London | Scientists have identified the oldest fossil of any land-dwelling organism yet found an early type of fungus from 440 million years ago which likely kick-started the process of rot and soil formation, encouraging the growth and diversification of life on land. This early pioneer, known as Tortotubus, displays a structure similar to one found in some modern fungi, which likely enabled it to store and transport nutrients through the process of decomposition. Although it cannot be said to be the first organism to have lived on land, it is the oldest fossil of a terrestrial organism yet found, researchers said.
During the period when this organism existed, life was almost entirely restricted to the oceans – nothing more complex than simple mossy and lichen-like plants had yet evolved on the land, said Martin Smith, who conducted the research at the University of Cambridge in UK. But before there could be flowering plants or trees, or the animals that depend on them, the processes of rot and soil formation needed to be established, said Smith, who is now at Durham University in UK.
Researchers attempted to reconstruct the method of growth for two types of fossils that were first identified in 1980s. The fossils had been thought to be parts of two different organisms, but by identifying other fossils with ‘in-between’ forms, researchers were able to show that they represented parts of a single organism at different stages of growth. The fossils represent mycelium – the root-like filaments that fungi use to extract nutrients from soil. It is difficult to pinpoint exactly when life first migrated from the seas to the land, but it is generally agreed that the transition started early in the Palaeozoic era, between 500 and 450 million years ago, researchers said. But before any complex forms of life could live on land, there needed to be nutrients there to support them.
Fungi played a key role in the move to land, since by kick-starting the rotting process, a layer of fertile soil could eventually be built up, enabling plants with root systems to establish themselves, which in turn could support animal life. Smith found that Tortotubus had a cord-like structure, similar to that of some modern fungi, in which the main filament sends out primary and secondary branches that stick back onto the main filament, eventually enveloping it. This cord-like structure is often seen in land-based organisms, allowing them to spread out and colonise surfaces.
In modern fungi, the structure is associated with the decomposition of matter, allowing a fungus colony to move nutrients to where they are needed. In contrast with early plants, which lacked roots and therefore had limited interaction with activity beneath the surface, fungi played an important role in stabilising sediment, encouraging weathering and forming soils.
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