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Researchers have for the first time detected chemical traces of red pigment in an ancient fossil – an exceptionally well-preserved mouse, similar to today's field mice – that roamed the fields of what is now the German village of Willershausen about 3 million years ago.
The study found that the missing creature, affectionately nicknamed "the powerful mouse" by the perpetrators, was wearing a brown to reddish fur on the back and sides and that she was wearing a small white belly. The results were published today in Nature Communications.
The international collaboration, led by researchers at the University of Manchester in the UK, has used X-ray spectroscopy and multiple imaging techniques to detect the delicate chemical signature of pigments in this long-extinct mouse.
"Life on Earth has thrown into the fossil record a wealth of information that science has only recently been able to access," says Professor Phil Manning of Manchester, who led the study. "A series of new imaging techniques can now be deployed, which allows us to thoroughly analyze the chemical history of a fossil organism and the processes that have preserved its tissues." Before, we simply discovered minerals, but we gently decap the 'biochemical ghosts' of long gone species. "
The research team, made up of scientists from the US Department of Energy's National SLAC Accelerator Laboratory, used x-ray beams from the Stanford synchrotron radiation source (SSRL) and the diamond light source (DLS) of SLAC in the United Kingdom.
Paint an image of the past
Color plays a vital role in the selective processes that have guided evolution for hundreds of millions of years. But until recently, the techniques used to study fossils were not able to explore the pigmentation of ancient animals that is essential to reconstruct exactly what they look like.
This very recent article marks a breakthrough in the ability to resolve fossilized color pigments in extinct species by mapping the key elements associated with melanin pigment, the dominant pigment in animals. In the form of eumelanin, the pigment gives a black or dark brown color, but in the form of pheomelanin, it produces a reddish or yellow color.
Build the foundation
Until recently, researchers have focused on the trace elements known to be associated with eumelanin, revealing in previous experiments dark and light patterns in the feathers of early birds, notably Archeopteryx, the famous fossil that for the first time offered a clear link between dinosaurs and birds.
In 2016, co-author Nick Edwards, a scientist at SLAC, led a study demonstrating the potential for differentiation between eumelanin and pheomelanin in modern bird feathers. These works provided a chemical reference for this most recent article, which showed for the first time that it was possible to detect the elusive red pigment, which is much less stable over geological time, in ancient fossils.
"We had to create a solid foundation using modern animal tissues before we could apply the technique to these ancient animals," Edwards said. "It was really a critical point in the use of chemical signatures to break the staining of old animals with soft tissue fossils."
To reveal the fossil patterns of the powerful mouse, the Manchester team used SSRL and DLS to give the fossils intense x-rays. The interaction of these X-rays with the traces of metals present in the pigments allowed the team to reconstruct the reddish coloration of the coat of the mouse.
"The fossils used in this study preserve astonishing structural details, but our work emphasizes that this outstanding preservation can also lead to extraordinary chemical details that change our understanding of what can be solved in fossils," he said. said Manchester geochemistry professor Roy Wogelius. co-directed the study. "Along the way, we learned a lot about the chemistry of pigmentation throughout the animal kingdom"
Adding a new dimension
The key to their work was to determine that trace metals were incorporated into fossilized mouse fur in the same way that they bind to pigments in animals with a high concentration of red pigment in their tissues.
"If you're doing research in a particular field, the framework of your techniques may change," says Uwe Bergmann, co-author and distinguished scientist at SLAC, who led the development of X-ray fluorescence X-ray imaging. used in this research. "The hope is that you can develop a tool that will become part of the standard arsenal when something new will be studied, and I believe that the application to fossils is a good example."
The efforts, which have involved physics, paleontology, organic chemistry and geochemistry, inform scientists of what to look for in the future.
"We hope these results will allow us to strengthen our confidence in reconstructing missing animals and thus add another dimension to the study of evolution," said Wogelius.
NATIONAL LABORATORY OF ACCELERATORS DOE / SLAC
Header Image – Using SLAC's Stanford synchrotron radiation light source, researchers were able to unravel the story of essential pigments in ancient mouse fossils. The researchers showed that the mouse probably had a reddish-brown fur on the back and sides and a white belly, as shown by Stuart Pond's artist's design on the left. The bottom right image is a photo of the key fossil examined in this study. Above is a synchrotron X-ray image in false colors of fossil chemistry. Credit: Gregory Stewart / SLAC National Accelerator Laboratory
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