Saurischia (/sɔːˈrɪskiə/ saw-RIS-kee-ə, from the Greek sauros (σαυρος) meaning 'lizard' and ischion (ισχιον) meaning 'hip joint') is one of the two basic divisions of dinosaurs. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure, though today most paleontologists classify Saurischia as an unranked clade rather than an order. Saurischians ('lizard-hipped') are distinguished from the ornithischians ('bird-hipped') by retaining the ancestral configuration of bones in the hip.Sauropod and theropod dinosaurs fall under the class Saurischia. Ornithischia (bird hipped dinosaurs) consists of Ceratopsians and dinosaurs such as Parasaurolophus and Corythosaurus.All carnivorous dinosaurs (the theropods) are saurischians, as are one of the two primary lineages of herbivorous dinosaurs, the sauropodomorphs. At the end of the Cretaceous Period, all saurischians except the birds became extinct. This is referred to as the Cretaceous–Paleogene extinction event. Avians (modern birds), as direct descendants of one group of theropod dinosaurs, are a sub-clade of saurischian dinosaurs in phylogenetic classification.