First fungus pushed back half a billion years

A discovery in the cold of the Canadian Arctic has established a new calibration point for the evolution of fungi.

Abundant fossil fungi dating to between 1000 and 900 million years ago have been found preserved in estuarine shale of the Grassy Bay Formation in Northwest Territories. Previous research dated the first unambiguous fossil records of fungi to only 400 or so million years ago. That’s a lazy half a billion years’ difference.

Fungi are crucial components of modern ecosystems and associated with the earliest signs of life on land, but have been absent from the fossil record until the mid-Palaeozoic era.

The new find, by a Belgian, Canadian and US team led by Corentin Loron from the University of Liege, Belgium, dates to the mid-Proterozoic era. 

“As a consequence of their role in biological cycles (such as the degradation of organic matter, symbiosis and phosphate fixation), fungi today have key roles in aquatic and terrestrial ecosystem dynamics; they may have had similar roles in the Proterozoic era,” the authors write in the journal Nature

“Fungi were also part of the early osmotrophic eukaryotic microbial community, which is documented from the Late Palaeoproterozoic or Early Mesoproterozoic eras.”

Loron and colleagues note that several Precambrian microfossils have been tentatively interpreted as fungi in the past 50 years and that a few Proterozoic fossils – notably, parts of the Ediacaran biota – have been compared to lichen-like organisms. 

However, these studies have focused on broad morphological comparisons, they say, and these, in isolation, “cannot fully support a specific affiliation with the fungi”. 

They, thus, took things further in analysing their Canadian find. “The combination of the microfossil morphology, wall ultrastructure and chemistry of these microfossils is consistent with a fungal affinity,” they write. 

“The septate filaments with right-angled branching and terminal spheres may be interpreted as hyphae with terminal spores, similar to the spore-bearing stages of many fungi.”

The microfossil in question is the organic-walled Ourasphaira giraldae. The authors identified septate hyphae – a type of filament typical of fungi – and the presence of chitin in the cell walls of the specimens, determining that its structure is characteristically fungal. 

This represents the earliest presence of chitin – the fibrous substance that forms fungal cell walls – in the geological record. 

Previously, the earliest uncontested fossil fungi are specimens from the 410-million-year-old Rhynie chert of Scotland and arbuscular spores of glomeromycotan fungi from Wisconsin that date to 450 million years ago.  

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