Structural colours in diverse Mesozoic insects

Structural colours, nature’s most pure and intense colours, originate when light is scattered via nanoscale modulations of the refractive index. Original colours in fossils illuminate the ecological interactions among extinct organisms and functional evolution of colours. Here we report multiple examples of vivid metallic colours in diverse insects from mid-Cretaceous amber. Scanning and transmission electron microscopy revealed a smooth outer surface and five alternating electron-dense and electron-lucent layers in the epicuticle of a fossil wasp, suggesting that multilayer reflectors, the most common biophotonic nanostructure in animals and even plants, are responsible for the exceptional preservation of colour in amber fossils. Based on theoretical modeling of the reflectance spectra, a reflective peak of wavelength of 514 nm was calculated, corresponding to the bluish green colour observed under white light. The green to blue structural colours in fossil wasps, beetles, and a fly mo...