1. Herbivorous Diet: Ornithischians were exclusively herbivorous dinosaurs. They possessed specialized teeth and jaws that were adapted for processing plant material. Some Ornithischians had broad, leaf-shaped teeth for browsing on vegetation, while others had more specialized beaks or sharp teeth for consuming specific plant parts.
2. Predominantly Bipedal: Most Ornithischians were bipedal, meaning they walked on their two hind legs. This upright posture allowed them to reach and browse on higher vegetation. However, some Ornithischians, such as the quadrupedal Stegosaurus, were exceptions to this general rule.
3. Pelvic Structure: Ornithischians are named for their unique pelvic structure, which is referred to as the "ornithischian pelvis." This pelvic arrangement is characterized by the presence of three bones: the ilium, the pubis, and the ischium. The ilium and pubis extend forward, while the ischium points backward, forming a triangular shape.
4. Specialized Beaks: Some Ornithischians, such as the duck-billed Hadrosaurs, developed specialized beaks for feeding. These beaks were formed by the modification of premaxillary and maxillary bones, allowing the dinosaurs to efficiently graze and strip leaves from plants.
5. Cheek Teeth: Many Ornithischians had cheek teeth, also known as dental batteries, that helped them grind and process plant material. These teeth were arranged in multiple rows and constantly replaced as they wore down, ensuring efficient feeding.
6. Varied Body Forms: Ornithischians exhibited a wide range of body forms and adaptations. They included small, agile dinosaurs like Hypsilophodonts, heavily armored Ankylosaurs, massive Stegosaurians with distinctive plates on their backs, and the large, duck-billed Hadrosaurs.
7. Predominant Mesozoic Distribution: Ornithischians flourished during the Mesozoic Era, which includes the Triassic, Jurassic, and Cretaceous periods. They were a diverse group and occupied various habitats worldwide, contributing to the rich diversity of dinosaur life during that time.
8. Absence of Postacetabular Fenestrae: Unlike Saurischian dinosaurs, Ornithischians lack postacetabular fenestrae. These are openings or gaps in the hip bones (pelvis) behind the hip joint. This absence further distinguishes Ornithischians from their dinosaurian counterparts.