a possibly arboreal archosauromorph (Reptilia) from the Upper Triassic of northern Italy | journal = Journal of Vertebrate Paleontology | volume = 14 | issue = 1| pages = 38–52 | doi=10.1080/02724634.1994.10011537}}

Pterosaurs have also been proposed as protorosaurs or close relatives of them,{{cite journal | last1 = Peters | first1 = D | year = 2000 | title = A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis | journal = Rivista Italiana di Paleontologia e Stratigrafia | volume = 106 | issue = 3| pages = 293–336 }} 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,{{cite journal | last1 = Senter | first1 = P | year = 2004 | title = Phylogeny of Drepanosauridae (Reptilia: Diapsida) | journal = Journal of Systematic Palaeontology | volume = 2 | issue = 3| pages = 257–268 | doi = 10.1017/S1477201904001427 | s2cid = 83840423 }} 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).

{{clade| style=font-size:100%;line-height:85%

|1={{clade

|1=Petrolacosaurus

|2={{clade

|1=Youngina

|2={{clade

|label1=Choristodera

|1={{clade

|1=Lazarussuchus

|2={{clade

|1=Champsosaurus

|2=Cteniogenys }} }}

|label2=Sauria

|2={{clade

|label1=Lepidosauromorpha

|1={{clade

|1=Gephyrosaurus

|2=Squamata }}

|label2=Archosauromorpha

|2={{clade

|label1=Protorosauria

|1={{clade

|1=Protorosaurus

|label2=Drepanosauridae

|2={{clade

|1=Drepanosaurus

|2=Megalancosaurus }}

|label3=Tanystropheidae

|3={{clade

|1=Macrocnemus

|2={{clade

|1=Langobardisaurus

|2=Tanystropheus longobardicus }} }} }}

|2={{clade

|1=Trilophosaurus

|2={{clade

|label1=Rhynchosauria

|1={{clade

|1=Howesia

|2=Mesosuchus }}

|2={{clade

|1=Prolacerta

|label2=Archosauriformes

|2={{clade

|1=Proterosuchus

|2=Euparkeria }} }} }} }} }} }} }} }} }} }}

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

|1=Araeoscelidia

|label2=Neodiapsida

|2={{clade

|1=Orovenator

|2={{clade

|1=Claudiosaurus

|2={{clade

|1=Acerosodontosaurus

|2={{clade

|1=Youngina

|label2=Sauria

|2={{clade

|1=Lepidosauromorpha

|grouplabel2="Protorosauria"

|label2=Archosauromorpha

|2={{clade

|1=Jesairosaurus |barbegin1=green

|2={{clade

|1=Protorosaurus |bar1=green

|2={{clade

|1=Prolacerta |bar1=green

|2={{clade

|1={{clade

|1=Czatkowiella |bar1=green

|2=Sharovipterygidae (Ozimek) |bar2=green}}

|2={{clade

|1=Fuyuansaurus |bar1=green

|label2=Dinocephalosauridae

|2={{clade

|1=Protanystropheus |bar1=green

|2=Pectodens |bar2=green

|3=Dinocephalosaurus |bar3=green}}}} }}

|label2=Tanystropheidae

|2={{clade

|1={{clade

|1=Macrocnemus bassanii |bar1=green

|2=Macrocnemus fuyuanensis |bar2=green }}

|2={{clade

|1={{clade

|1=Augustaburiania |bar1=green

|2=Amotosaurus |bar2=green}}

|2={{clade

|1=Langobardisaurus |bar1=green

|2=AMNH FARB 7206 |bar2=green

|3={{clade

|1=Sclerostropheus |bar1=green

|2={{clade

|1=Tanystropheus hydroides |bar1=green

|2=GMPKU P 1527 T. cf. hydroides |bar2=green

|3=Tanystropheus longobardicus |barend3=green }}}}}}}}}}}}

|label2=Crocopoda

|2={{clade

|1=Allokotosauria

|2={{clade

|1=Rhynchosauria

|2={{clade

|1=Teyujagua

|2=Archosauriformes}}}}}}}}}}}}}}}}}}}}}}}}}}|style=font-size:85%;line-height:85%|label1=Diapsida}}

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.{{Cite journal |last1=Spiekman |first1=Stephan N. F. |last2=Ezcurra |first2=Martín D. |last3=Rytel |first3=Adam |last4=Wang |first4=Wei |last5=Mujal |first5=Eudald |last6=Buchwitz |first6=Michael |last7=Schoch |first7=Rainer R. |date=2024-03-15 |title=A redescription of Trachelosaurus fischeri from the Buntsandstein (Middle Triassic) of Bernburg, Germany: the first European Dinocephalosaurus-like marine reptile and its systematic implications for long-necked early archosauromorphs |journal=Swiss Journal of Palaeontology |volume=143 |issue=1 |pages=10 |doi=10.1186/s13358-024-00309-6 |issn=1664-2384 |doi-access=free}}{{clade|{{clade

|label1=Archosauromorpha

|1={{clade

|1=Protorosaurus

|2=Aenigmastropheus }}

|3={{clade

|2=Crocopoda

|label1=Tanysauria

|1={{clade

|1=Jesairosaurus

|2={{clade

|label1=Trachelosauridae

|1={{clade