A possible fungal fossil extends the record by over half a billion years

Until 2019 the oldest unambiguous fungal fossils came from the middle Palaeozoic, about 450 million years ago. That May, Corentin Loron and colleagues published in Nature a description of multicellular organic-walled microfossils preserved in shale of the Grassy Bay Formation in Arctic Canada. The bed dates to 1,010–890 million years ago — more than half a billion years earlier.

Establishing that something so small and so old is a fungus takes more than a photograph. The authors combined three independent lines of evidence: morphology (branching hypha-like filaments with septa, and spore-like structures), the ultrastructure of the cell wall, and spectroscopic analysis pointing to the presence of chitin. Chitin builds fungal cell walls and does not occur in plants, so its signal is the decisive argument here.

The consequence reaches beyond the fungal kingdom. Fungi belong to Opisthokonta, the group that also contains animals and their single-celled relatives. If fungi already existed a billion years ago, the minimum date for that branch moves with them. The result also agrees with molecular clocks, which had long pointed to dates older than the fossil record allowed — and the gap between those two methods was one of the more durable arguments in the field.

Caution is warranted, and the authors do not hide it. The affinity of a microfossil is established by inference from characters, not by observing a living organism. A chemical signal a billion years old comes from matter that has been through a long geological history. The paper offers the best available interpretation rather than a closed proof, and it should be read that way.

What the evidence actually shows

The finding concerns the oldest proposed fungal fossil, not the date when the entire kingdom originated. Ourasphaira giraldae comes from shales of the Grassy Bay Formation in Arctic Canada, dated to about 1.0–0.9 billion years ago. The microfossils have multicellular filaments branching at right angles, terminal spherical structures, and two-layered walls. Spectroscopy produced a signal consistent with chitin. Taken together, these features led the authors to place the organism within the fungal total group and extended the direct record by more than 500 million years relative to earlier, widely accepted specimens. Any extremely old microfossil still demands caution: chitin is not exclusive to fungi, and similar shapes can evolve in other eukaryotes. This is a strong interpretation based on several converging lines of evidence, not preserved DNA or a secure position within a modern fungal lineage.