(Optical and false-colored photo of 120 million year old bird fossil. From "Trace Metals as Biomarkers for Eumelanin Pigment in the Fossil Record" by Wogelius et al. in Science Express)
Prehistoric birds in book illustrations come in all different colors: flashy blues, bright reds, and neon greens. But were the birds really those colors? Well, Confuciusornis sanctus, one the oldest fossilized birds, wasn't. Instead, most of its feathers were dark brown or black, found a team of international scientists using a new x-ray technique. That doesn’t mean that other birds long extinct weren’t vibrant colors, but now scientists can put some pigment puzzles to rest.
Getting the colors correct isn’t only important for illustrators, though. The color of bird plumage from millions of years ago can give scientists clues about how those birds lived: how they communicated, if they utilized camouflage, if coloring was a way to attract a mate. The results published June 30 in Science Express are some of the first to give us a glimpse at what birds looked like while they were sharing space with dinosaurs, their evolutionary relatives.
Most of the color in feathers comes from pigments, such as the melanins that also give human skin its tone. The scientists found that one of these pigments, eumelanin, which makes a dark brown or black, is found in the same places where the metal ion copper concentrates. Unlike organic material, metals don’t degrade, so the team used very powerful x-rays to scan the fossils of extinct birds for copper at the Department of Energy's SLAC National Accelerator Laboratory. Scanning the fossils allowed the scientists to put together a map of where the copper was located and, therefore, where the dark pigment was, too.
One of the fossils they scanned was Confuciusornis sanctus, a bird about 120 million years old and the oldest known to have a beak. The scientists false-colored the pictures, so that copper is red, calcium is blue (which is why the bird's bones above are blue), and zinc is green. Copper was concentrated heavily where the body feathers would be and somewhat concentrated in the wing feathers. The scientists also analyzed two feathers found at the Green River fossil deposit using the same technique to see if the copper and pigment pattern was true of other species as well. The feathers showed that the areas that had higher concentrations of copper were indeed darker.
The results: C. sanctus’ downy body feathers were a dark color, while its wings were lighter, except at the tips. Despite the beautiful scan pictures, for now, no rainbow birds.
(C. sanctus drawing. From "Trace Metals as Biomarkers for Eumelanin Pigment in the Fossil Record" by Wogelius et al. in Science Express)
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Skeletons in the Deposit: Looking at the connections between dinos and birds