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Here's How We Now Know a 3-Million-Year-Old Mouse Had Red Fur

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The X-ray image of the 3 million year old mouse.  (SLAC)

Scientists can now “see” more accurately what long-extinct species looked like.

Researchers from the SLAC National Accelerator Laboratory in Menlo Park and the University of Manchester have created a chemical image of a 3-million year-old mouse, published Tuesday in Nature Communications.

The mouse doesn’t look too different from those scurrying around today. The major discovery was its coloring: It had red fur and a white stomach.

“Paleontology has concerned itself with what you can see with your naked eye,” said Nick Edwards, a SLAC researcher and co-author of the paper. “That was all we had as a tool for many years, decades even.”

But now, using X-ray fluorescence imaging, researchers can map elements like zinc and sulfur that function as color markers. Elements have a unique amount of energy, or wavelength, they emit when bombarded with light. Based on the location of those elements in fossils, scientists can reconstruct the animal’s coloring in real life.


The technique could lead to some new discoveries, Edwards said.

“It’s actually that chemistry that could tell us about another level of ancient life, as opposed to just, ‘Here’s how it looked, here’s how it may have moved.’ It’s really like how it may have functioned at the biological level.”

The experiment marked the first time scientists have been able to detect a chemical signature of pheomelanin — the same red form of melanin present in animals’ red hair today — in an extinct species.

SLAC researchers imaged the 3-million-year-old mouse. Using elemental markers like zinc and sulfur, they found it likely had red fur and a white stomach.

The technique has some limitations. Edwards explained it can’t use elements to pick up bright blues, yellows, greens and pinks.  Only melanin pigments incorporate trace metals into their structure.

SLAC and University of Manchester researchers are also using the method to uncover the original writing on an ancient medical manuscript. Beyond that, the same approach may be used to investigate how pollution moves deep underground over thousands to millions of years, Edwards says.

In small doses, elements like zinc, copper and magnesium are harmless. But in larger doses, these same elements can be harmful to human health. So the team is exploring how they could use 3D imaging and X-ray fluorescence to investigate the paths metals take through layers of soil and rock.

“When we go and dump some organic materials and chemicals into the ground, how are those sort of taken up?” Edwards said. “Understanding how this kind of matter degrades and lasts over tens of millions of years is pretty important.”

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