saurischia

Saurischia is a clade of dinosaurs defined by the structure of the pelvis, commonly described as lizard-hipped in contrast to the bird-hipped pelvis of the other major dinosaur group. The name derives from Greek roots meaning lizard hip. First named by Seeley in 1888, Saurischia includes two principal lineages: Theropoda and Sauropodomorpha. Together with Ornithischia, Saurischia forms the traditional classification of dinosaurs.

The two major subgroups within Saurischia are Theropoda and Sauropodomorpha. Theropods were predominantly bipedal carnivores, though some groups evolved omnivory or herbivory, and they include numerous well-known genera such as Tyrannosaurus, Velociraptor, and Allosaurus. Birds are their most famous modern descendants, representing a living lineage of theropod saurischians. Sauropodomorpha began as small, often bipedal herbivores and later gave rise to the enormous sauropods, such as Brachiosaurus, Diplodocus, and Patagotitan. Early sauropodomorphs like Plateosaurus illustrate the transition toward the highly elongated necks and massive bodies characteristic of later members.

In appearance and locomotion, saurischians are distinguished from ornithischians by their hip arrangement, with the pubis generally directed forward in saurischians. The group first arose in the Late Triassic, with a fossil record that spans many ecosystems across Pangaea. Saurischia remains a foundational clade in dinosaur phylogeny, illustrating a major split in early dinosaur evolution and encompassing the lineages that would dominate for much of the Mesozoic era and the ancestors of modern birds.