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The brownish-black fossil pigment is identical to modern squid ink - says a new study

Ink sac, which can be used to expel a cloud of dark ink to confuse predators hasn't evolved much since the prehistoric era.

Two ink sacs from 160-million-year-old giant cephalopod (cuttlefish, squid and octopuses) fossils were unearthed two years ago in England. They contained the pigment melanin, and it was found that it is essentially identical to the melanin in the ink sac of a modern-day cuttlefish.

The finding in an extremely rare case of being able to study organic material that is hundreds of millions of years old suggests that the ink-screen escape mechanism has not evolved since the prehistoric time, and that melanin could be preserved intact in the fossils of a range of organisms.

“Scientists have previously found hints of eumelanin in fossils, but they've done it through indirect, less reliable means; such as by analyzing images of presumed granules, which is problematic in part because melanin granules resemble bacteria,” said study co-author John Simon. The most common form of biological melanin is eumelanin, a brown-black polymer of dihydroxyindole carboxylic acids, and their reduced forms.

Now Simon and colleagues have used a variety of direct, high-resolution chemical techniques; including scanning electron microscopy and mass spectrometry, which measures light wavelengths to uncover chemical signatures to identify eumelanin in the fossilized ink sacs.

The ink sacs somehow escaped decomposition, providing scientists with "exceptional" soft tissue specimens, the study says. "We all got pretty excited about looking at these ancient fossils," said Simon.

"As we look back and think about what we know about life before our time, it's mostly through skeletal info," Simon said. "What's beginning to happen now is that people are realizing that, in addition, there is soft tissue that's being preserved.”
Studying soft tissue, he added, "could give us a whole new window into species that are extinct and their relationships to modern-day life-forms.”