To colour or not to colour: Colour patterns and pigments in Invertebrates from the Palaeozoic of Belgium.

Almost nothing is known about the evolution of shell colour in invertebrates. This is largely due to the ultra-rarity of fossils in which colour patterns and pigments are preserved and immediately visible, and therefore easy to identify, especially when these are hundreds of millions of years old. This hampers our understanding of the role and function of colour in extinct animals, their ecology, mode of life, interactions, development, and evolution. A good example for this ultra-rarity is the Palaeozoic of Belgium, world-renowned for its exquisitely preserved fossils of the Devonian and Carboniferous, enabling to document major transitions in ecosystem dynamics and the evolution of life on Earth (e.g. nekton revolution, terrestrialisation, major climate changes, anoxic events, biodiversity crises) but from which only a few cephalopod, bivalve and gastropod mollusc and brachiopod shells were historically documented preserving coloured traces (mostly by L.-G. de Koninck and P. de Ryckholt, mid to late 19th century). However, recently, it was discovered that many more specimens preserve these traces, in particular those from Tournaisian–Viséan shallow marine reef environments, allowing to investigate its occurrence in different evolutionary lineages of marine invertebrates exactly during one of the main periods of revolution in geologic history. In Brain project B2/P233/P2 nicknamed COLOURINPALAEO financed by Belspo, after gathering all the specimens available in the main Belgian collections, we will use different techniques (multispectral photogrammetry and spectro-imaging) to better visualise the preserved colour patterns and pigments. Furthermore, advanced spectroscopic techniques, namely Raman micro-probe spectroscopy, synchrotron trace elemental mapping and absorption spectroscopy, will be used to identify the chemical signature of the pigments as well as their mode and pathways of preservation. Some of the first results on this multidisciplinary study on a unique set of Belgian fossils will be presented.

RBINS Collection(s), Open Access, Abstract of an Oral Presentation or a Poster