Psittacosaurus
All species of Psittacosaurus were gazelle-sized bipedal herbivores with a high, powerful beak on the upper jaw. At least one species had long, quill-like structures on its tail and lower back, possibly with a display function. Psittacosaurs were early ceratopsians. They developed  adaptations of their own, but they also shared features with later ceratopsians, such as Protoceratops and the elephant-sized Triceratops.