Forests of giant mushroom-the size of trees,
the common place in science fiction and fantasy.
But there was once a time when they were reality.
and fungus did grow to the heights of small trees.
Over 360 million years ago,
a fungus named Prototaxites
towered above its surroundings.
At this point in history,
during the early Devonian period,
trees did not exist yet
let alone huge forests.
And the tallest plants on land
could grow no higher than a man’s waist,
making this giant fungus
the tallest living thing on land.
And so in a role reversal,
the mushroom towered above the other plants,
creating an ecosystem so otherworldly
it would fit perfectly in a science fiction story.
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The discovery of Prototaxites dates all way back to 1843,
but when it was discovered
no one had any idea
the fossils they were looking at
were actually of a giant prehistoric fungus.
And it’s true identity evaded discovery for over a century
with the only really being found out in the 2000s.
This was because it shared qualities
from several different organism groups.
From a distance,
it’s meter-wide trunk made it look like the base of tree.
But under closer inspection,
his body was made up of small tubes that looked a lot like hyphae
which are filaments that make up the body of a fungus.
The first attempts to classify the new fossils
concluded that it was a peculiar ancient conifer,
the fossilized while rotting,
and so was covered in fungus,
which would explain why it has features from both groups.
However, this theory was quickly swept aside
and it was later assumed that Prototaxites were large marine algae.
And despite the overwhelming evidence that the organism grew on land,
this version of Prototaxites as a marine plant
was the most popular view of the large tree fugues
for over a century.
Until as recently as 2001,
when the specimens were re-examined,
and based on its internal structure,
it was finally hypothesize that
it may actually be a giant ancient fungus,
although there was no conclusive proof.
However, with modern technology,
there was now a way that this could be found out.
By studying their carbon isotopes,
specifically the ratios between two common forms of carbon,
carbon 12 and carbon 13.
All plants absorb in metabolized
carbon dioxide from the air,
which means that their carbon ratios tend to be
pretty consistent with the atmosphere of which they live in.
And because all the plants found across a given ecosystem
are getting their carbon from the same source,
all of their ratios will be consistent with each other as well.
However, organisms that get their carbon from their food,
然而 从食物中获取碳的生物 比如动物
like animals tend to look like whatever they eat,
and so their ratios can vary wildly
depending on their diet.
A long time ago, fungus were classified as plants.
However, it is now known
they are actually more closely related to animals,
and consume their food rather than making it for themselves like animals.
even though they chemically absorb their food rather than mechanically digested.
This still means that they will have carbon isotope ratios
that will vary depending on the food they are eating.
The carbon of Prototaxites were studied
and they were found to vary wildly
even among fungus discovered from the same region,
which showed the Prototaxites
must have got some of his food from its surroundings
and not from the air, like a plant would have.
Therefore must have been a fungus.
Their body didn’t have the classic mushroom shape of many modern fungus,
And instead, their featureless tree-trunk-like body
would’ve towered 6 meters off of the ground on average.
With one very large specimen almost reaching 9 meters.
So compared with modern trees this isn’t that tall.
But for the time in the Devonian period
between 420 to 360 million years ago,
they were the largest organisms on land.
The Devonian was a transitional period
when land dwelling creatures and plants
had only very recently descended from aquatic ancestors.
And it was still a whole thing
to solve the problems of living on land.
This meant that the environment that surrounded these large fungus
would have still been sparsely populated.
And the plants that did inhabit the region
would have been primitive like mosses, lichen, liverworts
应该是藓类 地衣 苔类等远古植物
and a strange new extinct group of plants called Cooksonia.
They could grow no larger than a meter at all.
So the Devonian landscape would have been incredibly strange,
but also raises an important question.
Modern day forests contain a large amount of large animals
and plant life to feed on,
and mushrooms that feed off of these environments
are much smaller in comparison.
So how was such a large fungus able to absorb enough food
if all the other organisms in its ecosystem was so much smaller.
In the majority of cases,
the bit of a fungus that sticks out of the ground
is actually only the fruiting part
that is used to spread their spores,
technically known as the sporophore.
And all of the eating is actually done underground
in a network of roots known as mycelium
that consume the energy from their environment.
It would have been possible for Prototaxites
to gather enough food as a normal fungus
by just having a vast and far reaching network of roots under the ground.
Some modern mushrooms like the honey mushroom,
have incredibly far reaching roots.
In fact one member of the species in Oregon
measures almost 2½ miles across.
This means they are able to absorb in
a massive amount of nutrients in food
that could support large structures like Prototaxites.
However, a lot of these modern giant fugues
tend to still have small fruiting bodies.
So why did Prototaxites grow to be so tall?
Well, as the sporophore is used to spread spores,
the taller it is, the further the spores will spread.
And the greater chance they will have been caught in the wind
and spreading even further.
However, large structures take a long time to grow,
and a giant soft body fungus
is a very easy target for large animals.
During the Devonian period, like plants,
animals were also only just starting to conquer the land.
And at the time of Prototaxites,
the world was only occupied by small animals like velvet worms
and some arthropods like ancient scorpions and millipedes.
Although there may have been some semi-aquatic amphibian ancestors
that occasionally waddled across the land,
there were no permanent vertebrate land dwellers at this time
and no permanent land residents larger than your hand.
Because the Devonian had no large animals,
Prototaxites had the luxury of being able to use
a lot of resources into getting very large.
However in the case of modern fungus,
because they are faced with the danger of being eaten
by a large animal.
They have put their eggs in multiple baskets.
This may also be the reason why Prototaxites went to extinct.
Some fossils have been found with mazes of holes through them,
with fungus regrowing into the open spaces and
many scientists believe that
these holes were made by Devonian era creatures,
burrowing into these large structures for food or shelter.
Prototaxites enjoyed a sparsely populated planet for a long time,
but this would change by the end of the Devonian
when animals did start to get larger
as single trees turned into forests
and the ecosystem started to get more complex
and Prototaxites may have been ill equipped for this new world
and so went extinct at the end of the Devonian period about 360 million years ago.
Some researchers have believed that
the reason that Prototaxites was able to get so large
was actually because they were able to photosynthesize
and wanting no more fungus but instead a lichen.
Lichen are fungus, however they get all or some of their energy
through a symbiotic relationship with algae cells contained within their body.
The algae photosynthesize and expel waste
that the fungus feeds on,
meaning that lichen are capable of a sort of quasi-photosynthesis.
So they may have been able to photosynthesise,
and so in a world predating trees
they may have filled a similar niche to a tree,
and would explain how
they were able to survive in an environment
that was very barren by today’s standards.
However for the time being,
that doesn’t seem to be a reliable way
of finding out if these giant fungus were lichens.
A more research will be needed to find out.
So the ancient mega fungus went extinct
as the bizarre early land ecosystems of the Devonian
was swept away for the more complex forests of the Carboniferous.
For Prototaxites and the strange ecosystem that it belonged to
shows how the ancient earth can sometimes be stranger than fiction.
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Forests of giant mushroom-the size of trees,