Signs of red pigment were spotted in a fossil for the first time

The 3-million-year-old mouse wore red.

For the first time, chemical traces of red pigment have been detected in a fossil, scientists say.

Using a technique called X-ray spectroscopy, researchers led by paleontologist Phillip Manning at the University of Manchester in England searched the fossil for a chemical signature associated with pheomelanin, the pigment responsible for reddish-brown fur or feathers. The team had already worked out which unique combination of chemical components stand for pheomelanin and for eumelanin, a dark brown or black pigment, by mapping out where trace metals such as zinc and copper bonded to organic molecules in the pigments of modern bird feathers. Pheomelanin, they determined, occurs where zinc binds to organic sulfur molecules.

Mapping where both zinc and sulfur molecules occurred on the mouse’s body revealed that the ancient field mouse had reddish-brown fur on its back and sides, the team reports online May 21 in Nature Communications.

Pheomelanin is difficult to preserve, though scientists previously have found hints of the red color in ancient critters. Microstructures identified in some exceptionally well-preserved fossils may be pigment-bearing pods called melanosomes; the shapes of the pods in modern animals are linked to the types of pigment they contain (SN: 11/26/16, p. 24). For example, sausage-shaped melanosomes contain eumelanin, while meatball-shaped melanosomes hold pheomelanin. And an armored dinosaur that lived 110 million years ago may have had some red on it: Scientists detected benzothiazole in its fossil, a by-product of pheomelanin that can form when the pigment breaks down (SN Online: 8/3/17).