 All carnivorous dinosaurs (certain types of theropods) are traditionally classified as saurischians, as are all of the birds and 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 in the course of the Cretaceous–Paleogene extinction event.Birds, as direct descendants of one group of theropod dinosaurs, are a sub-clade of saurischian dinosaurs in phylogenetic classification.