An international research team, led by Dr Maria McNamara from the University of Bristol’s School of Earth Sciences, has shown that the original colour of fossil feathers may have been tainted by the extreme geological processes deep below the earth’s surface.

The results, published in the journal Biology Letters today [27 March], suggest that previous reconstructions may be flawed.

The analysis focuses on melanosomes – colour-bearing organelles which are buried within the structure of feathers and hair in birds and mammals. They give black, grey, and rufous tones such as orange and brown.

Because melanosomes are an integral part of the tough protein structure of the feather, they survive when a feather survives, even for hundreds of millions of years.

Dr McNamara, who led a team from Yale University and University College Dublin, said: “The problem was that we had no idea whether melanosomes could survive the fossilisation process intact. Our experiments show that this is not the case and that the geometry of the melanosimes changed. The results cast a cautionary light on studies of fossil feather colour and suggest that some previous reconstructions of the original plumage colours of fossils may not be accurate.”

Using a novel experimental technique pioneered in the group’s recent study on the colours of fossil insects, the team looked at feathers of different colours and from different species. The geometry of the melanosomes in all feathers changed during the experiments.

Co-author Professor Derek Briggs, from Yale University, said: “This study will lead to better interpretations of the original plumage colours of diverse feathered dinosaurs and fossil birds. Fossils that have experienced relatively mild burial conditions will yield the most accurate reconstructions.”

Co-author Dr Patrick Orr, from University College Dublin, says that the experimental technique used by the team is going from strength to strength. He added: “This approach can be used to investigate broad questions relating to the fossilisation process and we have several new projects in the pipeline.”

The research was carried out at Yale University and was supported by a Marie Curie International Mobility Fellowship through University College Dublin and the National Science Foundation, awarded to Dr McNamara.