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FOSSIL COLOUR Report Summary

Project ID: 618598
Funded under: FP7-PEOPLE
Country: Ireland


CIG Periodic Report 618598 ‘Fossil Colour’ – Publishable summary
Objectives. This project aims to resolve important aspects of the fossil record of animal coloration, thereby enhancing our ability to infer original coloration and its evolution and functions in fossil insects and theropods. The research will employ a powerful three-fold approach combining decay experiments, maturation experiments and fossil analysis to the study of the taphonomy of key pigments (melanins, carotenoids and pterins) and colour-producing structures in insects and feathers. Experiments will simulate the processes of autolytic decay and deep burial, and will elucidate, for the first time, the chemical steps involved in the alteration of key pigments in insects and feathers during decay and diagenesis, and the extent to which this process, and alteration of structural colours, is impacted by sedimentological and taxonomic factors. The experimental results will ground truth data obtained from comprehensive analysis of diverse fossil insects and feathers from the Cenozoic and Mesozoic, facilitating the first systematic attempt to map preservation of colour in fossil insects and feathers through deep time.
Work performed. A new research laboratory, including key links with administrative and technical support staff, as well as collaborators in other institutes, has been established. Training in all relevant safety procedures and analytical techniques has been completed. One comprehensive series of maturation experiments on structurally coloured insects has been completed. Decay of structural colours has been assessed using FESEM-EDS, TEM and microspectrophotometry. One pilot series of 2-month long decay experiments on pigmented insects is complete and a second, longer series, of 6-month long decay experiments is in progress (and will conclude in September 2016). Decay of pigments has been assessed using FESEM-EDS, EPMA, synchrotron-XRF and synchrotron-XANES, GC-MS, LC-MS and microspectrophotometry. One comprehensive series of maturation experiments on pigmented insects has been completed, and a second is planned for November 2016. Results have been analysed using SEM-EDS, EPMA, synchrotron-XRF and synchrotron-XANES and EXAFS. The ultrastructure and chemistry of a broad range of structurally coloured fossil insects is in progress. The focus thus far has been on Pleistocene insects; 22 specimens have been analysed using FE-SEM and microspectrophotometry and synchrotron-SAXS. TEM analysis is in progress.
The inorganic chemistry of a broad range of fossil insects with colour patterning is in progress. 15 specimens have been analysed thus far; further specimens will be analysed in spring 2017. The inorganic chemistry of a 55 modern insect taxa with colour patterning has been analysed. Taphonomic models are in development. The results of the research have been disseminated extensively. Six papers has already been published (including two in Science and one in Current Biology), two papers are in review, three papers are in preparation. The work has been presented at six conference presentations. The PI has developed a new teaching curriculum at UCC. A dynamic outreach program has been developed, including a website (, interactive lectures, public exhibits, and undergraduate internships.

Results. The taphonomy of structural colours in fossil insects. Maturation experiments using modern structurally coloured beetles, flies and bugs shows that there are both taxonomic and environmental controls on alteration of insect structural colours during diagenesis, relating primarily to cuticle thickness and environmental pH. Organic geochemical analysis reveals that maturation at high temperatures generates maillard reaction products from the chitin-protein complex in the cuticle. Changes in colour during maturation are caused by decreased abundance of cuticular proteins and associated amino acids, not by changes in chitin abundance. The fossil record of 3D photonic crystals. The research has led to the discovery of the first known 3D photonic crystals in the fossil record, and the first hypotheses for their functional evolution, i.e. that they originated as cryptic structures but were later co-opted for use in mating displays. The taphonomy of pigmentary colours in fossil insects – the significance of copper (Cu). Analysis of the spatial distribution of trace elements in patterned cuticles in fossil insects reveal striking spatial partitioning of Cu, an element used as a proxy for colour in other fossils. Maturation experiments, however, show that Cu zonation is sympathetic to original colour patterns only under certain diagenetic conditions. Spatial distributions of other elements, including Na, K, Cl, Mn and Ti, are sympathetic to original colour patterns. This suite of elements allows colour patterns to be reconstructed in fossil insects even where specimens lack visible patterning. The taphonomy of pigmentary colours in fossil insects – the role of decay. Decay experiments on modern insect cuticles show that morphological and chemical decay is more advanced in melanin-poor cuticle regions and during decay in basic media. Melanin-rich cuticle regions are usually associated with high concentrations of Ca and Mn (and sometimes additional elements), but these zonation patterns can be altered by decay. The taphonomy of fossil feathers and feathered dinosaurs. The research formed part of a high-profile paper reporting the discovery of diverse feathered types in an ornithischian dinosaur, suggesting that all dinosaurs may have been feathered. The taphonomy of melanin. We developed the first taphonomic model for the preservation of fossil melanin, and an approach for discriminating between fossil eumelanin and phaeomelanin, thus allowing more accurate reconstructions of fossil colour. Fossil vertebrate colour. We reported the discovery of diverse pigment cell types in a fossil snake, allowing the first reconstructions of carotenoid-based and structural colour in fossil integument.
Expected final results. The expected final results will include publications on the following (in addition to results already published): (a) Trace elements as a proxy for pigmentary colour in insects; (b) experimental taphonomy of pigmented cuticle in insects; (c) experimental taphonomy of structural colour in insects; (d) the chemistry of structural colour in fossil insects.

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