Pigments of the Past
The research was conducted by an international team working with Phillip Manning, an adjunct professor in the School of Arts and Sciences' Department of Earth and Environmental Science, and Peter Dodson, a professor in both the Department of Earth and Environmental Science and the School of Veterinary Medicine's Department of Animal Biology. They collaborated with Roy Wogelius of the University of Manchester, Uwe Bergmann of Stanford University's SLAC National Accelerator Laboratory and other researchers.
Their work was published in the journal Science on July 1.
Manning and Dodson have long studied fossils of the earliest birds, including Confuciusornis sanctus, which lived 120 million years ago and was one of many evolutionary links between dinosaurs and birds, and Gansus yumenensis, which is considered the oldest modern bird and lived more than 100 million years ago. Their partnership with researchers from Manchester and Stanford, however, has opened a new avenue of investigation.
"Every once in a while we are lucky enough to discover something new, something that nobody has ever seen before," said Wogelius, a geochemist and the paper's lead author.
"There is an intimate relationship between trace metals and organics. When you're getting a good suntan, melanin forms in your skin. There are many forms of melanin, and some are found in the dark feathers of birds, but copper is always bound into its structure," Manning said. "You can see this in living animals, but it's only since we've been using a synchrotron — a vast accelerator that generates intense X-rays a hundred million times brighter than the sun — that we can see the chemical detail in fossils and show that the copper complexes we found were originally part of the animal."
Metallic compounds can survive in these fossils for hundreds of millions of years because they are unpalatable to microorganisms. But to distinguish the copper that was bound in melanin with copper that might have been geochemically produced requires the precision that only a tool like the synchrotron can provide. By measuring the energy released by atoms when they are bombarded with high-powered X-rays, researchers can get an accurate picture of the molecules in which they reside.
"We're able to map absolute quantities, to parts-per-million levels in discrete biological structures, which we compare with living organisms and see they are comparable," Manning said.
The new technique paints a richer picture of the lives of these ancient creatures.
"If we could eventually give colors to long extinct species, that in itself would be fantastic," said co-author Uwe Bergmann, deputy director of the Linac Coherent Lightsource at SLAC. "But synchrotron radiation has revolutionized science in many fields, most notably in molecular biology. It is very exciting to see that it is now starting to have an impact in paleontology, in a way that may have important implications in many other disciplines,"
The team is confident that further research with this technique will enable them to fully diagnose color via fossil chemistry, and they also believe that this is only one of many applications the technique will have.
"This synchrotron research is really important as it gives us the first clue to really understanding what happens with organic debris when you bury it in the ground," Manning said. "For example, there are huge implications for understanding the mass transfer of buried waste; trace metals can be bad if you get too much of them, so we can spatially map and give images of exact loadings of these metals in both living and extinct organisms. No one else can do this. It's not just contributing to a field, it's creating a whole new discipline."