The fossilized ink sac of an ancient cephalopod—the group of tentacled invertebrates that includes today’s octopi, squid, and cuttlefish—still holds some of the ink pigment, a new study suggests. Researchers unearthed the 30-millimeter-long fossil (above) from 162-million-year-old rocks in the southern United Kingdom, about 40 kilometers east of Bristol. Images the scientists took with a scanning electron microscope reveal tiny, nearly spherical structures that are similar in size to structures in the ink of the modern-day cuttlefish (Sepia officinalis). But that physical similarity doesn’t prove the pigment in those structures is intact because minerals could have replaced the original particles. So the researchers conducted a variety of chemical tests, including placing samples of material scraped from the fossil in a solution that typically breaks down melanin pigments. In this case, the reaction generated two substances found only in eumelanin, a brownish-black form of the pigment that is also found in the ink of today’s cephalopods, the researchers report online today in the Proceedings of the National Academy of Sciences. The new findings may help scientists identify eumelanin or its remnants in other fossils, such as feathers, scales, or skin—which may, in turn, shed light on the diverse roles of pigments in ancient organisms.
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