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Melanin confirmed preserved in fossils
A new paper:
Caitlin Colleary, Andrei Dolocan, James Gardner, Suresh Singh, Michael
Wuttke, Renate Rabenstein, Jörg Habersetzer, Stephan Schaal, Mulugeta
Feseha, Matthew Clemens, Bonnie F. Jacobs, Ellen D. Currano, Louis L.
Jacobs, Rene Lyng Sylvestersen, Sarah E. Gabbott, and Jakob Vinther
Chemical, experimental, and morphological evidence for diagenetically
altered melanin in exceptionally preserved fossils.
Proceedings of the National Academy of Sciences (advance online publication)
Melanin is a widespread pigment that provides black to reddish brown
hues to organisms. Recent evidence has shown that melanin is retained
in exceptionally preserved fossils, including feathered dinosaurs,
allowing the reconstruction of ancient color patterns. However, little
is known about the chemical preservation of melanin or its
distribution in the fossil record. Here, we show that melanin is
preserved in a number of soft-bodied fossils, but its burial under
high pressure and temperature for millions of years alters its
original chemistry. The widespread occurrence of melanin substantiates
the applicability of reconstructing aspects of original color patterns
and allows us to dismiss the alternative suggestion that these
structures are microbial in origin.
In living organisms, color patterns, behavior, and ecology are closely
linked. Thus, detection of fossil pigments may permit inferences about
important aspects of ancient animal ecology and evolution.
Melanin-bearing melanosomes were suggested to preserve as organic
residues in exceptionally preserved fossils, retaining distinct
morphology that is associated with aspects of original color patterns.
Nevertheless, these oblong and spherical structures have also been
identified as fossilized bacteria. To date, chemical studies have not
directly considered the effects of diagenesis on melanin preservation,
and how this may influence its identification. Here we use
time-of-flight secondary ion mass spectrometry to identify and
chemically characterize melanin in a diverse sample of previously
unstudied extant and fossil taxa, including fossils with notably
different diagenetic histories and geologic ages. We document
signatures consistent with melanin preservation in fossils ranging
from feathers, to mammals, to amphibians. Using principal component
analyses, we characterize putative mixtures of eumelanin and
phaeomelanin in both fossil and extant samples. Surprisingly, both
extant and fossil amphibians generally exhibit melanosomes with a
mixed eumelanin/phaeomelanin composition rather than pure eumelanin,
as assumed previously. We argue that experimental maturation of modern
melanin samples replicates diagenetic chemical alteration of melanin
observed in fossils. This refutes the hypothesis that such fossil
microbodies could be bacteria, and demonstrates that melanin is widely
responsible for the organic soft tissue outlines in vertebrates found
at exceptional fossil localities, thus allowing for the reconstruction
of certain aspects of original pigment patterns.