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Which dinosaur groups belonged to the ornithischians?

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Illustration showing various dinosaur species drawn to scale and grouped by geologic era: Late Cretaceous, Early Cretaceous, Jurassic, and Triassic. Dinosaurs range from large species like Brachiosaurus and Tyrannosaurus to smaller ones like Velociraptor and Compsognathus, with a human silhouette included for size comparison. Measurement bars at the bottom indicate 1 meter and 3 feet for scale reference. — dinosaur A selection of dinosaurs grouped by the geologic interval in which they lived.

Ornithischians, commonly known as "bird-hipped" dinosaurs, are one of the two primary lineages of dinosaurs, the other being the saurischians. Despite their name, they are not the ancestors of modern birds.12

Ornithischians are divided into two major subgroups:

Cerapoda: This group is further subdivided into the Ornithopoda, Pachycephalosauria, and Ceratopsia. Some researchers group the Pachycephalosauria and Ceratopsia together as Marginocephalia.1
Thyreophora: This group consists of the Stegosauria and Ankylosauria and their relatives.1

These herbivorous dinosaurs are characterized by a unique pelvic structure where the pubic bone points backward, as well as the presence of a predentary bone in the lower jaw. While basal forms like Lesothosaurus existed, these two main lineages represent the primary classification of the group.13