Ink sacs found in two 160-million-year-old giant cephalopod fossils have been found to contain ink that's essentially identical to that of today's cuttlefish.
The discovery implies that the ink-screen escape mechanism of cephalopods such as cuttlefish, squid and octopuses hasn't evolved since the Jurassic period, and that melanin could be preserved intact in the fossils of other creatures.
"Though the other organic components of the cephalopod we studied are long gone, we've discovered through a variety of research methods that the melanin has remained in a condition that could be studied in exquisite detail," says John Simon of the University of Virginia.
One of the ink sacs, found in Wiltshire, England, is the only intact ink sac ever discovered. The chemical composition of the fossil melanin was compared to that of the modern cuttlefish, Sepia officinalis, common to the Mediterranean, North and Baltic seas.
"It's close enough that I would argue that the pigmentation in this class of animals has not evolved in 160 million years," says Simon.
"The whole machinery apparently has been locked in time and passed down through succeeding generations of cuttlefish. It's a very optimized system for this animal and has been optimized for a long time."
It might seem surprising to find melanin after all this time, but it's highly resilient, says Simon.
"Out of all of the organic pigments in living systems, melanin has the highest odds of being found in the fossil record," he says. "That attribute also makes it a challenge to study. We had to use innovative methods from chemistry, biology and physics to isolate the melanin from the inorganic material."