Ornithischians with well known anatomical adaptations include the ceratopsians or "horn-faced" dinosaurs (e.g. "Triceratops"), armored dinosaurs (Thyreophora) such as stegosaurs and ankylosaurs, pachycephalosaurs and the ornithopods. There is strong evidence that certain groups of ornithischians lived in herds, often segregated by age group, with juveniles forming their own flocks separate from adults. Some were at least partially covered in filamentous (hair- or feather- like) pelts, and there is much debate over whether these filaments found in specimens of "Tianyulong", "Psittacosaurus", and "Kulindadromeus" may have been primitive feathers.