Leaellynasaura

A little creature from the Cretaceous period. It seems to be possible that fuzz occurred wider in smaller ornithischians, such like that.
UPDATE: Now, after Kulindadromeus (as well as Tianyulong) discovery we know, that some little ornithischians had some sort of fuzz. They weren't necessarily feathers, but may be homologous with feathers (maybe interesting case of deep homology) and functioned as a thermal isolation.