The brownish-black fossil pigment—a type of melanin called eumelanin—is widespread in the animal kingdom, for example in bird feathers, squid ink, and human hair and skin. The substance has various functions, including protection from the sun and camouflage.

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.

Now Simon and colleagues have used a variety of direct, high-resolution chemical techniques—including scanning electron microscopy and mass spectrometry, which measures the masses of individual ion molecules—to identify eumelanin in the fossilized ink sacs.

Found recently in the floor of a long-gone sea in the