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Art & Artifacts

Method maps reddish pigment in fossil

Correlation of sulfur and zinc suggests distribution of pheomelanin

by Celia Henry Arnaud
May 26, 2019 | APPEARED IN VOLUME 97, ISSUE 21

Credit: Nat. Commun.
Credit: University of Göttingen
This image (top) shows the distributions of phosphorus (blue), zinc (green), and organosulfur (red) in a 3-million-year-old fossilized mouse (optical image shown on bottom). The colocalization of zinc and sulfur (yellow) suggests the presence of pheomelanin.

Two types of melanins are involved in coloration of animal skin and fur. Eumelanin is associated with black and dark brown hues, whereas pheomelanin is associated with lighter reddish-brown shades. Knowing how these pigments are distributed in fossilized soft-tissue remains can help scientists understand what extinct animals looked like. But detecting them in fossilized remains is hard. Scientists have previously detected eumelanin in fossils, but pheomelanin has been more elusive. Now, an international team led by Roy A. Wogelius, a geochemist at the University of Manchester, has found a signature for pheo­melanin in a 3-million-year-old fossil of Apodemus atavus, an extinct relative of modern field mice (Nat. Commun. 2019, DOI: 10.1038/s41467-019-10087-2). Scientists know that sulfur in pheo­melanin forms complexes with zinc. So in the new study, the researchers went looking for sulfur and zinc in the fossilized mouse. They analyzed the elements using X-ray spectroscopy and mapped the distributions of zinc, phosphorus, and organosulfur using synchrotron X-ray fluorescence imaging. The distributions of zinc and organosulfur were correlated in much the same way as in pheomelanin-containing modern hair and fur, suggesting this prehistoric mouse sported at least some reddish-brown fur. The method should be applicable to other fossils.

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