Scientists have unearthed fossilized fungi in the remote Northwest Territories of the Canadian Arctic dating back to one billion years, in a discovery that could reshape our understanding of how life first arrived on land from the oceans.
Fungi, the “Hidden Kingdom,” are not plants. Living things are organized for study into large, basic groups called kingdoms. Fungi were listed in the Plant Kingdom for many years. Then scientists learned that fungi show a closer relation to animals, but are unique and separate life forms. Most fungi build their cell walls out of chitin. This is the same material as the hard outer shells of insects and other arthropods. Plants do not make chitin.
Scientists have identified about 120,000 species of fungi so far, reports Carl Zimmer in The New York Times, “but estimate there are as many as 3.3 million species in all. By comparison, all living mammals comprise fewer than 6,400 species. The success of fungi results largely from their unique way of feeding. Rather than absorbing sunlight like plants or devouring other organisms like animals, fungi spew out powerful enzymes. These break down surrounding cells or even rock, which the fungi slurp up.”
For decades, the earliest known fungi—organisms such as mushrooms, mould and yeast—was thought to have appeared on earth around half a billion years ago. But the recent fossil specimens unearthed in Canada and analyzed using the latest dating technology appear to push back fungi’s arrival to the earliest reaches of life on land. Analysis of the rocks showed that these organisms, whatever they were, had fossilized a billion years ago in an estuary, where a river flowed into a sea (photo below courtesy Dr Robert Rainbird)
On an expedition in 2017, Robert Rainbird, a research scientist at the Geological Survey of Canada, Corentin Loron, a PhD candidate from the University of Liege, Belgium, and their colleagues discovered some peculiar fossils in the rocks. They were composed of spore-like spheres, often joined to long filaments that sprouted T-shaped branches — the kind of shapes found today in fungi.
Rainbird noticed black flecks on a piece of shale. He knew that sometimes flecks like these turn out to be microscopic fossils. “I thought, ‘I should grab some of this stuff, because it looks juicy,’” he said.
Loron examined the microfossils to determine the chemical composition of their cells. They found the presence of chitin—a fibrous substance that forms on fungal cell walls—and examined the age of the rock the fossils were found in by its ratio of radioactive elements. They concluded the microfossils were between 900 million and one billion years old.
Loron said the finding was significant because in the “tree of life”, fungi are part of the same umbrella group of organisms—known as Eukaryotes—as plants and animals. “This means that if fungi are already present around 900-1000 million years ago, so should animals have been,” he told AFP. “This is reshaping our vision of the world because those groups are still present today. Therefore, this distant past, although very different from today, may have been much more ‘modern’ than we thought.”
Fungi are among the most abundant organisms on the planet and are the third largest contributor to global biomass after plants and bacteria. They are six times heavier than the mass of all animals combined—including humans.
The study was published in the journal Nature.
Image credit: USU Herbarium