Name: When Giant Fungi Ruled
Uploaded: 2021-05-03T03:26:56.000Z
Duration: 6 min 38 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

420 million years ago, a giant rose along the river banks of what would become North

It feasted on the dead, growing slowly into the largest living thing on land.

This towering colossus wasn't animal, plant, or mineral.

Instead, it belonged to an unlikely group of pioneers that ultimately made life on land

If you're anywhere on land right now -- like, not on a fishing boat or a floating oil rig

-- then all of the life that you see around you is there, because of fungi...

... fungi like the small, unassuming little decomposer known as Tortotubus protuberans.

It's one of the earliest known fungi in the fossil record, dating back 440 million

Tortotubus grew near coastlines and rivers on the supercontinents of Gondwana and Laurentia

-- in regions that would eventually become New York, Saudi Arabia, Sweden, and Scotland.

But back then, life in these places was anything but lush.

On land, signs of life were sparse -- there were bacteria, algae, early plants like liverworts,

and possibly some of the first terrestrial arthropods.

But if it weren't for fungi, things probably would've stayed that way.

Because, even though they weren't very big, early fungi like Tortotubus had a superpower

-- the ability to break down almost anything, using digestive enzymes.

Fungi eat by releasing enzymes that break down organic matter.

This allows them to take the nutrients they need from the material, while helping the

But! These enzymes can be so powerful that they can eat into solid rock.

Given enough time, and some help from erosion, many fungi can weaken rocky earth and eventually

form fertile soil that plants can sink their roots into.

So big, complex life on land -- like vascular plants -- probably wouldn't have been possible

if Tortotubus and its fungal predecessors hadn't prepared the land first.

Once plant life started to spread and diversify on land in the Devonian Period, fungi were

Some scientists think that the first land plants used symbiotic fungi in their roots

to help them gather and transport nutrients.

In fact, most plants still do this today.

If you pull a plant out of the soil, you'll probably see a lot of dirt sticking to little

Those hair-things are actually bundles of nutrient-absorbing tendrils -- called hyphae

-- from fungi living symbiotically with the plant.

And these fungal structures are incredibly important for making arable soil that plants

They help stabilize soil, retain moisture, and hang on to nitrogen.

So without fungi, soil would just be ... non-nutritious dirt.

Despite their starring role in making life on land possible, ancient fungi haven't

That's probably why, back in the 1800s, when paleontologists discovered a fossil that

was eight times taller than the tallest plants of its time, no one expected it to be a fungus.

Geologists first discovered this enormous fossil in 1843, during a coal survey in Gaspé

It was more than 8 meters tall, shaped kind of like a tree trunk.

And it came from a layer of earth that dated back 420 million years, when the Silurian

Period gave way to the Devonian -- a good 20 million years after Tortotubus first appears

And for a long time, researchers were totally stumped by this specimen.

Stumped? Is that supposed to be some kind of tree trunk joke?

The fossil remained unstudied in a museum collection for years before a Canadian paleontologist

named John William Dawson had found more, new specimens in the 1850s, and tried to classify

Dawson thought this thing might be a primitive conifer tree with some sort of fungus growing

So he named it Prototaxites, which means “first yew,” after the tree he thought it most

Then, in 1872, botanist William Carruthers wrote a paper saying that Prototaxites couldn't

He said it was probably a giant mound of algae, possibly kelp.

And, to his credit, English botanist Arthur Harry Church also studied Prototaxites in

1919, and he said it probably was a fungus.

But nobody really paid much attention to him at the time which is...too bad.

So, based on Carruthers' findings, Prototaxites was filed under “probably weird algae”

Until the 1990s, when Francis Hueber, a curator at the Smithsonian Museum of Natural History,

And he focused on a feature of Prototaxites that had long puzzled scientists: these strange

They looked kind of like growth rings, like what you find in modern trees.

But the rings in Prototaxites were lopsided and not always concentric.

So Hueber examined them under the microscope and found long, tube-shaped cells that were

similar to the hyphae found in modern fungi.

He concluded that Prototaxites wasn't a plant at all, but rather a member of Team

And this was the same conclusion of another study done in 2007, that looked at the chemical

Now, how can chemistry tell you whether something's a fungus?

We talk about carbon a lot around here, because carbon is the stuff of life.

And different kinds of living things can be identified by how much carbon, and of what

The thing that researchers focus on here is the ratio of various isotopes of carbon, like

Plants have pretty consistent ratios of Carbon-12 to -13, because they all get their carbon

from the same place -- the CO2 in the air.

But things that eat instead of photosynthesize -- like animals and fungi -- pick up carbon

isotopes from their food, so their ratios can vary a lot.

And the 2007 study compared the isotopes in several fossils of Prototaxites from different

eras and found that those ratios changed radically over time, probably as its food sources changed.

This means Prototaxites was not a photosynthesizer, but an eater -- it got its food from other

Now, there's still a chance that this enormous not-plant-thing was something else, like a

Despite looking like weird plants, lichens are actually fungal hybrids that house their

So far, no one's come up with a good way to prove whether Prototaxites was a pure fungus