IDENTIFICATION OF ORGANIC PIGMENTS IN MACROFOSSILS: ANALYTICAL CHALLENGES AND RECENT ADVANCES

Fossil quinone pigments (fringelites) have been detected in exceptionally well preserved, purple to violet colored Jurassic and even Triassic crinoids (Blumer, 1960; Wolkenstein et al., 2006). The distinct pink coloration of specimens of the common Jurassic calcareous red alga Solenopora jurassicahas also been attributed to fringelites; however, further analysis led to the discovery and preliminary characterization of unique organic pigments containing the element boron (borolithochromes) (Wolkenstein et al., 2010).

Whereas fossil crinoid pigments could be identified by high-performance liquid chromatography-mass spectrometry (HPLC-MS) in comparison to reference compounds, completely unknown compounds such as the borolithochromes generally cannot be compared to a reference, making their identification much more difficult. Furthermore, direct identification of individual compounds from fossil organisms by conventional nuclear magnetic resonance (NMR) spectroscopy was until recently not possible due to the tiny amounts of extractable organic compounds and the inherently low sensitivity of NMR.

Using the new methodology of microcryoprobe NMR (Molinski, 2010), the chemical structure of isolated borolithochromes now could be fully elucidated, revealing that the fossil red algal pigments are almost unchanged ancient metabolites, which, however, differ fundamentally from those known from present-day red algae. Moreover, analysis of diverse fossil material by HPLC-MS shows that both groups of fossil pigments were much more widespread than previously thought and likely occurred globally in specific Mesozoic crinoids and calcareous red algae.