Sphenosuchia

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Sphenosuchians
Temporal range: Late Triassic - Late Jurassic, 228–150Ma
Hesperosuchus BW.jpg
Life restoration of Hesperosuchus agilis
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Crocodylomorpha
Informal group: Sphenosuchia
von Huene, 1942
Genera

See below

Synonyms
  • Pedeticosauria Walker, 1968

Sphenosuchia is a suborder of basal crocodylomorphs that first appeared in the Triassic and occurred into the Late Jurassic. Most were small, gracile animals with an erect limb posture. They are now thought to be ancestral to crocodyliforms, which include all living crocodilians.

Stratigraphic range[edit]

The earliest known members of the group (i.e. Hesperosuchus) are early Norian in age, found in the Blue Mesa Member of the Chinle Formation. Only one sphenosuchian is currently known from the Middle Jurassic, Junggarsuchus, from the Junggar Basin (Shishugou Formation) of China during either the Bathonian or the Callovian (~165 Ma) in age.[1] The youngest sphenosuchian, Macelognathus, is known from the Late Jurassic of North America during the Kimmeridgian, (155 - 150 Ma).

Phylogeny[edit]

The monophyly of the group is debated, although several synapomorphies characterize the clade, including extremely slender limbs, a compact carpus and an elongate coracoid process.

In 2002, Clark and Sues found a possible sphenosuchian clade of Dibothrosuchus, Sphenosuchus, and possibly Hesperosuchus and Saltoposuchus, with several other genera in unresolved positions (Kayentasuchus, Litargosuchus, Pseudhesperosuchus, and Terrestrisuchus).[2] More recently, however, Clark et al. (2004) argued for the paraphyly of the group, contending that morphological characters were secondarily lost in more highly derived crocodylomorphs.[1] Further analysis and study is required before the group's monophyly is resolved with certainty — a perfect phylogenetic analysis is, at present, impossible due to a paucity of fossil remains demonstrating phylogenetically informative characters.

Below is a cladogram modified from Nesbitt (2011).[3] Sphenosuchians are marked by the green bracket.

Crocodylomorpha 

 CM 73372




 Hesperosuchus 



 Dromicosuchus 




 Sphenosuchus 




 Dibothrosuchus 



 Terrestrisuchus 




 Litargosuchus 




 Kayentasuchus 


 Crocodyliformes 

 Orthosuchus



 Protosuchus



 Alligator









Sphenosuchians

Genera[edit]

Genus Status Age Location Unit Notes Images
Valid Late Triassic  Brazil Santa Maria Formation A putative sphenosuchid;[4] alternatively, it could be a rauisuchian.[5]
Valid Early Jurassic  China Lower Lufeng Series Dibothrosuchus BW.jpg
Valid Late Triassic  USA Newark Supergroup
Valid Late Triassic (Carnian)  Germany Schilfsandstein Formation A possible sphenosuchian;[6] alternatively, it could be an erpetosuchid.[7] Dyoplax holotype.jpg
Valid Late Jurassic  USA Morrison Formation Possible synonym of Macelognathus Hallopus victor.jpg
Valid Late Triassic (Carnian)  USA Chinle Formation
Valid Middle Jurassic  China Shishugou Formation Junggarsuchus sloani.jpg
Valid Early Jurassic (Sinemurian - Pliensbachian)  USA Kayenta Formation
Valid Early Jurassic  South Africa Elliot Formation Litargosuchus leptorhynchus.jpg
Valid Late Jurassic  USA Morrison Formation Macelognathus.jpg
Nomen dubium Late Triassic  USA Dockum Group An indeterminate sphenosuchian known only from undiagnostic vertebrae[8]
Valid Early Jurassic  China Lower Lufeng Series
Valid Late Triassic (Norian)  Argentina Los Colorados Formation
Valid Late Triassic  USA Redonda Formation
Valid Late Triassic (Norian)  Germany

  Switzerland  UK

Löwenstein Formation

Trossingen Formation Lossiemouth Sandstone

Saltoposuchus BW.jpg
Valid Early Jurassic  South Africa Elliot Formation
Valid. Late Triassic  UK Terrestrisuchus BW.jpg
Valid Late Triassic  Argentina Ischigualasto Formation Known specimens may represent basal crocodylomorphs and dinosaurs[8]

References[edit]

  1. ^ a b Clark, J.M., et al. (2004).A Middle Jurassic 'sphenosuchian' from China and the origin of the crocodylian skull Nature 430:1021-1024.
  2. ^ Clark, J.M., and Sues, H.-D. (2002). Two new species of basal crocodylomorphs and the status of the Sphenosuchia. Zoological Journal of the Linnean Society 136:77−96.
  3. ^ Nesbitt, S.J. (2011). "The early evolution of archosaurs: relationships and the origin of major clades". Bulletin of the American Museum of Natural History 352: 1–292. doi:10.1206/352.1. 
  4. ^ Mattar, L.C.B. 1987. Descrição osteólogica do crânio e segunda vértebrata cervical de Barberenasuchus brasiliensis Mattar, 1987 (Reptilia, Thecodontia) do Mesotriássico do Rio Grande do Sul, Brasil. Anais, Academia Brasileira de Ciências, 61: 319–333.
  5. ^ Kischlat, E.-E. (2000). "Tecodôncios: a aurora dos arcossáurios no Triássico". In Holz, M.; and De Ros, L.F. (eds.). Paleontologia do Rio Grande do Sul. Porto Alegre: CIGO/UFRGS. pp. 273–316. 
  6. ^ a b Lucas, S. G.; Wild, R.; and Hunt, A. P. (1998). "Dyoplax O. Fraas, a Triassic sphenosuchian from Germany". Stuttgarter Beiträge zur Naturkunde, B 263: 1–13. 
  7. ^ Michael W. Maisch, Andreas T. Matzke, Thomas Rathgeber (2013). "Re-evaluation of the enigmatic archosaur Dyoplax arenaceus O. Fraas, 1867 from the Schilfsandstein (Stuttgart Formation, lower Carnian, Upper Triassic) of Stuttgart, Germany". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 267 (3): 353–362. doi:10.1127/0077-7749/2013/0317. 
  8. ^ a b Clark, J. M.; Sues, H.-D.; and Berman, D. S. (2001). "A new specimen of Hesperosuchus agilis from the Upper Triassic of New Mexico and the interrelationships of basal crocodylomorph archosaurs". Journal of Vertebrate Paleontology 20 (4): 683–704. doi:10.1671/0272-4634(2000)020[0683:ANSOHA]2.0.CO;2. 
  9. ^ Harris, Jerald D.; Lucas, Spencer G.; Estep, J. W.; and Jianjun Li (2000). "A new and unusual sphenosuchian (Archosauria: Crocodylomorpha) from the Lower Jurassic Lufeng Formation, People's Republic of China". Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 215 (1): 47–68.