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What color was T. Rex? What about triceratops or glyptodon? Until recently, the palette of prehistory was the sole source of daydreams, artists of CGI or kids with pencils.
Advances in imaging technology bring us closer to real answers. Over the past decade, we have learned that Sinosauropteryx's tail was striped and that Microraptor's head was black-blue and shiny, like that of a raven.
An article published Tuesday in Nature Communications adds to the paint box. A team of researchers provides the first conclusive fossil evidence that an ancient creature contained pheomelanin – the same pigment that gives red tinge to chicken feathers, tiger fur and freckles. Their discoveries and the method that led them will allow researchers to search for more evidence of this coloring in the fossil record.
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Even in well-preserved fossils, pigments deteriorate rapidly. Researchers have some workarounds to find clues about color. Some look for melanosomes, the organelles of 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 in a feather can suggest whether a bird (or dinosaur) was dull or iridescent .
Another technique is to search for more persistent molecules known to be associated with the pigments. This is the favorite tactic of this research group, which Traces of eumelanin – a brown and black pigment – have already been found in the plumage of the Archeopteryx feathered dinosaur.
For this new study, researchers worked with two specimens of an extinct mouse, Apodemus atavus. Three million years ago, several of these mice died and were dragged into a pond in present-day Willershausen, Germany. Quickly buried by the sediments, they were spared by many ravages caused by bacteria and time, and ended up in a fossil drawer at the Geoscience Museum of the University of Göttingen.
Phillip Manning spotted them in the museum's collection a few years ago.
"I have seen the exceptional conservation of fur," said Dr. Manning, a geologist at the University of Manchester and senior author of the journal. "I realized," Damn it, it'll be worth it to be scanned! ""
The mice were sent to the SLAC National Accelerator Laboratory in California, where they were passed through a special x-ray that revealed their chemical structure. The X-ray runs on a scale fine enough to detect "a little sulfur, or a little bit of zinc or copper," said Uwe Bergmann of Stanford, who operated the machine. "We can get cards of different items very quickly." (Dr. Bergmann initially proposed this technique in the early 2000s to reveal the ink of the erased and occluded pages of the Archimedean palimpsest.)
The team then used spectroscopy to zoom in on two key elements: zinc and sulfur. In mammals and birds living today, pheomelanin is closely associated with some zinc-sulfur compounds. The researchers also saw them in the fossils, which means that their fur was filled with reddish pigment. They found a greater concentration of them on the dorsal side, suggesting that the mouse had a lighter colored belly.
"By understanding this delicate relationship between zinc and sulfur, we can say for the first time with confidence," Yes, it is a pheomelanin pigment in the fossil record, "said Dr. Manning.
What their process makes possible is more important than their conclusion about the color of the mouse. Previous approaches to detecting color were fragmentary or destructive. But "this new method seems to map color pigments through an entire fossil," without cutting any, said Mike Benton, a paleontologist from Bristol University who did not participate in the study. 39; study.
The group is currently working to further streamline the digitization method, "so that everyone can easily come in search of fossils," said Dr. Bergmann.
Prehistoric world, get ready to blush.
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