Ornithischian dinosaurs were a diverse group of herbivorous dinosaurs that existed during the Mesozoic era. These dinosaurs were known for their bird-like hips, which set them apart from other groups of dinosaurs. Synonyms for the term ornithischian dinosaur include bird-hipped dinosaur, avian-hipped dinosaur, and ornithopod dinosaur. Other species within this group include stegosaurs, ankylosaurs, and ceratopsians, which are characterized by their heavily armored body and horned faces. The ornithischian dinosaurs were an important part of the ecosystem during their time on earth and have left behind a rich fossil record that continues to shed light on their biology and evolution.