Non-avian dinosaurs were uniformly scaly reptiles without feathers.

For most of the history of dinosaur reconstruction, artists had good reason to cover non-avian dinosaurs—that is, dinosaurs other than birds—in reptile-like scales. Fossilized skin impressions showed scales in some species, while feathers were known from birds and the bird-like Archaeopteryx. Without direct evidence, extending feathers broadly across dinosaurs would itself have been speculation.

Exceptional fossils changed the picture. Beginning in the 1990s, deposits in northeastern China preserved fine body coverings around non-avian dinosaur skeletons. Sinosauropteryx was reported with a halo of filamentous structures, and subsequent finds revealed increasingly complex feathers in many theropods. Evidence such as quill knobs on forearm bones showed that feather attachment could sometimes be inferred even when the feathers themselves were not preserved.

The discoveries also weakened the idea that feathers originated solely for powered flight. Filamentous coverings and feathers could serve insulation, display, brooding and other functions before some lineages adapted them for flight.

The old image should not simply be inverted. Many dinosaurs had scales, and some animals combined scales with feathers on different parts of the body. The correction is that uniformly scaly is no longer a defensible description of Dinosauria.