Crurotarsi

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Crurotarsans
Temporal range:
Early TriassicPresent, 250–0 Ma
Protome batalaria.jpg
Life restoration of Protome batalaria
Ornithosuchus BW.jpg
Life restoration of Ornithosuchus woodwardi
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauriformes
Clade: Crurotarsi
Sereno & Arcucci, 1990
Subgroups

Crurotarsi is a group of archosauriform reptiles that includes the archosaurs (represented today by birds and crocodilians) and the extinct, crocodile-like phytosaurs.[1] The name is derived from the Latin word crus and the Greek word tarsos; it refers to the specialized articulation between crus and tarsus—specifically between fibula and calcaneum—present in the skeletons of suchians and phytosaurs, with a hemicylindrical condyle on the calcaneum articulating against fibula.[2][3]

Taxonomic history[edit]

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.[2] 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".[1] 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).[1][4]

Phylogeny[edit]

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".[2] 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.[5] 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.[6] 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.[7]

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:[1]

Archosauriformes 

ProterosuchidaeProterosuchusDB flipped.jpg

ErythrosuchidaeErythrosuchus africanus.jpg

VancleaveaVancleavea white background.jpg

ProterochampsiaPseudochampsa life restoration white background.jpg

EuparkeriaEuparkeria white background.png

 Crurotarsi 

PhytosauriaSmilosuchus adamanensis flipped.jpg

 Archosauria 

Avemetatarsalia (bird-line archosaurs)Meyers grosses Konversations-Lexikon - ein Nachschlagewerk des allgemeinen Wissens (1908) (Antwerpener Breiftaube).jpg

 Pseudosuchia (crocodile-line archosaurs) 

OrnithosuchidaeOrnithosuchus BW white background.jpg

SuchiaDescription des reptiles nouveaux, ou, Imparfaitement connus de la collection du Muséum d'histoire naturelle et remarques sur la classification et les caractères des reptiles (1852) (Crocodylus moreletii).jpg

Below is a cladogram after Nesbitt & Norell (2006) and Nesbitt (2007) with Crurotarsi in its traditional sense encompassing just crocodile-line archosaurs:[8][9]

Archosauriformes 

EuparkeriaEuparkeria white background.png

ProterochampsidaePseudochampsa life restoration white background.jpg

 Archosauria 

to AvemetatarsaliaMeyers grosses Konversations-Lexikon - ein Nachschlagewerk des allgemeinen Wissens (1908) (Antwerpener Breiftaube).jpg

Crurotarsi 

PhytosauriaSmilosuchus adamanensis flipped.jpg

 Suchia 

AetosauriaDesmatosuchus spurensis flipped.jpg

CrocodylomorphaDescription des reptiles nouveaux, ou, Imparfaitement connus de la collection du Muséum d'histoire naturelle et remarques sur la classification et les caractères des reptiles (1852) (Crocodylus moreletii).jpg

OrnithosuchidaeOrnithosuchus BW white background.jpg

 Rauisuchia 

RauisuchidaePostosuchus kirkpatricki flipped.jpg

PrestosuchidaePrestosuchus-chiniquensis (2).jpg

 "Group X" 

ArizonasaurusArizonasaurus BW white background.jpg

LotosaurusLotosaurus BW white background.jpg

 "Group Y" or Shuvosaurinae 

Sillosuchus

ShuvosaurusShuvosaurus BW flipped.jpg

EffigiaEffigia BW white background.jpg

Cladogram after Brusatte, Benton, Desojo and Langer (2010) [10]

Archosauriformes 

ErythrosuchusErythrosuchus africanus.jpg

EuparkeriaEuparkeria white background.png

ProterochampsidaePseudochampsa life restoration white background.jpg

 Archosauria 

to AvemetatarsaliaMeyers grosses Konversations-Lexikon - ein Nachschlagewerk des allgemeinen Wissens (1908) (Antwerpener Breiftaube).jpg

Crurotarsi 

PhytosauriaSmilosuchus adamanensis flipped.jpg

 Suchia 

AetosauriaDesmatosuchus spurensis flipped.jpg

 Paracrocodylomorpha 

GracilisuchusGracilisuchus BW white background.jpg

 Bathyotica 

ErpetosuchusErpetosuchus BW white background.jpg

CrocodylomorphaDescription des reptiles nouveaux, ou, Imparfaitement connus de la collection du Muséum d'histoire naturelle et remarques sur la classification et les caractères des reptiles (1852) (Crocodylus moreletii).jpg

Revueltosaurus

OrnithosuchidaeOrnithosuchus BW white background.jpg

 Rauisuchia 
 †Rauisuchoidea 

Arganasuchus

Fasolasuchus

Stagonosuchus

TicinosuchusTicinosuchus BW white background.jpg

 Prestosuchidae 

SaurosuchusSaurosuchus BW white background.jpg

Batrachotomus

PrestosuchusPrestosuchus-chiniquensis (2).jpg

 Rauisuchidae 

Tikisuchus

Rauisuchus

PostosuchusPostosuchus kirkpatricki flipped.jpg

Teratosaurus

 †Poposauroidea 

Yarasuchus

Qianosuchus

ArizonasaurusArizonasaurus BW white background.jpg

Bromsgroveia

LotosaurusLotosaurus BW white background.jpg

PoposaurusPoposaurus gracilis (1) flipped.jpg

Sillosuchus

 Shuvosauridae 

ShuvosaurusShuvosaurus BW flipped.jpg

EffigiaEffigia BW white background.jpg

References[edit]

  1. ^ a b c d Nesbitt, S.J. (2011). "The early evolution of archosaurs: relationships and the origin of major clades" (PDF). Bulletin of the American Museum of Natural History. 352: 1–292. doi:10.1206/352.1.
  2. ^ a b c Sereno, P.C.; Arcucci, A.B. (1990). "The monophyly of crurotarsal archosaurs and the origin of bird and crocodile ankle joints". Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 180: 21–52.
  3. ^ Sereno, Paul (1991). "Basal archosaurs: phylogenetic relationships and functional implications". Journal of Vertebrate Paleontology. 11 (Suppl. 4): 1–51. doi:10.1080/02724634.1991.10011426.
  4. ^ Gauthier, J. A.; Nesbitt, S. J.; Schachner, E. R.; Bever, G. S.; Joyce, W. G. (2011). "The bipedal stem-crocodilian Poposaurus gracilis: inferring function in fossils and innovation in archosaur locomotion". Bulletin of the Peabody Museum of Natural History. 52: 107–126. doi:10.3374/014.052.0102.
  5. ^ Gauthier, J.A.; Padian, K. (1985). "Phylogenetic, functional, and aerodynamic analyses of the origin of birds and their flight". In Hecht, M.K.; Ostrom, J.H.; Viohl, G.; Wellnhofer, P. The Beginnings of Birds. Eichstatt: Freunde des Jura-Museums. pp. 185–197.
  6. ^ Benton, M.J.; Clark, J.M. (1988). "Archosaur phylogeny and the relationships of the Crocodylia". In Benton, M.J. Phylogeny and Classification of the Tetrapods. 1. Oxford: Clarendon Press. pp. 295–338.
  7. ^ Brochu, C.A. (1997). "Synonymy, redundancy, and the name of the crocodile stem-group". Journal of Vertebrate Paleontology. 17 (2): 448–449. doi:10.1080/02724634.1997.10010992.
  8. ^ Nesbitt, SJ; Norell, MA. (2006). "Extreme convergence in the body plans of an early suchian (Archosauria) and ornithomimid dinosaurs (Theropoda)". Proceedings of the Royal Society of London B: Biological Sciences. 273 (1590): 1045–1048. doi:10.1098/rspb.2005.3426. PMC 1560254. PMID 16600879.
  9. ^ Nesbitt, S. (2007). "The anatomy of Effigia okeeffeae (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa" (PDF). Bulletin of the American Museum of Natural History. 302: 84. doi:10.1206/0003-0090(2007)302[1:taoeoa]2.0.co;2.
  10. ^ Brusatte, Stephen L.; Benton, Michael J.; Desojo, Julia B.; Langer, Max C. (2010). "The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida)". Journal of Systematic Palaeontology. 8 (1): 3–47. doi:10.1080/14772010903537732.

External links[edit]