Saurischians are a group of dinosaurs characterized by their lizard-like hip structure. This group is divided into two main subcategories: Theropoda, which includes carnivorous dinosaurs like Tyrannosaurus rex, and Sauropodomorpha, which consists of large, long-necked herbivores like Brachiosaurus. These dinosaurs lived during the Mesozoic Era, which spanned from about 252 to 66 million years ago. Saurischians were diverse in size and shape, adapting to various environments. Their unique skeletal features distinguish them from the other major dinosaur group, the Ornithischians, which have a different hip structure.