Sphenosuchia
| Sphenosuchia Temporal range:Late Triassic-Late Jurassic,
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| Life restoration ofHesperosuchus agilis | |
Scientific classification
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Clade: | Pseudosuchia |
| Clade: | Crocodylomorpha |
| Informal group: | †Sphenosuchia von Huene,1942 |
| Genera | |
| Synonyms | |
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Sphenosuchiais asuborderofbasalcrocodylomorphsthat first appeared in theTriassicand occurred into theMiddle Jurassic.Most were small, gracile animals with an erect limb posture. They are now thought to be ancestral tocrocodyliforms,a group which includes all livingcrocodilians.
Stratigraphic range
[edit]The earliest known members of the group (i.e.Hesperosuchus) are earlyNorianin age, found in the Blue Mesa Member of theChinle Formation.Only one sphenosuchian is currently known from the Middle Jurassic,Junggarsuchus,from theJunggar Basin(Shishugou Formation) of China during either theBathonianor theCallovian(~165 Ma) age,[1]and theHallopodidaeare known from the Late Jurassic of North America.[2]
Phylogeny
[edit]Themonophylyof the group is debated, although severalsynapomorphiescharacterize the clade, including extremely slender limbs, a compactcarpusand an elongatecoracoid process.
In 2002, Clark and Sues found a possible sphenosuchian clade ofDibothrosuchus,Sphenosuchus,and possiblyHesperosuchusandSaltoposuchus,with several other genera in unresolved positions (Kayentasuchus,Litargosuchus,Pseudhesperosuchus,andTerrestrisuchus).[3]More recently, however, Clarket 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 acladogrammodified from Nesbitt (2011).[4]Sphenosuchians are marked by the green bracket.
Sphenosuchians |
Genera
[edit]| Genus | Status | Age | Location | Unit | Notes | Images |
|---|---|---|---|---|---|---|
| Valid | Early Jurassic |  China
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Lower Lufeng Series | 
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| Valid | Late Triassic |  USA
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Newark Supergroup | |||
| Valid | Late Triassic(Carnian) |  Germany
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Schilfsandstein Formation | A possible sphenosuchian;[5]alternatively, it could be anerpetosuchid.[6] | 
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| Valid | Late Triassic(Carnian) | USA
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Chinle Formation | |||
| Valid | Middle Jurassic | China
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Shishugou Formation | 
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| Valid | Early Jurassic(Sinemurian-Pliensbachian) | USA
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Kayenta Formation | |||
| Valid | Early Jurassic |  South Africa
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Elliot Formation | 
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| Nomen dubium | Late Triassic | USA
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Dockum Group | An indeterminate sphenosuchian known only from undiagnostic vertebrae[7] | ||
| Valid | Early Jurassic | China
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Lower Lufeng Series | |||
| Valid | Late Triassic(Norian) |  Argentina
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Los Colorados Formation | |||
| Valid | Late Triassic | USA
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Redonda Formation | |||
| Valid | Late Triassic(Norian) | Germany
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Löwenstein Formation | 
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| Valid | Early Jurassic | South Africa
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Elliot Formation | |||
| Valid. | Late Triassic |  UK
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| Valid | Late Triassic | Argentina
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Ischigualasto Formation |
References
[edit]- ^abClark, J.M.,et al.(2004).A Middle Jurassic 'sphenosuchian' from China and the origin of the crocodylian skullNature430:1021-1024.
- ^Leardi, Juan Martin; Pol, Diego; Clark, James Matthew (2017-01-19)."Detailed anatomy of the braincase of Macelognathus vagans Marsh, 1884 (Archosauria, Crocodylomorpha) using high resolution tomography and new insights on basal crocodylomorph phylogeny".PeerJ.5:e2801.doi:10.7717/peerj.2801.ISSN2167-8359.PMC5251941.PMID28133565.
- ^Clark, James M.; Sues, Hans-Dieter (2002)."Two new basal crocodylomorph archosaurs from the Lower Jurassic and the monophyly of the Sphenosuchia".Zoological Journal of the Linnean Society.136:77–95.doi:10.1046/j.1096-3642.2002.00026.x.
- ^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.hdl:2246/6112.S2CID83493714.
- ^abLucas, S. G.; Wild, R.; Hunt, A. P. (1998). "DyoplaxO. Fraas, a Triassic sphenosuchian from Germany ".Stuttgarter Beiträge zur Naturkunde, B.263:1–13.
- ^Michael W. Maisch; Andreas T. Matzke; Thomas Rathgeber (2013). "Re-evaluation of the enigmatic archosaurDyoplax arenaceusO. 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.
- ^Clark, J. M.; Sues, H.-D.; Berman, D. S. (2001). "A new specimen ofHesperosuchus agilisfrom 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.S2CID7455338.
- ^Harris, Jerald D.; Lucas, Spencer G.; Estep, J. W.; 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.doi:10.1127/njgpa/215/2000/47.
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