Crurotarsi
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| Crurotarsans Fossil range: Triassic - Recent |
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 Gracilisuchus, an early suchian
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The Crurotarsi ("cross-ankles") are a group of archosaurs, whose name was erected as a node-based clade by Paul Sereno in 1991 to supplant the old term Pseudosuchia. Crurotarsi are by definition the sister group of the Avemetatarsalia (all forms closer to birds than crocodiles).
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[edit] Description
The Crurotarsi are one of the two primary daughter clades of the Archosauria. The skull is often massively built, especially in contrast to ornithodires; the snout narrow and sometimes tending to be elongate, the neck is short and strong, and the limb posture ranging from typically reptilian sprawling to dinosaur or mammal-like erect (although this is achieved in a different way to dinosaurs and mammals). The body is often protected by two or more rows of armoured plates. Many forms reached large size: three meters or more in length.
[edit] Evolution
Crurotarsans appeared during the late Olenekian (early Triassic); by the Ladinian (late Middle Triassic) they dominated the terrestrial carnivore niches. Their heyday was the Late Triassic, during which time their ranks included erect-limbed rauisuchians, the crocodile-like phytosaurs, herbivorous armoured aetosaurs, the large predatory poposaurs, the small agile crocodilians Sphenosuchia, and a few other assorted groups.
At the end Triassic extinction, all of the large crurotarsans died out, allowing the dinosaurs to succeed them as the dominant terrestrial carnivores and herbivores. Only the Sphenosuchia and the Protosuchia (Crocodylomorpha) survived.
As the Mesozoic progressed, the Protosuchia gave rise to more typically crocodile-like forms, while dinosaurs were the dominant animals on land, the crocodiles flourished in rivers, swamps, and the oceans; with far greater diversity than they have today.
With the end Cretaceous extinction the ornithodiran dinosaurs became extinct, with the exception of the birds, while the crurotarsan crocodylians continued with little change.
Today, the crocodiles, alligators, and gavials continue as the surviving representatives of this ancient and successful lineage.
[edit] Phylogeny
Cladogram after Parrish (1993), Nesbitt (2003 & 2005), and Nesbitt & Norell (2006).[1]
Crurotarsi |-?Doswellia |-?Tarjadia |-?Parringtonia |-?Ctenosauriscidae `--Crocodylotarsi |--Phytosauria `--Suchia |--Prestosuchidae |-?Turfanosuchus `--Rauisuchiformes |-?Revueltosaurus |--Aetosauria `--Rauisuchia |--Rauisuchidae `--Paracrocodylomorpha |--Gracilisuchus |--Poposauridae `--Bathyotica |--Erpetosuchus `--Crocodylomorpha
[edit] See also
[edit] References
- Benton, M. J. (2004, 3rd ed.). Vertebrate Paleontology. Blackwell Science.
- Sereno, Paul (1991). "Basal archosaurs: phylogenetic relationships and functional implications". Journal of Vertebrate Paleontology (Suppl.) 11: pp. 1-51.
[edit] External links
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