{{Short description|Clade of reptiles}} {{Automatic taxobox | name = Crurotarsans | fossil_range = <br>Early Triassic–Present, {{Fossil range|248|0}} | image = Protome_batalaria.jpg | image_caption = Life restoration of ''Protome batalaria'', a phytosaur | image2 = Ornithosuchus_BW.jpg | image2_caption = Life restoration of ''Ornithosuchus woodwardi'', a pseudosuchian archosaur | taxon = Crurotarsi | authority = Sereno & Arcucci, 1990 | subdivision_ranks = Subgroups | subdivision = * {{extinct}}''Omosaurus'' * {{extinct}}Phytosauria *Archosauria ** Avemetatarsalia ** Pseudosuchia }}
'''Crurotarsi''' is a clade of archosauriform reptiles that includes crocodilians and stem-crocodilians and possibly bird-line archosaurs too if the extinct, crocodile-like phytosaurs are more distantly related to crocodiles than traditionally thought.<ref name=NSJ11/> Prior to 2011, the group had invariably included only archosaurs closer to crocodilians than to birds and other dinosaurs. An equivalent term for the crocodilian side of the archosaur family tree is Pseudosuchia. This traditional definition of Crurotarsi assumed that phytosaurs were crown-group archosaurs and more closely related to crocodilians than to birds. However, a 2011 study argued that the phytosaur lineage evolved prior to the split between birds and crocodilians. This would mean that phytosaurs were not true archosaurs, and therefore could not be considered representatives of croc-line archosaurs.<ref name="NSJ11" />
The name Crurotarsi is derived from the Latin word ''crus'' (lower leg) and the Greek word ''tarsos'' (ankle). It refers to the specialized articulation (a crurotarsal joint) between the lower leg (specifically the fibula) and the ankle (specifically the calcaneum) which is present in the skeletons of reptiles such as suchians and phytosaurs. In their ankle joint, a hemicylindrical condyle on the calcaneum articulates into a concave area on the fibula.<ref name="sereno1990" /><ref>{{cite journal|last= Sereno|first=Paul|year=1991|title=Basal archosaurs: phylogenetic relationships and functional implications|journal=Journal of Vertebrate Paleontology|volume=11 | issue = Suppl. 4|pages=1–51|doi=10.1080/02724634.1991.10011426 }}</ref>
==Taxonomic history== The name Crurotarsi was erected as a node-based clade by Paul Sereno and A. B. Arcucci in 1990 to supplant the old term Pseudosuchia, but with a different definition.<ref name=sereno1990>{{cite journal | last1 = Sereno | first1 = P.C. | last2 = Arcucci | first2 = A.B. | year = 1990 | title = The monophyly of crurotarsal archosaurs and the origin of bird and crocodile ankle joints | journal = Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen | volume = 180 | pages = 21–52 }}</ref> Crurotarsi includes, by most published definitions, all descendants of the common ancestor of modern crocodiles, ornithosuchids, aetosaurs, and phytosaurs; Nesbitt (2011) provided a shorter definition, defining Crurotarsi as "the least inclusive clade containing ''Rutiodon carolinensis'' Emmons, 1856, and ''Crocodylus niloticus'' Laurenti, 1768".<ref name=NSJ11/> According to two studies published in 2011 by Nesbitt and coworkers, using either of these definitions leads to the inclusion of all other true archosaurs in Crurotarsi, due to the possibly basal phylogenetic position of the phytosaurs. This means that grouping the phytosaurs and crocodilians into a clade while excluding the avemetatarsalians (pterosaurs, dinosaurs, and birds) would result in a paraphyletic grouping. A more definitive group is Pseudosuchia, which is defined as all archosaurs closer to crocodiles than to birds (matching the traditional content of Crurotarsi).<ref name="NSJ11">{{cite journal|last=Nesbitt|first=S.J.|year=2011|title=The early evolution of archosaurs: relationships and the origin of major clades|url=https://digitallibrary.amnh.org/handle/2246/6112|journal=Bulletin of the American Museum of Natural History|volume=352|pages=1–292|doi=10.1206/352.1|hdl=2246/6112|s2cid=83493714|doi-access=free}}</ref><ref name=gauthieretal2011>{{cite journal | last1 = Gauthier | first1 = J. A. | last2 = Nesbitt | first2 = S. J. | last3 = Schachner | first3 = E. R. | last4 = Bever | first4 = G. S. | last5 = Joyce | first5 = W. G. | year = 2011 | title = The bipedal stem-crocodilian ''Poposaurus gracilis'': inferring function in fossils and innovation in archosaur locomotion | journal = Bulletin of the Peabody Museum of Natural History | volume = 52 | pages = 107–126 | doi=10.3374/014.052.0102| s2cid = 86687464 }}</ref>
==Phylogeny== Paul Sereno and A. B. Arcucci named Crurotarsi in 1990, defining it as "Parasuchia [phytosaurs], Ornithosuchidae, ''Prestosuchus'', Suchia, and all descendants of their common ancestor".<ref name=sereno1990/> The groups in this definition were considered crocodile-line archosaurs, as opposed to the bird-line archosaurs. Ornithosuchids were once considered bird-line archosaurs (as implied by their name, which means "bird crocodiles" in Greek), but were later recognized as crocodile-line archosaurs. This reclassification may have inspired Sereno's Crurotarsi, a node-based clade defined by the inclusion of ornithosuchids and other early archosaurs.
Two names were proposed for crocodile-line archosaurs before Crurotarsi was erected. The first, Pseudosuchia, was established as a stem-based clade in 1985.<ref name=GP85>{{cite book |last=Gauthier |first=J.A. |author2=Padian, K. |year=1985 |chapter=Phylogenetic, functional, and aerodynamic analyses of the origin of birds and their flight |title=The Beginnings of Birds |editor=Hecht, M.K. |editor2=Ostrom, J.H. |editor3=Viohl, G. |editor4=Wellnhofer, P. |publisher=Freunde des Jura-Museums |location=Eichstatt |pages=185–197}}</ref> It includes crocodiles and all archosaurs more closely related to crocodiles than to birds. The second, Crocodylotarsi, was named in 1988, possibly as a replacement for Pseudosuchia.<ref name=BC88>{{cite book |last=Benton |first=M.J. |author2=Clark, J.M. |year=1988 |chapter=Archosaur phylogeny and the relationships of the Crocodylia |title=Phylogeny and Classification of the Tetrapods |volume=1 |editor=Benton, M.J. |publisher=Clarendon Press |location=Oxford |pages=295–338}}</ref> The name Pseudosuchia, meaning "false crocodiles", has been used for over a century, and traditionally included aetosaurs. As a clade, Pseudosuchia includes the group Eusuchia, or "true crocodiles". Crocodylotarsi may have been named to remove confusion, but as a stem-based clade it is synonymous with Pseudosuchia. Because Pseudosuchia was named first, it has precedence. Crurotarsi traditionally contains the same archosaurs as Pseudosuchia, but as a node-based clade it is not synonymous.<ref name=BCA97>{{cite journal |last=Brochu |first=C.A. |year=1997 |title=Synonymy, redundancy, and the name of the crocodile stem-group |journal=Journal of Vertebrate Paleontology |volume=17 |issue=2 |pages=448–449 |doi=10.1080/02724634.1997.10010992}}</ref>
Below is a cladogram after Nesbitt & Norell (2006) and Nesbitt (2007) with Crurotarsi in its traditional sense encompassing just crocodile-line archosaurs:<ref name="Nesbitt & Norell, 2006">{{cite journal | last1 = Nesbitt | first1 = SJ | last2 = Norell | first2 = MA. | year = 2006 | title = Extreme convergence in the body plans of an early suchian (Archosauria) and ornithomimid dinosaurs (Theropoda) | journal = Proceedings of the Royal Society of London B: Biological Sciences | volume = 273 | issue = 1590| pages = 1045–1048 | doi=10.1098/rspb.2005.3426 | pmid=16600879 | pmc=1560254}}</ref><ref name="Nesbitt, 2007">{{cite journal | last1 = Nesbitt | first1 = S. | year = 2007 | title = The anatomy of ''Effigia okeeffeae'' (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa | url = http://digitallibrary.amnh.org/dspace/bitstream/2246/5840/1/B302.pdf | journal = Bulletin of the American Museum of Natural History | volume = 302 | page = 84 | doi=10.1206/0003-0090(2007)302[1:taoeoa]2.0.co;2| hdl = 2246/5840 }}</ref>
{{clade| style=font-size:90%;line-height:85% |label1='''Archosauriformes''' |1={{clade |1=†''Euparkeria''80 px |2={{clade |1=†Proterochampsidae80 px |label2=Archosauria |2={{clade |1=to Avemetatarsalia40 px |label2='''Crurotarsi''' |2={{clade |1=†Phytosauria80px |label2=Suchia |2={{clade |1=†Aetosauria80px |2={{clade |1='''Crocodylomorpha'''<span style="{{MirrorH}}">80px</span> |2={{clade |1=†Ornithosuchidae80 px |label2=Rauisuchia |2={{clade |1={{clade |1=†Rauisuchidae80px |2=†Prestosuchidae80px}} |label2="Group X" |2={{clade |1=†''Arizonasaurus''80px |2={{clade |1=†''Lotosaurus''80px |label2="Group Y" or Shuvosaurinae |2={{clade |1=†''Sillosuchus'' |2={{clade |1=†''Shuvosaurus''80px |2=†''Effigia''80px }} }} }} }} }} }} }} }} }} }} }} }} }}
Cladogram after Brusatte, Benton, Desojo and Langer (2010):<ref name="Brusatte, 2010">{{cite journal | last1 = Brusatte | first1 = Stephen L. | last2 = Benton | first2 = Michael J. | last3 = Desojo | first3 = Julia B. | last4 = Langer | first4 = Max C. | year = 2010 | title = The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida) | journal = Journal of Systematic Palaeontology | volume = 8 | issue = 1| pages = 3–47| doi = 10.1080/14772010903537732 | s2cid = 59148006 | url = https://www.pure.ed.ac.uk/ws/files/8232155/PDF_Brusatteetal2010ArchosaurPhylogeny.pdf | hdl = 20.500.11820/24322ff3-e80e-45f2-8d53-d35fd104195c | hdl-access = free }}</ref>
{{clade| style=font-size:90%;line-height:85% |label1='''Archosauriformes''' |1={{clade |1=†''Erythrosuchus''80 px |2={{clade |1=†''Euparkeria''80 px |2={{clade |1=†Proterochampsidae80 px |label2=Archosauria |2={{clade |1=to Avemetatarsalia40 px |label2='''Crurotarsi''' |2={{clade |1=†Phytosauria80px |label2=Suchia |2={{clade |1={{clade |1=†Aetosauria80px |label2=Paracrocodylomorpha |2={{clade |1=†''Gracilisuchus''80 px |label2=Bathyotica |2={{clade |1=†''Erpetosuchus''80 px |2='''Crocodylomorpha'''<span style="{{MirrorH}}">80px</span> }} }} }} |2={{clade |1={{clade |1=†''Revueltosaurus'' |2=†Ornithosuchidae80 px }} |label2=Rauisuchia |2={{clade |label1=†'''Rauisuchoidea''' |1={{clade |1={{clade |1=''Arganasuchus'' |2={{clade |1=''Fasolasuchus'' |2={{clade |1=''Stagonosuchus'' |2=''Ticinosuchus''80 px }} }} }} |2={{clade |label1=Prestosuchidae |1={{clade |1=''Saurosuchus''80 px |2={{clade |1=''Batrachotomus'' |2=''Prestosuchus''80px }} }} |label2=Rauisuchidae |2={{clade |1=''Tikisuchus'' |2={{clade |1=''Rauisuchus''80px |2={{clade |1=''Postosuchus''80px |2=''Teratosaurus'' }} }} }} }} }} |label2=†'''Poposauroidea''' |2={{clade |1=''Yarasuchus'' |2={{clade |1=''Qianosuchus'' |2={{clade |1=''Arizonasaurus''80px |2=''Bromsgroveia'' |3=''Lotosaurus''80px |4=''Poposaurus''80px |5=''Sillosuchus'' |label6='''Shuvosauridae''' |6={{clade |1=''Shuvosaurus''80px |2=''Effigia''80px }} }} }} }} }} }} }} }} }} }} }} }} }}
In 2011, Sterling J. Nesbitt found phytosaurs to be the sister taxon of Archosauria, and therefore not crocodile-line archosaurs. Because phytosaurs are included in the definition of Crurotarsi, this change in their phylogenetic placement expanded the scope of Crurotarsi, which therefore now includes phytosaurs, crocodiles, pterosaurs and dinosaurs. However, Pseudosuchia still contains only crocodile-line archosaurs.
Below is a cladogram modified from Nesbitt (2011) showing the new changes:<ref name=NSJ11/>
{{clade| style=font-size:90%;line-height:85% |label1=Archosauriformes |1={{clade |1=†Proterosuchidae80 px |2={{clade |1=†Erythrosuchidae80 px |2={{clade |1=†''Vancleavea''80 px |2={{clade |1=†Proterochampsia80 px |2={{clade |1=†''Euparkeria''80 px |label2='''Crurotarsi''' |2={{clade |1=†Phytosauria80px |label2='''Archosauria''' |2={{clade |1=Avemetatarsalia (bird-line archosaurs)40 px |label2=Pseudosuchia (crocodile-line archosaurs) |2={{clade |1=†Ornithosuchidae80 px |2=Suchia<span style="{{MirrorH}}">80px</span> }} }} }} }} }} }} }} }} }}
==References== {{Reflist|30em}}
*{{cite book|last=Benton|first=M. J.|title=Vertebrate Paleontology|year= 2004|edition=3rd|publisher=Blackwell Science|author-link=Michael Benton}} *{{cite web|publisher=Reuters|date=2008-09-12|last=Dunham|first=W.|title=Lucky break allowed dinosaurs to rule Earth |url=http://uk.reuters.com/article/uk-dinosaurs-idUKN1128337120080911 |archive-url=https://web.archive.org/web/20170816233157/http://uk.reuters.com/article/uk-dinosaurs-idUKN1128337120080911 |url-status=dead |archive-date=August 16, 2017 |access-date=2012-01-14}} *{{cite journal | last = Brusatte | first = S. L. | author2 = Benton, M. J. | author3 = Ruta, M. | author4 = Lloyd, G. T. | title = Superiority, Competition, and Opportunism in the Evolutionary Radiation of Dinosaurs | journal = Science | volume = 321 | issue = 5895 | pages = 1485–1488 | date = 2008-09-12 | url = http://palaeo.gly.bris.ac.uk/Benton/reprints/2008Science.pdf | doi = 10.1126/science.1161833 | access-date = 2012-01-14 | pmid = 18787166 | s2cid = 13393888 | archive-url = https://web.archive.org/web/20140624204033/http://palaeo.gly.bris.ac.uk/Benton/reprints/2008Science.pdf | archive-date = 2014-06-24 | url-status = dead | hdl = 20.500.11820/00556baf-6575-44d9-af39-bdd0b072ad2b | hdl-access = free }}
==External links== {{Wikispecies|Crurotarsi}} *[https://web.archive.org/web/20050306102719/http://www.palaeos.com/Vertebrates/Units/270Archosauromorpha/270.510.html Palaeos] *[https://web.archive.org/web/20081019121413/http://palaeo.gly.bris.ac.uk/benton/vertclass.html taxonomic hierarchy according to Benton 2004] *[http://www.helsinki.fi/~mhaaramo/metazoa/deuterostoma/chordata/archosauria/pseudosuchia/crurotarsi.html Mikko's Phylogeny]
{{Archosauromorpha|B.}} {{Taxonbar|from=Q131341}}
Category:Crurotarsans
Category:Archosauriformes Category:Tetrapod unranked clades Category:Triassic reptiles Category:Extant Early Triassic first appearances Category:Taxa named by Paul Sereno