Ceratosaurs are members of a group of theropod dinosaurs defined as all theropods sharing a more recent common ancestry with Ceratosaurus than with birds. There is no agreed upon listing of species or diagnostic characters of Ceratosauria, though they were less derived anatomically than the more diverse Tetanurae. According to the latest and most accepted theory, Ceratosauria includes the Late Jurassic to Late Cretaceous theropods Ceratosaurus, Elaphrosaurus, and Abelisaurus, found primarily (though not exclusively) in the Southern Hemisphere. Originally, Ceratosauria included the above dinosaurs plus the Late Triassic to Early Jurassic Coelophysoidea and Dilophosauridae, implying a much earlier divergence of ceratosaurs from other theropods. However, most recent studies have shown that coelophysoids and dilophosaurids do not form a natural group with other ceratosaurs, and are excluded from this group.