Bird fossils reveal life's colourful chemistry
The pigments preserved in fossils, including a 120 million-year-old bird, have been revealed using X-rays.
A team, led by scientists from the University of Manchester, UK, scanned the beautifully preserved fossils.
Their study, published in the journal Science, revealed the chemical fingerprint of pigments that once tinted the ancient bird's feathers.
Manchester palaeontologist Phil Manning described the discovery as an insight into "the chemistry of life itself".
As well as the colour patterns of ancient creatures, pigments reveal fundamental clues about the chemical reactions that took place in their bodies, and the food the creatures ate that fuelled those reactions.
Dr Manning, his Manchester colleague Roy Wogelius and Uwe Bergmann from the SLAC National Accelerator Laboratory in California, led the international team. They used a powerful X-ray source called a synchrotron, which uncovered metals within the ancient fossilised feathers.
"These trace metals, specifically copper, is a [marker] for a dark pigment called eumelanin," explained Dr Wogelius. This X-ray technique was so sensitive that it was able to show that each molecule of copper it detected was being tugged and squashed into a particular shape because it was bound within a eumelanin molecule.See the dark
The X-rays acted as probes, detecting the individual chemical building blocks that make up the fossil. When the rays hit the fossil, the signal that bounces back depends on the shape and size of each molecule, and how it is being subtly influenced by the chemicals surrounding it.
The team used this powerful probe to scan fossilised remains of two ancient birds: 110 million-year-old Gansus yumenensis, the oldest example of a modern bird in the fossil record, and 120 million-year-old Confuciusornis sanctus, the earliest beaked bird.
This revealed, not only that the dark pigment molecules were an intrinsic part of the chemical matrix of the birds' feathers, but that they were perfectly preserved for up to 120 million years. This allowed the researchers to paint a monochrome picture of both ancient creatures.
Dr Wogelius said: "[Eumelanin] controls the dark and light patterns of an animal, so for Confuciusornis sanctus, for example, we can see that its body and the neck were black and its wings were patchy.
"For years people had been looking at these fossils thinking that the feathers were just impressions. We showed that they have chemistry."
Previous attempts to diagnose the colour of long extinct animals focused on pigment "containers" in feathers known as melanosomes. But these biological paint pots, Dr Manning explained, do not survive well in ancient fossils.
"But the pigments they once contained do, courtesy of their copper heart - even after the melanosome containing them has been destroyed," he told BBC Nature.
The new technique will allow scientists to study the chemistry of more fossils, without having to damage them by removing samples. For many fossils, this is an important consideration; an Archaeopteryx specimen the group studied last year has been valued at an estimated $6 million (£3.75 million).
End Quote Phil Manning University of Manchester
The potential for this technique to gently un-pick the chemistry of long extinct species is quite breathtaking”
Dr Phil Manning said that the findings showed the "potential for unlocking the prehistoric colour palette", but that they also contained more fundamental clues about ancient life.
"This offers insight to the [biochemistry] that governed life tens or even hundreds of millions years ago," he told BBC Nature.
Since metals, including zinc and copper, form part of many animals' diets, so mapping them in fossils could shed light on what the animals fed on 100 million years ago.
And since one of the key roles of pigmentation is camouflage, pigmentation could tell us more about the world around the animal and what it was trying to blend into.
Dr Manning said: "The potential for this technique to gently un-pick the chemistry of long extinct species is quite breathtaking."
"We can even start treating the fossil record as a long-term experiment for burying organic compounds in different environments and then studying what happens to them through deep geological time," he said.
"So it could help us understand what happens when you bury something like biowaste in the ground.
"We could really understand what happens to something when its buried for 120 million years; this goes way beyond palaeontology."