An international team of researchers has found the microscopic fungal filaments and mycelium-like structures in dolomitic shale from the Democratic Republic of Congo. The microfossils are at least 715 million years old (Neoproterozoic Era), making them 255 million years older than the next oldest fungi fossil.
“These ancient rocks formed in a lagoon or coastal lake environment,” said Professor Steeve Bonneville, a scientist at the Université Libre de Bruxelles, Belgium.
“The presence of fungi in this transitional area between water and land leads us to believe that these microscopic mushrooms were important partners of the first plants that colonized the Earth’s surface around 500 million years ago.”
Using multiple molecular analysis techniques, such as synchrotron radiation spectroscopy, μ-Raman confocal microscopy, fluorescence microscopy, and electron microscopy, Professor Bonneville and colleagues demonstrated the presence of chitin — a very tough compound found in the cell walls of fungi — in the Neoproterozoic fungal microfossils.
The researchers also demonstrated that the organisms were eukaryotes, i.e. their cells had a nucleus.
“We document dark, nontranslucide, cylindrical filaments typically between 3.5 and 11.5 μm in width, extending over several hundreds of micrometers in length,” they said.
“These filaments sometimes evolve into dense interconnected networks of 500 μm in diameter.”
“In these mycelium-like structures, filaments have multiple-order, high-angle branching and, possibly, anastomosing filaments, common features of fungal networks yet rare for prokaryotes.”
The filaments for living and fossil fungi range from 2 to over 20 μm in width.
The size of the Neoproterozoic fossil filaments observed by the team fits well with fungal dimensions.
“This is a major discovery, and one that prompts us to reconsider our timeline of the evolution of organisms on Earth,” Professor Bonneville said.
“The next step will be to look further back in time, in even more ancient rocks, for evidence of those microorganisms that are truly at the origins of the animal kingdom.”
The findings were published in a paper in the journal Science Advances.
S. Bonneville et al. 2020. Molecular identification of fungi microfossils in a Neoproterozoic shale rock. Science Advances 6 (4): eaax7599; doi: 10.1126/sciadv.aax7599