Dinosaurs belong to the animal family known as Dinosauria. They were a diverse group of reptiles that appeared during the Mesozoic Era, which spanned from approximately 252 million to 66 million years ago. Dinosaurs are characterized by their upright stance, with legs positioned directly beneath their bodies, a feature that distinguished them from other reptiles. They exhibited a wide range of sizes, from small, bird-like dinosaurs to enormous giants like the long-necked sauropods and the fearsome Tyrannosaurus rex. Dinosaurs were incredibly successful and dominant during their time, inhabiting various environments and evolving into numerous species with unique adaptations. The dinosaur family is further classified into two major groups: Saurischia, which includes the theropods (carnivorous dinosaurs) and sauropodomorphs (long-necked herbivores), and Ornithischia, which encompasses herbivorous dinosaurs with bird-like hip structures.