Temporal range: Jurassic-Cretaceous
Ceratosauria are dinosaurs first seen in the fossil record in the late Triassic period, some 225 million years ago. Ceratosaurians also had strongly curved S-shaped necks like birds do; this is a trait inherited from a distant archosaurian ancestor. One diagnostic characteristic of most of the Ceratosauria (except for Ceratosaurus, which was an oddball that appeared long after the other ceratosaurs, and may not even belong in this group) is the loose attachment between the premaxilla (the most anterior bone of the upper jaw) and the maxilla (the main upper jaw bone, posterior to the premaxilla). A large tooth from the lower jaw normally fits into the notch formed by this loose attachment. You can see this character clearly on Coelophysis and Dilophosaurus.