The colours of a bird that lived 120 million years ago have been revealed from trace remains of pigments on its fossil, and the same technique may be used to reveal the colours of dinosaurs.
The research, published Thursday online in Science Express suggests that Confuciusornis sanctus, the earliest beaked bird ever discovered, had darker areas on its downy body feathers and its long tail feathers.
It is the first chemical evidence of animal pigments in the fossil record, said Phil Manning, a paleontologist at the University of Manchester and a co-author of the study, in a video interview with Science.
"And these pigments are over 120 million years old."
The research team from the U.S., the U.K. and China scanned fossils of Confuciusornis sanctus using an X-ray beam from a synchrotron at Stanford University. They also scanned the fossil feather of a grebe-like bird called Gansus yumenensis that lived about 110 million years ago and is considered the oldest modern bird.
Different chemical elements absorb different colours of X-ray light, and the colours of the X-ray beam allowed the researchers to see which elements, such as copper or calcium, were in which parts of the fossil.
Copper is found in eumelanin, the pigment found in brown eyes or black hair in humans, and dark-coloured eyes, feathers, skin or fur in other animals. So the researchers looked for copper on the fossil.
A synchrotron is a ring-shaped particle accelerator that speeds up electrons close to the speed of light using powerful electromagnets and radio frequency waves. That produces brilliant, highly focused light from which researchers can separate out very specific colours, including infrared, ultraviolet and x-ray beams.
Uwe Bergmann of the SLAC National Accelerator Laboratory in California said the technique used in the fossil study requires 5 to 10 million measurements. Those take less than 12 hours with the intense synchrotron beam. "It would probably take 1,000 times longer with a commercial X-ray tube," he said.
For the technique used to analyze the type of copper in the pigments, a single colour of X-rays with a very small focus is needed — something available only from a synchrotron.
Canada has a synchrotron facility at the University of Saskatchewan called the Canadian Light Source.
They found it on Confuciusornis sanctus's body and its tail feathers.
A different kind of X-ray data can reveal not only the kind of element, but what an average atom of that element was attached to. For example, the data for copper atoms would look slightly different if they were all attached to an organic, biological molecule such as eumelanin than if they were attached to oxygen and formed an inorganic oxide.
Co-author Sam Webb, a staff scientist at the synchrotron facility at Stanford, examined the feather of Gansus yumenensis using the other X-ray technique. He found that the copper in the feather looked as if it had been part of eumelanin pigment molecules.
"Most other compounds that contain copper in the body, or for that matter in the fossil matrix, would have a different spectroscopic signature," said Uwe Bergmann, another co-author of the paper. Bergmann is director of the Linac Coherent Light Source at the SLAC National Accelerator in Menlo Park, Calif.
The researchers compared their results with X-ray scans of feathers from modern birds, and confirmed that darker parts of the feather had similar patterns of copper to those they found in the fossil.
Webb said one of the advantages of the technique is that it doesn't damage the fossil, which can still be displayed at a museum after scanning.
Manchester University scientist Roy Wogelius, the lead author of the paper, said in a video interview with Science that he hopes to be able to use the same technique to detect other pigments.
Bergmann added, "We think this might be possible, but we don't know yet."
But James Gurney, author and illustrator of the best-selling Dinotopia series, which features a world where dinosaurs and humans live together was already speculating about the possibilities.
"These new techniques for teasing out evidence of pigrmentation will take a lot of the guesswork out of reconstructing the appearance of extinct dinosaurs and birds," he said in a statement.