The term "saurischios" refers to one of the two main groups of dinosaurs, characterized by their lizard-like hip structure. This group includes both the carnivorous theropods, like Tyrannosaurus rex, and the herbivorous sauropodomorphs, such as Brachiosaurus. Saurischios are known for their diverse body shapes and sizes, ranging from small, agile predators to massive, long-necked giants. Saurischios first appeared during the late Triassic period and thrived throughout the Jurassic and Cretaceous periods. Their unique adaptations, such as hollow bones and specialized limbs, allowed them to occupy various ecological niches. This group played a significant role in the evolution of modern birds, which are considered descendants of theropod dinosaurs.