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Early Triassic–Present, 250–0Ma
|Crocodiles basking in the sun. Crocodiles can move quite fast on land by tucking their legs under their body: an archosaur feature.|
Arctopoda Haeckel, 1895
Archosaurs are a large group of reptiles, including all crocodiles, birds, dinosaurs, and pterosaurs (flying reptiles). There are also a number of smaller extinct groups, mostly from the Triassic period.
- Teeth set in sockets, which makes them less likely to be torn loose during feeding. Some archosaurs, such as birds, are secondarily toothless.
- Opening in the skull in front of the eyes but behind the nostrils, reduces the weight of the skull.
- Small openings in the jaw bones, which reduces the weight of the jaw slightly.
- Legs held under the body rather than sprawled. This improves both breathing and movement.
The archosaurs or their immediate ancestors survived the catastrophic Permian–Triassic extinction event. Then, in the early and middle Triassic, there was rapid evolution into the types of aquatic and land tetrapods which dominated the rest of the Mesozoic era.
- Crurotarsi or Pseudosuchia: The crocodile line of crown-group Archosauria
- Benton M.J. 2004. Vertebrate paleontology. 3rd ed, Blackwell, Oxford.
- Carroll R.L. 1988. Vertebrate paleontology and evolution. Freeman N.Y.
- Benton M. 1990. The reign of the reptiles. Crescent, N.Y.
- Brusatte, Stephen L. et al 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida). Journal of Systematic Palaeontology. 8: 1, 3–47. 
- 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.