Seeing Red in the Fossil Record


What color was T. Rex? What about triceratops or glyptodon? Until recently, the palette of prehistory was the sole provenance of daydreams, CGI artists or kids with crayons.

Advances in imaging technology are bringing us closer to real answers. Over the past decade, we’ve learned that Sinosauropteryx’s tail was striped, and Microraptor’s head was blue-black and shiny, like a crow’s.

A paper published Tuesday in Nature Communications adds to the paint box. In it, a team of researchers provide the first conclusive fossil evidence that an ancient creature contained pheomelanin — the same pigment that gives a red hue to chicken feathers, tiger fur and your freckles. Their findings, and the method that led to them, will allow researchers to search for more evidence of this coloring across the fossil record.

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Even in well-preserved fossils, pigments deteriorate quickly. Researchers have a few workarounds to find clues to color. Some look for melanosomes, the organelles in animal cells that make and store pigments. The shape of a melanosome can indicate what type of pigment was once inside, while the organization of melanosomes within a feather can suggest whether a bird (or dinosaur) was dull or iridescent.

Next, the team used spectroscopy to zoom in on two key elements: zinc and sulfur. In mammals and birds living today, pheomelanin is closely associated with particular zinc-sulfur compounds. The researchers saw these in the fossils as well, meaning their fur had been filled with the reddish pigment. They found a higher concentration of them on the dorsal side, suggesting the mouse had a lighter-colored belly.

“By understanding that delicate relationship between zinc and sulfur, for the first time, we can confidently say, ‘Yes, this is pheomelanin pigment in the fossil record,’” Dr. Manning said.

More important than their conclusion about the mouse’s color is what their process makes possible. Previous approaches to detecting color were piecemeal or destructive. But “this new method appears to allow mapping of color-giving pigments across a whole fossil,” without chipping any of it away, said Mike Benton, a paleontologist at the University of Bristol who was not involved in the study.

The group is working on further streamlining the scanning method, “so that it’s easy for anyone to come and bring in fossils,” Dr. Bergmann said.

Prehistoric world, get ready to start blushing.



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