Mr. Arindam ROY Department of Earth Sciences, HKU
The preservation of the pigment melanin (embedded in tiny vesicles called melanosomes) in fossilised soft tissues permits the reconstruction of melanin-based colouration and patterning in long extinct vertebrates. This has further created unique opportunities to articulate and test hypotheses on life history traits, ecology, behavioural strategies, ancient ecosystems and make predictions supported by strong empirical evidence. However, the scientific arena of ‘palaeocolour research’ is still in a nascent stage with considerable potential for expansion and refinement. The key issues with current efforts involve (1) a lack of contextualisation of various methods, (2) incomplete preservation in fossils, (3) poor understanding of the diagenetic chemistry of melanin and other pigment molecules, and (4) more accurate statistical analyses for palaeocolour prediction. These very issues become the research foci in my PhD thesis. In the first chapter, I provide a comprehensive review of pigmentary systems, colour mechanisms in extant and fossil amniotes and develop a new synthetic workflow. The workflow collates and contextualises the current methods, making it robust, highly repeatable, and less liable to be affected by taphonomic bias. In the second chapter, I compile a large database of melanosome shapes in vertebrates and apply machine learning algorithms to improve the accuracy of fossil colour prediction. This new approach has the potential to predict melanin-based palaeocolour with enhanced accuracy. In chapters 3 and 4, I also investigate the effects of diagenesis on melanin, carotenoid and psittacofulvin pigments by subjecting them to a novel maturation setup called ‘sediment encased maturation’ which closely mimics natural diagenesis to generate ‘synthetic fossils’. I also find that beyond 250°C, melanin forms highly stable crosslinks that lead to its high preservation potential whereas carotenoids and psittacofulvins rapidly degrade to their carbon skeletons and mobilise through the sediment pores at temperatures as low as 100–150°C, thereby making them poorly fossilisable.
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