Sediment-encased pressure-temperature maturation experiments chemically simulate natural diagenesis of melanin

Abstract

Palaeocolour informs the ecology, physiology and behaviour of extinct animals. However, there is room for improvement in palaeocolour reconstructions due to poor understanding of the chemical changes occurring in pigmented soft tissues during fossilisation. Pressure-temperature maturation experiments are key to expanding our knowledge of pigmented soft-tissue preservation. Prior work on melanin has yielded limited insights in highly closed systems due to stable and volatile diagenetic products mixing and obscuring chemical analyses as well as in open systems because of the leaking and loss of samples. To replicate natural fossilisation, modern melanised feathers were encased in a porous bentonite clay matrix and subjected to a next-generation maturation system. Resultant samples closely resemble natural fossils both visually and chemically. Using mass spectrometry, increased crosslinking is identified within the overall melanin polymer alongside predictable loss of volatile nitrogen/sulphur bearing molecular groups with higher maturation temperatures for the first time, chemically simulating natural melanin diagenesis.