A newly-discovered, 440-million-year-old fossilized fungus is not only the earliest example of its kingdom ever discovered, but is the oldest fossil of any land-dwelling organism unearthed to date, claims a new study published today in the Botanical Journal of the Linnean Society.

The fossil, which has been identified as Tortotubus, is structurally similar to many modern kinds of fungi and likely could store and transport nutrients through the process of decomposition, lead author Dr. Martin Smith of Durham University and his colleagues explained in a statement.

While the fossilized fungus has not yet been confirmed to have been the first organism found to have lived on land, it is the oldest preserved remains of a terrestrial organism discovered to date, and the authors believe that it played a key role in establishing the foundation for more complex plants, and eventually animals, to exist by starting the process of rot and soil formation.

“During the period when this organism existed, life was almost entirely restricted to the oceans,” said Dr. Smith, who performed his work while at Cambridge University. “Nothing more complex than simple mossy and lichen-like plants had yet evolved on the land. But before there could be flowering plants or trees… the processes of rot and soil formation needed to be established.”

Filling an important gap in the evolution of terrestrial life

While working with several microfossils discovered in Sweden and Scotland, Dr. Smith and his colleagues set out to reconstruct growth methods for two different kind of fossils that were first identified about three decades ago. In doing so, they discovered that what they thought were two different organisms actually represented two growth stages of the same lifeform.

By reconstructing this organism’s growth process, they demonstrated that the fossils represented mycelium, or the root-like filaments used by fungi to extract nutrients from soil. While it is hard to pinpoint exactly when plant life made the transition from water to land, fungi would have been an essential part in this move, as the rotting process it kick-started was vital for fertile soil.

In turn, the fertile soil would have allowed plants with root systems to establish themselves, and ultimately to help support animal life once it developed. Furthermore, the researchers noted that fungi are a key part of the nitrogen cycle, through which nitrates in the soil are gathered by roots and ultimately passed on to animals, by decomposing and converting nitrogen-rich compounds in plant and animal waste and remains back into nitrates so plants can collect them again.

According to Dr. Smith, Tortotubus was found to have a cord-like structure similar to that found in many modern fungi. In this structure, the main filament sends out both primary and secondary branches that stick back onto the main filament and ultimately envelop it. In today’s fungi, these structures are linked to the decomposition of matter, enabling fungal colonies to transport around nutrients and distribute them where they are most needed.

“What we see in this fossil is complex fungal ‘behavior’ in some of the earliest terrestrial ecosystems – contributing to soil formation and kick-starting the process of rotting on land,” he said. “This fossil provides a hint that mushroom-forming fungi may have colonized the land before the first animals left the oceans. It fills an important gap in the evolution of life on land.”

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Image credit: Martin R. Smith/University of Cambridge

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