All
feathered dinosaurs known so far are theropods, but not all dinosaurs with hair-or-bristle-like integumentary structures. The dinosaur discussed in the article,
Tianyulong, has hollow, rigid filaments on its neck, back, and tail (it apparently possessed a coat of shorter bristles all over its body as well). This is significant because it belongs to a very "primitive" (I dislike using the word because it implies an evolutionary hierarchy) group of ornithischian dinosaurs, the heterodontosaurs. If its filaments are the product of the ornithischians common ancestry with the saurischians (the group that contains theropods), then this could mean that
all ornithischians had the genetic potential for fuzziness. If it evolved its bristles independently of the theropods, then evidently it isn't too difficult for such structures to develop, and they could have appeared in other ornithischians in the same way. Furthermore, evidence for such integument is present in
Triceratops's own group, the Ceratopsia. One of the most...ahem...primitive ceratopsians,
Psittacosaurus, had a line of quill-like structures along the top of its tail, similar to the filaments on
Tianyulong. And (I completely forgot to mention this in my last post
)
Triceratops itself has apparently been found to have bristle-like structures on its skin. I am unaware of the precise nature of these, and know that there are skin impressions from
Triceratops that show that it had scales as well; I am also, admittedly, doubtful that real
Triceratops would have had Tria-style eyelashes, but the concept is not completely impossible.
