Sinosauropteryx prima

One of the pieces of evidence to show that birds descended from the theropods is the more or less evolved plumage on the dinosaurs' bodies. The Sihetun site in China has been producing fossils of such a high quality since 1996 that they still show traces of plumage. This is more primitive in the case of Sinosauropteryx: a down formed from simple hollow fibres. The creature could not fly with these but it did keep its body warm.