Polyene-based colouration preserved in 12 million-year-old gastropod shells

Polyene pigments represent a major class of pigments in present-day organisms. Their occurrence in fossils has been frequently discussed, but to date no spectroscopic evidence was found. Here, we use in situ Raman microspectroscopy to examine the chemistry of exceptionally well-preserved gastropod shells with colour preservation from the Middle Miocene of the Vienna Basin (Austria, Hungary). Raman signals indicative for the presence of intact, i.e. non-hydrogenated polyene pigments were obtained from the fossil gastropods, thus revealing the first record of intact polyenes in fossils. The observed Raman values are in good agreement with those of unmethylated (non-carotenoid) polyenes. Fossil polyene pigments were detected in representatives of the superfamily Cerithioidea, but not in representatives of other gastropod families with colour preservation found at the same localities. Our results show that Raman spectroscopy represents a valuable tool for the non-destructive screening of rare fossils with colour preservation for the occurrence of polyene pigments.