saurischians

Saurischia, meaning “lizard-hipped,” is one of the two principal divisions of dinosaurs, the other being Ornithischia. The name refers to the orientation of the pelvis, with the pubis bone pointing forward in saurischians. This group includes two major lineages: Theropoda, which were primarily bipedal carnivores and include many well-known dinosaurs, and Sauropodomorpha, which began with smaller, long-necked forms and later evolved into the giant sauropods such as Brachiosaurus and Diplodocus. Birds are living descendants of theropod dinosaurs, making them part of the saurischian lineage.

Theropods were the dominant terrestrial carnivores in many ecosystems and exhibit a wide range of sizes and forms, from small, agile predators to large apex predators. Sauropodomorphs started as relatively small, bipedal herbivores in the Triassic and later evolved into the enormous, long-necked sauropods that characterized much of the Jurassic and Cretaceous. The shared saurischian pelvis is a key structural feature, but the two subgroups diverged early and followed distinct evolutionary paths.

Saurischians first appear in the fossil record in the Late Triassic, and their various lineages persisted until the end of the Cretaceous, when non-avian dinosaurs disappeared. The most enduring saurischian lineage is Theropoda, whose evolutionary path led to birds in the Late Jurassic to Early Cretaceous. In modern taxonomy, birds are considered a living dinosaur lineage within Theropoda, within Saurischia, illustrating the deep evolutionary connections within this group.