Name: 南極が緑だった頃 (When Antarctica Was Green)
Uploaded: 2021-01-14T11:18:54.000Z
Duration: 12 min 14 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：

It's the world's most remote and isolated continent.

It's home to glaciers, mountains, plants, and penguins, but today, Antarctica is also

In modern Antarctica, there aren't any trees, or any native terrestrial mammals, reptiles,

Thanks to plate tectonics, Antarctica has been connected to lots of other continents

As a matter of fact, before the start of the Eocene Epoch about 56 million years ago--Antarctica

was still joined to both Australia and South America.

And the fossil record tells us that, in the early Eocene, Antarctica was a warm, forested

place, very different from the continent we know today.

Palm trees thrived there, as did flowering plants, dung beetles, and even a number of

And because of the way it was situated, Antarctica probably served as an important migration

path for the ancestors of some of the southern hemisphere's most charismatic mammals, like

Eventually, of course, the lush environment of Eocene Antarctica transitioned into the

cold, glacier-covered landmass that it is today, isolated from the rest of the world

by the most powerful ocean currents on the planet.

But it turns out that a lot of what we recognize about the southern hemisphere -- including

those famously unique animals of Australia -- can be traced back to that time when Antarctica

If you could travel back in time and visit Antarctica in the Eocene Epoch, the first

thing you'd notice would probably be the greenery.

Off the coast of Wilkes Land, in eastern Antarctica, scientists have discovered sporomorphs--fossilized

pollen and spores -- from ancient palm trees and ferns.

And they've also found pollen from other plants that often live in tropical environments

The traces of these warm-weather plants can tell us a lot about what Antarctica was like

Since these palms and other trees can't tolerate the cold very well, paleontologists

think that, in the early Eocene, the coast of Wilkes Land experienced very mild winters,

By one estimate, the mean annual temperature of that part of Antarctica was around 16 degrees

Celsius, with an average winter temperature around 11 degrees Celsius.

So, how could ancient Antarctica have been so warm?

Well, for one thing, the Eocene wasn't the first time that Antarctica's climate was

Scientists have found sporomorphs and other fossils from warm-weather plants in Antarctica

that date way back to the Devonian Period, more than 358 million years ago.

And in the early Jurassic Period, about 190 million years ago, Antarctica was a temperate

home for dinosaurs like the long-necked Glacialisaurus and Cryolophosaurus, a crested carnivore.

In those days, Antarctica was just one small chunk of the supercontinent Gondawana, and

was located a bit farther north than it is now.

But by about 100 million years ago, most of the landmass that would become Antarctica

By the early Eocene, the western part of Antarctica had just split from the tip of South America,

but the eastern part was still mostly linked to Australia.

And right around this time, the world was going through a dramatic heat spike.

This event is known as the Paleocene-Eocene Thermal Maximum, and we did a whole episode

about it, because the theories about what caused it -- and what made it stop -- are

really complex, fascinating, and little scary

During this period, the global average temperature increased by 5 to 8 degrees Celsius in 220,000

And as the world's climate changed, so did its flora and fauna.

Tropical trees like palms, as well as ferns and tree-ferns, were able to spread onto every

And mind you, Antarctica is a really big place; like...the entire country of Australia can

So given its size, it was able to support many different ecosystems in the Eocene.

Farther inland, and at higher elevations, sporomorphs and leaf impressions have been

found from plants that are normally found in temperate rainforests, like southern beech

even experienced monsoons, getting more than 60% of their annual rainfall in the summer.

And of course, plants didn't have the whole continent to themselves.

On Seymour Island, off the Antarctic Peninsula, paleontologists have recovered brood balls

Those are balls of dung that female beetles lay their eggs in.

So if these beetles were rolling dung balls around, where did that poop come from?

Well, some of it came from ancient marsupials!

Fragmentary remains and isolated teeth tell us that a number of these little mammals lived

Judging by their teeth, it seems that some of them belonged to the same order of marsupials

as the modern colocolo opossum, a small and adorable insect-eater that's native to South

Another Antarctic marsupial was Antarctodolops.

First described in 1984, this opossum-like critter was the first terrestrial mammal ever

discovered in the continent's fossil record.

Its ancestors most likely came over from South America.

Other residents of Eocene Antarctica probably came from South America as well.

For example, a single contentious toe bone suggests that xenarthrans--the group of mammals

that includes modern-day sloths--might have lived in Antarctica.

Xenarthrans originally evolved in South America, as did the forerunners of a hoofed herbivore

that's been found in western Antarctic, called Notiolofos,.

The teeth of this creature tell us that it was a browser, stripping twigs off if tree

branches and maybe eating the occasional sapling.

Not many specimens have been found, but we do know there were at least two species of

Judging by the sizes of their teeth, the bigger of these ungulates weighed up to 230 kilograms

while its smaller cousin was about one-fourth that size.

And the fact that these two species had such different sizes means that they might have

both been specialists, eating different types of plants to avoid direct competition with

Another big hoofed mammal known from Eocene deposits in West Antarctica is Antarctodon,

Scientists think it was a kind of astrapothere, an unusual group of extinct and mostly South

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南極が緑だった頃 (When Antarctica Was Green)

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