Ornithischia (from the Greek ornitheos meaning "of a bird" and ischion meaning "hip joint") is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure similar to that of birds. It is one of the two basic divisions of dinosaurs (the other being Saurischia). Birds are members of the Saurischia, or "lizard-hipped" dinosaurs. Ornithischia is well-supported as one of the two major groups in the Dinosauria. Many characteristics define the group though most are thought to be linked to herbivory.