The only small ornithischian skin reported was a nonscaly, punctured surface on Thescelosaurus earlier in this century, but the integument was not figured and is not accessible. The combined data suggests but does not prove that feathers evolved in terrestrial theropods well before the evolution of birds, at least by the L. Jurassic and in tetanuran theropods. How much earlier feathers may have evolved is not clear, so Triassic and earlier Jurassic theropods may or may not have been insulated. Therefore artists should feel free to restore Coelophysis with or without feathers. If someone tries to tell you otherwise just subtly roll your eyes, or smile enigmatically yet knowingly - its what I used to do.
Feathers are highly probable in the advanced bird-like theropods.
What small ornithischians were wearing is up for grabs. The probable presence of feathers in at least some small theropods has important metabolic and thermoregulatory implications. Recently it has been asserted that the presence of feathers does not necessarily indicate endothermy, contrary to a long opinion otherwise. This is false because some modern flying birds have flight muscles much smaller than the avian norm, and early bird arms and shoulder girdles were large enough to support them. Another argument is that early bird bones show they grew slowly like reptiles.