title: Chemical, experimental, and morphological evidence for diagenetically altered melanin in exceptionally preserved fossils.
abstract: 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.
authors.affiliation: School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom; Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24060;
authors.forename: Caitlin
authors.initials: C
authors.lastname: Colleary
authors.affiliation: Texas Materials Institute, University of Texas at Austin, Austin, TX 78712;
authors.forename: Andrei
authors.initials: A
authors.lastname: Dolocan
authors.affiliation: Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78712;
authors.forename: James
authors.initials: J
authors.lastname: Gardner
authors.affiliation: School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom;
authors.forename: Suresh
authors.initials: S
authors.lastname: Singh
authors.affiliation: Department for the Conservation of the Cultural Heritage of Rhineland-Palatinate, 55116 Mainz, Germany;
authors.forename: Michael
authors.initials: M
authors.lastname: Wuttke
authors.affiliation: Department of Palaeoanthropology and Messel Research, Senckenberg Research Institute, 60325 Frankfurt am Main, Germany;
authors.forename: Renate
authors.initials: R
authors.lastname: Rabenstein
authors.affiliation: Department of Palaeoanthropology and Messel Research, Senckenberg Research Institute, 60325 Frankfurt am Main, Germany;
authors.forename: Jörg
authors.initials: J
authors.lastname: Habersetzer
authors.affiliation: Department of Palaeoanthropology and Messel Research, Senckenberg Research Institute, 60325 Frankfurt am Main, Germany;
authors.forename: Stephan
authors.initials: S
authors.lastname: Schaal
authors.affiliation: Paleoanthropology and Paleoenvironment Program, School of Earth Sciences, College of Natural Sciences, Addis Ababa University, Addis Ababa, Ethiopia;
authors.forename: Mulugeta
authors.initials: M
authors.lastname: Feseha
authors.affiliation: Roy M. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, TX 75275;
authors.forename: Matthew
authors.initials: M
authors.lastname: Clemens
authors.affiliation: Roy M. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, TX 75275;
authors.forename: Bonnie F
authors.initials: BF
authors.lastname: Jacobs
authors.affiliation: Departments of Botany and Geology & Geophysics, University of Wyoming, Laramie, WY 82071;
authors.forename: Ellen D
authors.initials: ED
authors.lastname: Currano
authors.affiliation: Roy M. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, TX 75275;
authors.forename: Louis L
authors.identifier: http://orcid.org/0000-0002-7735-3678
authors.initials: LL
authors.lastname: Jacobs
authors.affiliation: Division of Natural History, Muse®um, 7800 Skive, Denmark;
authors.forename: Rene Lyng
authors.initials: RL
authors.lastname: Sylvestersen
authors.affiliation: Department of Geology, University of Leicester, Leicester LE1 7RH, United Kingdom;
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Gabbott
authors.affiliation: School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom; Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78712; School of Biological Sciences, University of Bristol, Bristol BS8 1TQ, United Kingdom jakob.vinther@bristol.ac.uk.
authors.forename: Jakob
authors.initials: J
authors.lastname: Vinther
mesh_terms: D000818:Animals; D001419:Bacteria; D005580:Fossils; D008543:Melanins; D020460:Melanosomes / Q000648:ultrastructure*; D010858:Pigmentation
chemical_list: D008543:Melanins
keywords: diagenesis; mass spectrometry; melanosome; paleocolor; pigmentation