Sprecher
Beschreibung
Leaf epicuticular waxes form the outermost protective layer of leaves and reflect adaptations to environmental conditions. Their morphology and chemistry is usually not well preserved in the fossil record but can be under specific circumstances, providing information for paleoclimate reconstruction and taphonomic histories of leaves in lignites. Whitish fossil layers on Eocene leaves have been interpreted as preserved epicuticular waxes, although an alternative hypothesis suggested secondary ex situ accumulation of waxes derived from the surrounding lignite. Here, we investigate the late Eocene leaves of the fossil-species Eotrigonobalanus furcinervis and Daphnogene cinnamomifolia, both exhibiting whitish wax layers. (1) Scanning electron microscopy (SEM) revealed taxon-specific wax morphologies. E. furcinervis shows vertically oriented non-entire platelets, whereas D. cinnamomifolia exhibits horizontally stacked hollow platelets. Recrystallization experiments demonstrated differences in platelet shape and size, with 1–2 µm valley-shaped platelets in E. furcinervis and 3–7 µm medially ridged valley platelets in D. cinnamomifolia. (2) Preliminary gas chromatography-mass spectrometry (GC-MS) analyses indicate differences in chemical composition, with dominant long-chain C28 and C30 fatty acids in E. furcinervis and C28 and C30 alcohols in D. cinnamomifolia. The observed taxon-specific morphological and chemical patterns disagree with ex situ wax accumulation from the surrounding lignite and instead support in situ preservation of modified but taxon-specific epicuticular wax structures. Furthermore, examination of more than 1500 fossil leaves revealed significantly stronger whitish layer formation on abaxial leaf surfaces, consistent with the in situ hypothesis. These findings highlight the potential of fossil wax preservation as a proxy for paleobotanical and paleoenvironmental reconstructions.