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. 2019 May 21;10(1):2250.
doi: 10.1038/s41467-019-10087-2.

Pheomelanin Pigment Remnants Mapped in Fossils of an Extinct Mammal

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Free PMC article

Pheomelanin Pigment Remnants Mapped in Fossils of an Extinct Mammal

Phillip L Manning et al. Nat Commun. .
Free PMC article

Abstract

Recent progress has been made in paleontology with respect to resolving pigmentation in fossil material. Morphological identification of fossilized melanosomes has been one approach, while a second methodology using chemical imaging and spectroscopy has also provided critical information particularly concerning eumelanin (black pigment) residue. In this work we develop the chemical imaging methodology to show that organosulfur-Zn complexes are indicators of pheomelanin (red pigment) in extant and fossil soft tissue and that the mapping of these residual biochemical compounds can be used to restore melanin pigment distribution in a 3 million year old extinct mammal species (Apodemus atavus). Synchotron Rapid Scanning X-ray Fluorescence imaging showed that the distributions of Zn and organic S are correlated within this fossil fur just as in pheomelanin-rich modern integument. Furthermore, Zn coordination chemistry within this fossil fur is closely comparable to that determined from pheomelanin-rich fur and hair standards. The non-destructive methods presented here provide a protocol for detecting residual pheomelanin in precious specimens.

Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Optical and X-ray images of Apodemus atavus “lateral” fossil. a Optical image of “lateral” fossil A. atavus (GZG.W.20027b) with the inset of extant A. sylvaticus in the upper right for comparison (scale bars = 1 cm). b False-color SRS-XRF image reveals exceptional preservation of integument as well as bone. This image is a combination of three maps, two standard single-element maps (blue = P, green = Zn), plus a third map which has been produced to especially emphasize the distribution of a specific oxidation state of organic sulfur (red = S in thiol) in order to highlight the clear correlation between the distribution of Zn and organic sulfur which together appear as bright yellow. (Optical photograph by P.L.M.)
Fig. 2
Fig. 2
X-ray image comparison of “lateral” and “dorsal” fossils. SRS-XRF map comparisons for the A. atavus lateral fossil (GZG.W.20027b: ac) with the “dorsal” fossil (GZG.W.17393a: dg). Maps a and d are total sulfur (incident beam energy 3150 eV). b and e show reduced organic species of sulfur (incident beam energy 2472.5 eV). c and f subtract the organic image from the total sulfur map, thus showing only inorganic sulfate. g is a false-color map (blue = P, green = Zn, and red = organic S) for the dorsal fossil comparable to that shown in Fig. 1b for the lateral fossil (scale bars = 1 cm). Bright yellow areas indicate a correlation between Zn and organic sulfur
Fig. 3
Fig. 3
Sulfur K-edge XANES data for standard, extant, and fossil specimens. The sulfur standards, A benzothiazole, a benzosulfur compound and a key component of pheomelanin, B Zn–cysteine, a terminal S organic functional group where we have substituted Zn for H as the exchangeable cation to simulate the configuration expected in pheomelanin tissue or its residue, C oxidized glutathione (disulfide) comparator for the dominant sulfur component in keratin, D methionine sulfoxide, an oxidized form of organic sulfur, and E Zn sulfate. The two extant mice spectra are presented along with linear combination fits (dashed lines) computed as a binary benzothiazole/disulfide system. The red circles highlight the resonance which is strong in the benzothiazole standard and which is resolvable in the red fur. The dashed vertical line furthermore indicates energy where the dominant benzothiazole peak is coincident with the second oscillation in the bifurcated disulfide peak to subtly shift the intensity of that second peak relative to the first—a shift that is discernible in the red fur but not the albino fur. Normalized spectra from the fossil are presented along with LCF fits calculated using all five standards as possible components (ratios of each standard contribution to the fits are given as a set of five numbers in parentheses). Because the fossil bone and sedimentary matrix are almost pure sulfate, for clarity fits have been omitted. Fits are shown as dashed lines for the three soft tissue analyses
Fig. 4
Fig. 4
Zinc X-ray absorption spectroscopy for fossils and standards. a Zinc K-edge XANES spectra for the fossil and extant mouse specimens, human hair, Zn-bonded eumelanin, Zn–acetate heptahydrate, and ZnS. The two vertical lines indicate the absorption spectrum maxima for pure first shell Zn–S and pure first shell Zn–O species. b First-derivative analysis in the vicinity of the sulfur “white line” region. The ZnS spectrum is displaced to the low-energy side and the Zn–O spectrum from Zn-substituted eumelanin is displaced toward high energy, with the two pheomelanin bearing hair standards intermediate between the two. c Fourier-transformed EXAFS showing relative positions of backscatterers around the Zn central absorber. The heavy dashed line indicates the Zn–S shell. All labels on the vertical lines refer to element shells given in Table 1. Note that the distance values in this figure are not phase shifted and hence are smaller than those presented in the table, but relative positions remain the same. d The two Zn coordination environments resolved in both the extant hair and fur and in the fossil mouse fur. The high abundance of organosulfur-bonded Zn in the fur and skin regions of the A. atavus fossil is most likely due to an originally high concentration of pheomelanin which is enriched in the tetrahedrally coordinated Zn complex shown in the right of the panel. (Zn = dark gray; C = light gray; O = red; S = yellow; N = blue; H = white)

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References

    1. Edwards NP, et al. Elemental characterisation of melanin in feathers via synchrotron X-ray imaging and absorption spectroscopy. Sci. Rep. 2016;6:34002. doi: 10.1038/srep34002. - DOI - PMC - PubMed
    1. Wogelius RA, et al. Trace metals as biomarkers for eumelanin pigment in the fossil record. Science. 2011;333:1622–1626. doi: 10.1126/science.1205748. - DOI - PubMed
    1. Manning PL, et al. Synchrotron-based chemical imaging reveals plumage patterns in a 150 million year old early bird. J. Anal. Spectrom. 2013;28:1024–1030. doi: 10.1039/c3ja50077b. - DOI
    1. Harazim D, et al. Bioturbating animals control the mobility of redox sensitive trace elements in organic rich mudstone. Geology. 2015;34:1007–1010. doi: 10.1130/G37025.1. - DOI
    1. Barden HE, et al. Geochemical evidence of the seasonality, affinity and pigmentation of Solenopora jurassica. PLoS ONE. 2015;10:e0138305. doi: 10.1371/journal.pone.0138305. - DOI - PMC - PubMed

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