A tiny fossil amoeba is helping us to understand how plants first bloomed
Single-celled amoebae were an early form of life on Earth that evolved in the sea. Now scientists have uncovered the earliest ever terrestrial species of an important type known as testate amoebae.
The fossil amoebae were found in ancient Scottish rock dating to 400 million years ago, pushing back the origin of the organisms by hundreds of millions of years. They also help us to understand how plants and animals transitioned from water to land.
Unicellular amoebae are microscopic living organisms made up of just a single cell. Within this
Testate amoebae are a significant component in modern ponds,
They may also have helped plants to
Christine found the species while researching the origin and evolution of soil-dwelling fungi that live in association with plants.
This discovery of these amoebae, now named Palaeoleptochlamys
A partnership between fungi and plants
Known as mycorrhiza, the mutual relationship between fungi and plants is vital for both to survive. While the plants provide the fungi with energy, the fungi supply the plants with water and nutrients.
But the relationship goes deeper than this, as the mycorrhizal network spread out beneath the soil can even be used to pass messages between individual plants, warning each other of hungry arthropods and voracious herbivores.
Christine and her colleagues are using a rock formation known as Rhynie chert to find out when this intimate relationship first started.
This sedimentary rock is found near Aberdeen, Scotland, and contains exceptionally well-persevered fossils of some of the earliest plants and animals to have
'The main purpose of this work was to look at the environment 400 million years ago and to see what kind of organisms you can find in ponds and soil,' explains Christine. 'I work on the relationship with fungi and other organisms, but in this
At the time when the plants were
Located just below the equator in the southern hemisphere, it would have experienced a much warmer climate. The plants that had moved onto land were still small - only around 20
This is not the earliest evidence of land plants, as they are thought to have made the transition at least 470 million years ago, but the Rhynie chert contains the earliest complete terrestrial ecosystem ever discovered. This is down to where the plants were growing and the way in which they were preserved.
'It would have looked a little like a geothermal wetland in Iceland,' explains Paul. 'These plants were growing near hot springs that were flooding the surrounding environment. It is this silica-rich water that covered the ecosystem and preserved the organisms in such detail.'
As the water that submerged the plants cooled the silica was deposited in the form of sinter. This trapped and preserved in exceptional detail not only the plants but also the early animals, fungi and all other associated microorganisms that were living in ponds and soil. This has provided an unusually detailed look into what was happening on land at this early point in time.
This discovery is helping scientists to work out how life on land got started and when the complex, interdependent relationships between plants and microorganisms began. The new fossils support the hypothesis that these testate amoebae transitioned from marine through freshwater environments, eventually
'Life on land goes way back in time, but mostly in the form of bacterial mats,' explains Paul. It is likely that plants and animals made the transition to land at the same time, and that the microbial mats present effectively primed the ground for their arrival.
'One of the enabling factors for the plants would have been the microbial community that was already there,' says Paul.
This suggests that the symbiotic relationships seen today are as ancient as terrestrial plants themselves and may even have been necessary for the transition to occur in the first place.
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