Pigments produce colour by the selective absorption of certain wavelengths of visible light. Typical pigments include melanins, carotenoids (bright reds and yellows) and porphyrins (greens, reds and blues). Other colours – known as structural colours — are produced by light scattering nanostructures. (The brilliant iridescent colours on a peacock’s tale, for example.) Melanin controls, among other things, our hair and eye colour. It is produced and stored in tiny cellular bags called melanosomes, and these come in two forms. A sausage-shaped type produces black shades; a round-shaped variety creates rusty reddish hues.
Combinations of these melanins alongside absence of pigment create grey, brown and white colours. If pigments had been preserved in the ink sacs, Vinther reasoned, then melanin – or the melanin-bearing melanosomes – might also be found in fossilised skin and feathers.
He found his answer in the fossil skull of a small, 55-million-year-old bird from his home country of Denmark, preserved with a dark halo of feather impressions and two stains where the eyes use to be. “I was sat there [looking for evidence of melanosomes] zooming in with the microscope, and suddenly I was like, blimey, they’re there! We can put colours in fossil dinosaurs.”