Color has long been a persistent problem in scientists’ efforts to reconstruct the appearances of ancient creatures. Soft tissues like feathers and fur are rarely preserved in the fossil record — and when these substances are found, their hues have long since disappeared. But an international team of researchers led by experts at the University of Manchester recently made an important breakthrough in figuring out the colors of prehistoric animals, as Gretchen Vogel reports for Science. Using a non-invasive technique, the researchers were able to determine that a three-million-year-old mouse had reddish fur, marking the first time that chemical traces of a red pigment have been detected in an ancient fossil.
The study was based on two exceptionally well-preserved fossils of a little rodent — formally known as Apodemus atavus, but the researchers dubbed it “mighty mouse”— discovered in Germany. “What we found is that the mouse is preserved in absolutely stunning detail, nearly all of the skeleton and most of the soft tissue of the body, head, feet, and tail can easily be recognized,” Uwe Bergmann, study co-author and physicist at the SLAC National Accelerator Laboratory, tells CNN’s Ashley Strickland.
To learn more about the mouse’s coloring, scientists looked to melanin, an important pigment dictating color in ancient and modern animals. There are two main melanin pigments in animal tissues: eumelanin, which imparts a black, brown or grey color, and pheomelanin, which is responsible for pink and red hues. Until recently, investigations into the colors of prehistoric creatures have focused on detecting the chemical residues of eumelanin, but pheomelanin proved trickier to find because it is much less stable over geological time.
But in 2016, a study led by SLAC paleontologist Nick Edwards showed that it was possible to map the elements that make up red and black pigments in the feathers of modern birds using x-ray technology. For instance, the researchers found that zinc bonded to sulphur in a specific way was indicative of red-hued pheomelanin. And zinc in the absence of sulphur was a reliable indicator of black eumelanin.
“We had to build up a strong foundation using modern animal tissue before we could apply the technique to these ancient animals,” Edwards explains. “It was really a tipping point in using chemical signatures to crack the coloring of ancient animals with soft tissue fossils.”
For the new study, published in Nature Communications, scientists pelted the mighty mouse fossils with intense x-rays to see how they interacted with trace metals preserved in the animals’ fur. And the team could see that these metals were bonded to organic chemicals in the same way that they bond to organic chemicals in extant animals with red pigments in their tissue. The researchers also discovered that while the fur on the mouse’s back and sides was red, its belly was white.
“Where once we saw simply minerals, now we gently unpick the ‘biochemical ghosts’ of long extinct species,” says Phil Manning, the study's first author and professor of natural history at the University of Manchester.
Crucially, and in contrast to other types of chemical analyses, the researchers’ methods did not require them to take a sample from the fossils, which inevitably would have damaged them. And the study authors anticipate that their findings will help experts paint a more vivid picture of other extinct animals.
“We understand now what to look for in the future,” explains Roy Wogelius, study co-author and geochemist at the University of Manchester. “And our hope is that these results will mean that we can become more confident in reconstructing extinct animals and thereby add another dimension to the study of evolution.”