Trace Metals as Biomarkers for Eumelanin Pigment in the Fossil Record

See allHide authors and affiliations

Science  30 Jun 2011:
DOI: 10.1126/science.1205748


Well-preserved fossils of pivotal early bird and nonavian theropod species have provided unequivocal evidence for feathers and/or down-like integuments. Recent studies have reconstructed color based upon melanosome structure; however, the chemistry of these proposed melanosomes has remained unknown. Here, we apply synchrotron x-ray techniques to several fossil and extant organisms, including Confuciusornis sanctus, to map and characterize possible chemical residues of melanin pigments. Results show that trace metals, such as copper, are present in fossils as organometallic compounds most likely derived from original eumelanin. The distribution of these compounds provides a long-lived biomarker of melanin presence and density within a range of fossilized organisms. Metal zoning patterns may be preserved long after melanosome structures have been destroyed.