Sphenosuchia
| Sphenosuchians Temporal range: Late Triassic - Late Jurassic, 228–150 Ma |
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| Life restoration of Hesperosuchus agilis | |
Scientific classification  |
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | Crocodylomorpha |
| informal group: | Sphenosuchia von Huene, 1942 |
| informal group: | Sphenosuchidae Haughton, 1924 |
| Genera | |
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.
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[edit] Stratigraphic range
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).
[edit] Phylogeny
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.
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Sphenosuchians
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[edit] Genera
[edit] References
- ^ 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.
- ^ 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.
- ^ 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. http://digitallibrary.amnh.org/dspace/bitstream/2246/6112/1/B352.pdf.
- ^ 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.
- ^ 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.
- ^ 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.
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