THE ORIGINAL COLORS OF FOSSIL MOTHS

Fossilization of soft tissues in exceptionally preserved fossils has the potential to aid reconstructions of the morphology and appearance of ancient organisms. Recent studies of fossil birds and dinosaurs show that preserved pigmentary microstructures in fossil feathers can be used to reconstruct the original coloration. Exceptionally preserved fossils can also exhibit evidence of structural color, which is generated by scattering of light by periodic variations in tissue nanostructure. Structural colors function primarily in communication and are widespread in nature today, but the feasibility of their being fossilized, and thus their fossil record, have received little attention. As a result, the evolution of structural coloration and its functions in animals is poorly understood. This is particularly significant for the Lepidoptera (butterflies and moths), which exhibit the most complex and diverse structural colors of any extant group. Here we report the preservation of structurally colored scales in fossil lepidopterans from the ~47 million-year-old Eocene Grube Messel oil shales (Germany) and reconstruct the original colors of their wings. Specimens exhibit bright, non-iridescent metallic hues which are generated by a multilayer reflector comprised of a stack of perforated laminae in the scale lumen; differently colored scales differ in their ultrastructure. The original colors were altered during fossilization but can be reconstructed based upon preserved ultrastructural detail. Coloration is brightest on the dorsal forewing surfaces, indicating a defensive function. This visual signal was enhanced by suppression of iridescence (change in hue with viewing angle) achieved by two different optical mechanisms: extensive perforation, and concave distortion, of the multilayer reflector. The fossils provide the first evidence for the function of structural color in the fossil record and confirm the feasibility of reconstructing color in non-metallic lepidopteran fossils.