AbstractMelanin is the most common pigment in vertebrates with two main forms, black melanin (eumelanin) and rufous red melanin (pheomelanin). This pigment is known to preserve chemically over geological time scales, over 100s of millions of years, allowing the reconstruction of aspects of integumentary colouration of fossils to be done. However, the chemical changes that eumelanin incurs during fossilization, including occasional secondary incorporation of sulfur, are still not fully understood. This has the potential of introducing a level of uncertainty in colour reconstructions.
In this project, I aim to investigate the influence of geothermal gradients and the depositional environment (with focus on the presence of sulfur species) on the chemical structure of eumelanin. This was done by analysing a comprehensive collection of fossil cephalopod ink, straddling a wide spectrum of ages (20 – 300 million years), locations, and burial history. For comparison, freshly extracted ink was artificially matured under different conditions (temperature and pressure) as well as with different sulfur species (elemental sulfur and a source of sulfide) to compare its chemistry with sulfur bearing pheomelanin. Samples were analysed with ToF-SIMS and FTIR, and comparatively analysed multivariate framework (PCA).
The PCA plots of the ToF-SIMS data verifies that maturation history has the greatest influence on eumelanin alteration. Comparative PCA analysis of FTIR data were used here for the first time on melanin and shows great promise for evaluating chemical alterations during fossilization in concordance with ToF-SIMS. FTIR elucidates the specific alteration of progressive dehydration and loss of carboxyl groups with increasing temperature. Lastly, artificially matured melanin with sulfur species yields thiophenes, but no moieties diagnostic of pheomelanin (thiazines/thiazoles).
|Date of Award||27 Mar 2019|
|Supervisor||Jakob Vinther (Supervisor)|