PATTERNS OF EUMELANIN PRESERVATION IN FOSSILIZED COLEOID INK SACS

Understanding the mechanisms behind the preservation of pigment in the fossil record has profound implications for our knowledge of ancient ecosystems and the evolution of animal coloration. Despite significant advancements in paleobiology, there is a critical gap in understanding the factors that influence the preservation of pigment (i.e., eumelanin) in the ink sacs of coleoid cephalopods. We address this gap by investigating the role of taphonomic biases in the preservation of eumelanin. We evaluated a subset of the Yale Peabody Museum’s fossil coleoids with preserved ink sacs, largely from the Carboniferous and Jurassic periods, via SEM imaging of the preserved ink sac material. Imaging revealed robust eumelanin globules preserved on the microscale for every sample. Compared to a sample of modern powdered squid ink, fossilized ink included eumelanin granules of the same size and shape, with some instances of recrystallization and/or diagenesis reflecting thermal maturation. Chemical analysis (energy-dispersive x-ray spectroscopy) revealed the presence of both organic material and phosphate in some of the samples, indicating that apatite formed during diagenesis. In order to get a more holistic view of the factors influencing ink sac preservation, we also compiled an extensive dataset of fossil coleoids (n=185) from the literature, testing for associations between lithology, age, depositional environment, ink presence, and preservation type. Our preliminary results suggest that ink sac preservation requires associated eumelanin and that the survival of structural details of squid ink is favored in localities with low thermal alteration.