Ceratosaurs are a group of theropod dinosaurs. They are defined as "all theropods sharing a more recent common ancestry with Ceratosaurus than with birds".
Temporal range: Jurassic–Cretaceous
Ceratosauria includes the Upper Jurassic to Upper Cretaceous theropods Ceratosaurus, Elaphrosaurus, and Abelisaurus, found mainly in the southern hemisphere.
The earlies known Ceratosaur is from the Middle Jurassic of Patagonia, Eoabelisaurus. This predates the oldest certainly known known member of the lineage by more than 40 million years. The almost complete skeleton of Eoabelisaurus shows the earliest evolutionary stages of the distinctive abelisaurid modification of the forelimb.
Originally, Ceratosauria included the above dinosaurs plus the Upper Triassic to Lower Jurassic Coelophysis and Dilophosaurus. This implied a much earlier divergence of ceratosaurs from other theropods. However, recent studies have shown that coelophysoids and dilophosaurids do not form a natural group with other ceratosaurs, and so they are excluded from this group.