Figuring out the colors of fossilized animals used to complete guesswork — even in the rare finds of feathers, scales, or the original . Now, for the first time, researchers have been able to identify the chemical signature of the pigment that gives red hair its color in the fossil of an ancient mouse — using a new technique that leaves precious fossil specimens intact.
“The mouse fossil, it looks nice. It's a beautiful specimen. But then you scan it, and it's this eureka moment, ”says Roy Wogelius, a geochemist at the University of Manchester in the United Kingdom, who developed his technique with his colleagues.
Using a variety of techniques, scientists have been able to gather hints about the colors of fossils including dinosaur feathers and dinosaur eggs. A decade ago, scientists used high-energy synchrotron x-rays to identify the key chemical signatures of a pigment called eumelanin, which colors skin, hair, and other tissues black, brown, and gray. Pheomelanin, which gives skin and hair a pink or red hue, has been down to nail down.
Part of the problem, Wogelius says, was relatively little known about the chemistry of the pigment in modern -day tissues. In work published in 2016, he and his colleagues looked carefully at the different trace metals in pigments from modern feathers and found that whereas eumelanin contains copper, pheomelanin contains sulfur and zinc. Signs of the reddish pigment in fossils as well
To test the idea, the scientists analyzed two exceptional fossils — with soft tissues and hair still visible — of an extinct mouse called Apodemus atavus who lived 3 million years ago in what is now Germany. Close relatives of the species alive today, as the European wood mouse, have reddish fur, so the researchers thought the fossil mouse might have had similar coloring. Sure enough, when they scanned the mouse fossils, they found the characteristic overlap of sulfur and zinc in regions where hair was visible on the fossil. They report their find today in Nature Communications
Now that scientists know what to look for, Wogelius says, he is confident the pheomelanin signature will be detectable in much older fossils. The new data support the team's previous claim of evidence for pheomelanin in a 30-million-year-old fossil tadpole. "I know we can go back 30 million years, and probably even longer than that."
The technique is "a very elegant method for analyzing the whole fossil in a non-destructive way," says Jasmina Weimann, a molecular paleobiologist at Yale University. "It's very cool."
Other chemical analysis methods require researchers to take tiny samples from fossils. Not only does that damage part of the fossil, it also means the full picture is still guesswork. "If you took a square-millimeter sample of zebra skin, you might be able to tell if the sample was black or white, but you wouldn't understand what a zebra looks like," Wogelius says.
Weimann hopes similar techniques might also be used to identify not only pigments, but also other chemical signatures, for example of proteins specific to certain tissues.