After examining the evolutionary history of fungi, an international group of scientists has concluded that these organisms first appeared between 900 million and 1.4 billion years ago, far earlier than scientists had believed. This suggests that fungi were thriving on Earth hundreds of millions of years before plants began to grow. The results, published open access in Nature Ecology & Evolution, were made possible through advanced analytical methods and new evolutionary models that combine several dating techniques.
The research brought together specialists from multiple countries and fields, including evolutionary biologist Eduard Ocaña, a Ramon y Cajal researcher at the Universitat Oberta de Catalunya (UOC).
"As a group, fungi are much older than previously imagined. It's highly likely that they were already around over a billion years ago, making them one of the oldest major groups of eukaryotes," said Ocaña. This means that fungi (a kingdom including mushrooms, moulds and single-cell organisms such as yeasts) predate both animals (which are thought to have arisen about 600 million years ago) and multicellular land plants (around 500 million years ago).
A revised timeline for the origins of life
Unlike plants and animals, fungi rarely leave behind fossils because of their soft, thread-like structure. With so few preserved remains, scientists have long struggled to piece together their evolutionary story. To overcome this challenge, the researchers used a combination of three complementary sources: the limited number of known fungal fossils, the genomic sequences of more than a hundred species, and data on horizontal gene transfers -- an unusual but revealing process that turned out to be essential for the analysis.
Horizontal gene transfer occurs when a gene moves from one species to another. "When a gene jumps from one organism to another, that tells us that the two existed at the same time. This enables us to establish relative timelines, because any relative of the donor lineage must necessarily be older than any descendant of the lineage that received the gene," explained Ocaña. By combining evidence from these genetic exchanges with other molecular dating tools and high-speed computational models, the team generated a far more accurate and detailed evolutionary timeline for more than 100 species of fungi.
Fungi: the first pioneers of life on land
The findings go beyond pinpointing ancient dates. They reshape our understanding of Earth's earliest terrestrial ecosystems, which are poorly represented in the fossil record. According to Ocaña, "our findings show that fungi were already present on land environments at least 800 million years ago and had ecological interactions with the ancestors of multicellular land plants, although we're currently unsure about the degree of complexity of these interactions. These ancestors probably shared similarities with the green algae groups that are evolutionarily closest to multicellular land plants, some of whose members have some degree of adaptability to non-aquatic environments."
Modern fungi form symbiotic partnerships with most plants, supplying them with nutrients in exchange for carbohydrates. These ancient relationships, called mycorrhizae, may date back to some of the earliest life on land. Long before complex plants appeared, fungi may have helped algae and primitive plants adjust to terrestrial conditions while gaining new energy sources in return. "If we accept that fungi were instrumental in helping plants colonize the Earth, our theory is that this partnership may have started much earlier than previously thought, in environments similar to biological soil crusts or the microbial mats that we still have today," said Ocaña, who is affiliated with the UOC eHealth Centre and the UOC-TECH Centre.
Reimagining a once "empty" Earth
The traditional view of early Earth portrays a barren planet until plants appeared about 500 million years ago. This study challenges that idea. The new evidence suggests that fungi had already been active for hundreds of millions of years, interacting with early life forms and transforming the landscape. By breaking down minerals, releasing nutrients, and helping to create the first soils, these ancient fungi played a key role in making Earth a more hospitable place for future life.
This discovery, which relied on close collaboration between experts in evolution, paleontology, and molecular biology, also highlights the importance of cross-disciplinary innovation. "The idea originated from an innovative tool developed by Dr Gergely J. Szöllősi's Hungarian group, of which I was a member when I was doing my postdoctoral research. These findings wouldn't have been possible without this collaboration or the contributions made by researchers from Hungary, England, Japan and Catalonia," said Ocaña.
Opening new paths for research
The team now hopes to apply its approach to other branches of complex life to refine our understanding of evolution as a whole. "Fungi were a great subject of study, because the scarcity of fossil records meant that our approach provided significant added value. The next challenge is to extend these techniques to all eukaryotes to develop a much finer molecular clock for all complex life," Ocaña said.
Ocaña's research as a Junior Leader postdoctoral fellow, supported by the "la Caixa" Foundation, forms part of the UOC's broader initiatives in digital sustainability, planetary well-being, and health innovation, contributing to the UN Sustainable Development Goals (SDG 15: Life on Land).
