110-Million-Year-Old Fossilized Plant Gum Found
Paleontologists in Brazil have found thin bands of fossil gum — the first occurrence in the fossil record — inside 110-million-year-old (Cretaceous period) fossilized leaves of the extinct plant Welwitschiophyllum brasiliense. The discovery of fossilized plant gum is unusual because of its solubility in water.
A wide variety of plants produce fluid exudates e.g. resins and gums, with each group differing in chemical definitions.
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.
However, their chemical definitions are very different; resins are composed of lipid-soluble terpenoids, while gums are complex, highly branched (non-starch) water-soluble polysaccharides.
Differences between gum and resin can also be seen in the functional roles within the plant.
The main roles of resins are to respond to wounding, as a defense against pathogens and to dissuade herbivory by insects and other organisms.
Gum is involved in food storage, structural support, and also for wound sealing, but there is no common role across species.
Further confusion arises as some plants, e.g. Boswellia and Commiphora species, even produce exudates with a mixture of polysaccharide and resin components (the gum resins myrrh and frankincense, respectively).
Until now only fossilized plant resin (ambers) and latex filaments have been reported preserved in the fossil record.
While the fossilization of fluid exudates might seem unlikely, the fossilization of resin is relatively common, and extends back some 320 million years to the Carboniferous period, but chemically confirmed gums have never been reported.
“Our discovery overturns the basic assumption that plant gums cannot be preserved in the fossil record,” said lead author Dr. Emily Roberts, a researcher in the School of the Environment, Geography and Geosciences at the University of Portsmouth and the Department of Palaeontology at the University of Vienna.
“It has opened our eyes to the fact that other plant chemicals may also be preserved — we can no longer just make assumptions. When we first tested the gum I was astonished that we were confirming something that was thought to be impossible — it just goes to show that fossil plants can surprise us.”
Using Fourier-transform infrared spectroscopy (FTIR) and attenuated total reflectance (ATR) spectroscopy, Dr. Roberts and colleagues analyzed the amber-colored substance inside Welwitschiophyllum brasiliense leaves from Crato Formation, Brazil.
The chemical spectrum of this substance clearly differed from those of ambers and resins, but resembled spectra of plant gum.
Welwitschiophyllum brasiliense is considered a relative of Welwitschia mirabilis, one of the oldest and most enigmatic plants in existence.
Today, Welwitschia mirabilis can be found only in the Namib Desert in Namibia and Southern Angola and has chemically confirmed gum in both the cone and in abaxial ducts within leaves.
“Our findings confirm that the Welwitschia mirabilis plant found in Africa today produces a gum similar to a plant growing 110 million years ago in Brazil,” said co-author Professor David Martill, also from the School of the Environmental Geography and Geosciences at the University of Portsmouth.
“Welwitschia mirabilis is one of life’s survivors, thriving in one of the harshest environments on earth for over 120 million years.”
“This discovery is extremely exciting, especially when put into the context of these two continents of Africa and South America, being one during the Cretaceous period.”
The results were published in the journal Scientific Reports.
E.A. Roberts et al. Cretaceous gnetalean yields first preserved plant gum. Sci Rep 10, 3401; doi: 10.1038/s41598-020-60211-2