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Diapsida : Archosauromorpha : Archosauriformes : Archosauria


Postosuchus kirkpatricki
A cast of the reconstructed skull of Postosuchus kirkpatricki, a Late Triassic poposaurid rauisuchian from Apache County, AZ.
Archosauria is defined as the most recent common ancestor of birds and crocodiles and all of its descendants. By definition then, Archosauria consists of two big clades that are sister taxa (i.e., closest relatives) of each other: the croc-line archosaurs, or pseudosuchians, and the bird-line archosaurs, or ornithosuchians. Ornithosuchia includes a lot of animals that are very different from birds, including pterosaurs, huge sauropods like Brachiosaurus, and bizarre plant-eating dinosaurs like Stegosaurus and Triceratops. Similarly, most pseudosuchians were not very similar to living crocs. In a paper on spinosaurs, Tom Holtz pointed out that the evolution of theropod dinosaurs was more than just a "bird factory" (Holtz 19981). Likewise, the evolution of pseudosuchians was more than just a croc factory.

Pseudosuchia includes these fairly distinct groups:

Crocodylomorpha phylogeny

Text by Matt Wedel, 5/2007; Postosuchus photo by Dave Smith, UCMP
1Holtz, T.R., Jr. 1998. Spinosaurs as crocodile mimics. Science 282(5392):1276-1277. DOI: 10.1126/science.282.5392.1276