Ornithischians are a group of herbivorous dinosaurs that lived during the Mesozoic Era. They are characterized by their bird-like hips, which is reflected in their name, meaning "bird-hipped." This group includes well-known dinosaurs such as Stegosaurus, Triceratops, and Ankylosaurus. Ornithischians were diverse, ranging from small, bipedal forms to large, quadrupedal species. These dinosaurs thrived in various environments and exhibited a range of adaptations for feeding and defense. Some had armor plating, while others developed elaborate horns or frills. Ornithischians played a significant role in their ecosystems, influencing plant life and serving as prey for large carnivorous dinosaurs like Tyrannosaurus rex.