Morphological and Geochemical Evidence of Eumelanin Preservation in the Feathers of the Early Cretaceous Bird, Gansus yumenensis

Abstract

Recent studies have shown evidence for the preservation of colour in fossilized soft tissues by imaging melanosomes, melanin pigment containing organelles. This study combines geochemical analyses with morphological observations to investigate the preservation of melanosomes and melanin within feathers of the Early Cretaceous bird, Gansus yumenensis. Scanning electron microscopy reveals structures concordant with those previously identified as eumelanosomes within visually dark areas of the feathers but not in lighter areas or sedimentary matrices. Fourier transform infrared analyses show different spectra for the feathers and their matrices; melanic functional groups appear in the feather including carboxylic acid and ketone groups that are not seen in the matrix. When mapped, the carboxylic acid group absorption faithfully replicates the visually dark areas of the feathers. Electron Paramagnetic Resonance spectroscopy of one specimen demonstrates the presence of organic signals but proved too insensitive to resolve melanin. Pyrolysis gas chromatography mass spectrometry shows a similar distribution of aliphatic material within both feathers that are different from those of their respective matrices. In combination, these techniques strongly suggest that not only do the feathers contain endogenous organic material, but that both geochemical and morphological evidence supports the preservation of original eumelanic pigment residue.

Molecular preservation of the pigment melanin in fossil melanosomes

“…These observations were corroborated by IR microspectroscopy consistent with previous infrared studies of fossil melanin 14,15 . The vibrational spectrum for the fossil microbodies is presented along with a spectrum for a natural melanin standard and other tissues absorbance spectra of various structures of Fum-n-2050 and a natural melanin standard.…”

“…The molecular analyses performed in this study demonstrate that the chemical composition of the fossil microbodies variably assigned to as bacterial biofilms 5,6,12 or melanosomes [8][9][10][11][14][15][16][17] , at least in FUM-N-2050, is dominated by melanin or a molecular structure very similar to this pigment. Although microorganisms can synthesize melanins 26 , we argue against the possibility that the melanin-containing structures represent replacement bacteria because the pigment is highly concentrated and localized specifically to melanosome-like bodies in a tissue where melanin must have been a major constituent in life (cf.…”

Molecular evidence of keratin and melanosomes in feathers of the Early Cretaceous bird Eoconfuciusornis

“…However, where chemical data were presented previously, with few exceptions (20,21) the data were not sufficiently specific to support or eliminate either hypothesis (22)(23)(24)(25)(26). Whether the melanin-related chemical signals originated from the microbodies or from the surrounding matrix (22)(23)(24)(25)(26) could not be determined, with the exception of one study by Lindgren et al (21).…”

Interpreting melanin-based coloration through deep time: a critical review

“…[7-10, 52-54,62]), whereas chemical studies, with few exceptions (see above), have either been inconclusive (e.g. [14,63]) or lacking in specificity and/or relevant comparative material to rule out alternative hypotheses (e.g. [55,64,65]).…”