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.
- Pol, Diego & Rauhut, Oliver. 2012. A Middle Jurassic abelisaurid from Patagonia and the early diversification of theropod dinosaurs. Proceedings of the Royal Society B: Biological Sciences.