DECODING THE WHITISH LAYER ON CENOZOIC FOSSIL LEAVES IN LIGNITES—A PECULIAR TYPE OF WAX PRESERVATION

Abstract The whitish layer on fossil leaves from various Cenozoic localities has aroused the interest of paleobotanists due to its similarity to the white wax layers on many extant plants. The lack of detailed studies demonstrating the nature of whitish layers on fossils was our motivation to investigate their composition. In the present study, samples of whitish and yellowish fossil leaves representing three genera, from four different stratigraphic levels of lignitic deposits, were investigated. For comparison, extant leaves of the assumed nearest living relatives to the fossil species were also investigated. Initial tests were conducted to ascertain the presence of wax: a melting temperature below 80°C; solubility in chloroform; and a hydrophobic character. Analyses were performed on whitish coatings of fossil leaves and surrounding coaly sediment. Gas chromatography results demonstrated that all fossil leaves contained the typical aliphatic wax components. Furthermore, high-resolution scanning electron microscopy and EDX element analysis illustrated similarities between the morphology of the carbon-dominated whitish layers on fossil leaves and epicuticular wax on extant leaves. This study demonstrated well-preserved wax biomarkers on Cenozoic fossils but revealed certain differences between the wax compositions of fossil and fresh leaves of extant species, in particular greater heterogeneity in the composition of fossil waxes.