Abstract
Some liquid plant exudates (e.g. resin) can be found preserved in the fossil record. However, due to their high solubility, gums have been assumed to dissolve before fossilisation. The visual appearance of gums (water-soluble polysaccharides) is so similar to other plant exudates, particularly resin, that chemical testing is essential to differentiate them. Remarkably, Welwitschiophyllum leaves from Early Cretaceous, Brazil provide the first chemical confirmation of a preserved gum. This is despite the leaves being exposed to water twice during formation and subsequent weathering of the Crato Formation. The Welwitschiophyllum plant shares the presence of gum ducts inside leaves with its presumed extant relative the gnetalean Welwitschia. This fossil gum presents a chemical signature remarkably similar to the gum in extant Welwitschia and is distinct from those of fossil resins. We show for the first time that a water-soluble plant exudate has been preserved in the fossil record, potentially allowing us to recognise further biomolecules thought to be lost during the fossilisation process.
Highlights
IntroductionSome liquid plant exudates (e.g. resin) can be found preserved in the fossil record. due to their high solubility, gums have been assumed to dissolve before fossilisation
Some liquid plant exudates can be found preserved in the fossil record
Welwitschia is restricted to the Namib Desert in Namibia and Southern Angola and has chemically confirmed gum in both the cone and in abaxial ducts within leaves[24,25]. We investigated this amber-coloured substance inside fossil Welwitschiophyllum leaves to test whether Welwitschiophyllum produced a resin, or a gum like its presumed extant relative Welwitschia, using Fourier-transform infrared spectroscopy (FTIR) and Attenuated total reflectance (ATR) spectroscopy
Summary
Some liquid plant exudates (e.g. resin) can be found preserved in the fossil record. due to their high solubility, gums have been assumed to dissolve before fossilisation. Welwitschiophyllum leaves from Early Cretaceous, Brazil provide the first chemical confirmation of a preserved gum. This is despite the leaves being exposed to water twice during formation and subsequent weathering of the Crato Formation. Due to similarity in physical appearance distinguishing exudates based on chemistry is vital, for example gums and resins are visually similar resulting in these terms being used interchangeably[1] Their chemical definitions are very different (Table 1); resins are composed of lipid-soluble terpenoids[1,2], while gums are complex, highly branched (non-starch) water-soluble polysaccharides[3]. An amber-coloured substance is visible in some of the fossil leaves of Welwitschiophyllum brasiliense Dilcher et al 2005 from the Crato Formation
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