X-rays reveal the colors of a 3 million-year-old fossil mouse

Enlarge / A false color synchrotron X-ray image of the fossil chemistry. Blue represents calcium in the bones, green is the element zinc, which has been shown to be important in the biochemistry of red pigment, and red is a particular type of organic sulfur that cannot be imaged by traditional methods. This type of sulfur is enriched in red pigment. When combined, regions rich in both zinc and sulfur appear yellow on this image, showing that the fur on this animal was rich in the chemical compounds that are most probably derived from the original red pigments produced by the mouse. (credit: Wogelius et al. 2019)

Here's something you don't hear often: the dead field mouse looks incredible for its age. It lived and died three million years ago in what is now Germany, but layers of rock preserved nearly its whole skeleton, along with most of the fur and skin on its body, feet, and tail. Even its tiny, delicate ears were preserved.

Thanks to new imaging methods and a better understanding of the chemistry behind pigment in animal fur and feathers, we now know that it had reddish-brown fur with a white underbelly. Paleontologists have had the tools to detect patterns of light and dark coloring in fossil feathers for a few years, but this is their first real glimpse of a colored pigment.

It comes in colors

The range of colors in animal fur comes from varying amounts of two types of a pigment called melanin. Eumelanin produces black or dark brown coloring, while pheomelanin creates reddish or yellow hues. Pheomelanin doesn't tend to hold up well over the millions of years most fossils are buried; eumelanin is more sturdy, which is why we have a decent idea about the patterns of light and dark in the feathers of Archaeopteryx and some of the other ancestors of today's birds.

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