Sauropodomorpha
Saturnalia
Prosauropoda
Sauropoda
Theropoda
Eoraptor
Herrerasauridae
Ceratosauria
Tetanurae
Saurischians (from the Greek Saurischia meaning "lizard hip") are one of the two orders/branches of dinosaurs. They are distinguished from the Ornithischians by retaining the ancestral configuration of bones in the hip. All carnivorous dinosaurs, the theropods) are members of the Saurischians, as well as one of the two great lineages of herbivorous dinosaurs, the sauropodomorphs. At the end of the Cretaceous, and all non-avian Saurischians became extinct during the Cretaceous-Tertiary extinction event.
The Saurischians were differentiated from the Ornithischians in the Late Triassic. The Ornithischians evolved a new hip structure, with the pubis rotating to become parallel with the ischium . This hip structure is similar to that of birds, and so Ornithischians are termed "bird-hipped" dinosaurs, while the Saurischians are "lizard-hipped". Ironically, the true bird-hip possessed by modern birds evolved from the lizard-hipped theropods in the Jurassic, in an example of convergent evolution.
Harry Seeley split all dinosaurs into two great orders based on their hip structure in 1888. While this has stood the test of time, there is a minority theory, first popularized by Robert Bakker in The Dinosaur Heresies that separates the theropods into their own group and places the two great groups of herbivorous dinosaurs, the sauropodomorphs and ornithischians, together in a separate group named as the Phytodinosauria ("plant dinosaurs") (Bakker), or Ornithischiformes (Cooper).
