The Colour and Preservation of Fossil Feathers

Feathers are characteristic of birds and some theropod dinosaurs. Fossil examples, the great majority carbonaceous, have been described from about 50 localities around the world. A number of studies have demonstrated that the organic material in fossil feathers consists of micron-sized oblate structures, which have been described as feather degrading bacteria. A comparison with modern feathers, however, among other lines of evidence, shows that these structures are the fossilized melanosomes that imparted color to the feather.

A striking feather from the Lower Cretaceous Crato Formation, Brazil, preserves distinct light and dark bands which match isochronic color bands in modern feathers. Oblate structures are only present in the dark bands, where they are aligned along the length of the feather barbs and barbules. These oblate structures are similar in size to the eumelanosomes in extant black feathers and are organized in the same way.

The discovery of eumelanosomes in fossil feathers opens up the possibility of predicting the original coloration of fossil birds and dinosaurs with implications for interpreting their ecology and behaviour. Distinct arrangements of eumelanosomes also give rise to structural colors, including iridescence. Phaemelanosomes, give rise to rusty red and buff yellow colors. they are morphologically distinct from eumelanosomes and their preservation potential remains to be assessed.

Many other melanin bearing structures are preserved in the fossil record such as eyes, squid ink sacs, and insect cuticles. Melanin is very resistant to chemical and bacterial degradation. It may have played a much more important role in the preservation of some organic soft tissues than hitherto realized.