Labile biomolecules, such as carbohydrates and fatty acids, are rarely preserved in the pre-Quaternary geological record and were traditionally thought to play a nonsupportive role in the preservation of morphological structures during the process of fossilization. We document the in situ preservation of polysaccharides and cutin acids in late Paleocene–early Eocene (approximately 60 Ma) three-dimensionally preserved Metasequoia leaves from Ellesmere Island, Nunavut, in the Canadian Arctic Archipelago. In addition to abundant polysaccharides, cutin-derived fatty acids are effectively detected with a modified version of the online pyrolysis–gas chromatography/mass spectrometry technique that uses tetramethylammonium hyroxide. These biomolecules are the oldest of these types of biomolecules so far documented in the fossil record. Scanning electron microscopy observations of transverse sections of the fossil Metasequoia leaf tissues indicate a layered cuticle overlaying the epidermal cells and amorphous cell walls, suggesting these tissues are the likely sources for the preserved cutin acids and cellulose polysaccha-rides, respectively. We infer that the preservation of these chemically reactive biomolecules in these plant tissues was enhanced by both physical entrapment and chemical bonding of these labile molecules to other structural biopolymers, suggesting a significant role for these labile bio-molecules in the fossilization and preservation of three-dimensional leaf tissues.
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