Name: Why Megalodon (Definitely) Went Extinct
Uploaded: 2021-05-02T00:54:34.000Z
Duration: 11 min 13 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：

About 8 million years ago, a little baleen whale was swimming in the warm coastal waters

様態の副詞

It was only about 3 or 4 meters long, about the size of a Beluga whale, and while it filtered

mouthfuls of plankton-rich water, it was unaware that just below it swam a predator.

Like the great white sharks of our times, this predator likely hunted whales from below

or behind, in case its prey was capable of echolocation.

It turns out that this little whale, known as Piscobalaena, didn't have that ability,

but for the hunter, the element of surprise was enough.

It swam up for the attack, and that was that for Piscobalaena.

We know who the predator was, because it left a tooth in the whale's body, which eventually

It usually goes by its species name, Megalodon, and it was the largest shark that ever lived.

At up to 18 meters, it was almost three-quarters the size of a modern Blue whale.

Its teeth were as big as your hand – or bigger.

And its jaws were wide enough to swallow you whole.

Megalodon lived all over the world, from the Netherlands to New Zealand.

And for more 10 million years, it was at the top of its game as the oceans' apex predator

… until, 2.6 million years ago, when it went extinct.

Yes, really – don't let Hollywood convince you otherwise. I know you're smarter than that.

Megalodon disappeared entirely from the fossil record, just as the Pliocene epoch gave way

And there's also proof of its extinction in the composition of marine life that we

find today -- especially in the kinds and sizes of whales that swim in our modern oceans.

So, what happened to the largest shark in history?

Well, it turns out that while Megalodon may have been the biggest shark that ever swam,

it would eventually be defeated by the greatest.

Megalodon was the biggest, scariest shark in a family of big, scary sharks.

It belongs to the diverse order of sharks known as Lamniformes, which today includes

sand tigers, goblins, threshers, and the Great White.

And when Megalodon was first described in 1835, scientists thought that its big, serrated,

blade-like teeth looked so much like those of the great white that Megalodon was originally

But today, based on features around the base of its massive teeth, most experts think it

was probably in a separate family whose members are all now extinct, called Otodontidae, also

Now, one of the oldest and smallest of the group of Megatooths that gave rise to Megalodon

was a shark known as Otodus obliquus, which lived in the Early Eocene, nearly 20 million

years before Megalodon appeared on the scene.

And some scientists think Megalodon belonged to this same genus, Otodus, while others assign

it to another genus of extinct sharks, called Carcharocles.

Either way, Megalodon was the largest of all the Megatooths, first showing up in the fossil

Well, Megalodon's massive size was linked to the size of its prey.

And both were shaped by forces much bigger than themselves.

These external forces began at the end of the Mesozoic, when plate tectonics caused

the uplift of mountains in North America and Asia.

The weathering of these growing mountain ranges pumped massive amounts of nutrient-rich sediment

into the oceans, increasing the productivity of ecosystems near the shore.

And as the algae and plants grew, so did the preferred food group: marine mammals.

Marine mammals like whales, dolphins, and seals all have pretty high fat contents, making

them a nutritious, high-calorie snack for any predator that can catch them.

And as the marine mammals grew over time, so did the sharks.

Over the course of about 20 million years, marine mammals and the line of Megatooth sharks

that led to Megalodon both doubled in size!

And Megalodon in particular started to grow fast.

Fossils of newborn megalodon, found in places like Panama, show that they were about 2 to

3 meters long, half the size of a modern great white shark, and about one and a half times

as large as their ancestor Otodus obliquus!

And these massive baby sharks grew like weeds.

We know this because shark vertebrae show rings of their growth, just like tree rings.

And these rings show that Megalodon babies grew almost twice as quickly as Otodus obliquus,

reaching their maximum length at around 25 years old.

So, getting bigger over time, and then getting bigger faster, probably helped Megalodon keep

up in the ongoing size race with the marine mammals they hunted.

Its teeth have been found stuck in the ribs of many unidentified whale species, as well

as the tiny Piscobalaena, and even in a pinniped about the size of a sea lion.

So, size was a very useful adaptation for the giant sharks – until it wasn't.

Because 2.6 million years ago, Megalodon disappeared.

And there are a couple of potential reasons for this.

For one thing, 2.6 million years ago marked the beginning of the Pleistocene, when cooler

temperatures and long periods of glaciation began to set in -– also known as the Ice Ages.

This change in temperature could have affected Megalodon directly, or it could have impacted

That's because the change in climate led to a restructuring of how and where whales

As the climate shifted, more productive environments with more food began to take shape closer

to the poles, so whales started to spend a lot more time there and became more migratory.

So maybe the problem for Megalodon was that its prey started moving to where the water

was colder -- too cold, perhaps, for Megalodon to follow.

For a long time, scientists thought this might have been what did in the world's biggest

But in 2016, a group of researchers led by Dr. Catalina Pimiento decided to test that

Specifically, they tested the assumption that Megalodon couldn't live in cold water.

Pimiento and her team used a climate forecasting model to recreate ocean temperatures during

the Pliocene and Miocene, and compared those temperatures to where Megalodon had lived.

They found that while the shark preferred water from about 12 to 27 degrees Celsius,

its fossils were still found in places where the water was as cold as 1 degree!

So Megalodon probably was okay with colder water.

Which makes sense, because many large sharks today are mesothermic – they can keep their

bodies a little warmer than the surrounding water temperature, which helps them stay active

So, if changes to the whales' movement and habitats wasn't the problem then what was?

Well, the disappearance of Megalodon seems to coincide with two big, important changes

The first was the appearance of new predators that Megalodon had to compete with.

For example, starting around the middle of the Miocene, we find the giant sperm whale

with the epic name of Livyatan melvilli, named for none other than the author of Moby Dick!

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Why Megalodon (Definitely) Went Extinct

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