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

  • of Peru.

  • 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

  • fossilized.

  • 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 handor 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, reallydon'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

  • to the Pleistocene.

  • 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

  • placed in the same family.

  • 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

  • known as the Mega-Toothed sharks.

  • 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

  • record about 23 million years ago.

  • So, how and why did it get so huge?

  • 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.

  • And hunt it most certainly did.

  • 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 sharksuntil 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

  • its food source.

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

  • lived.

  • 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

  • shark.

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

  • hypothesis.

  • 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 mesothermicthey can keep their

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

  • even in colder waters.

  • 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

  • in the animal kingdom.

  • 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!

  • But unlike the suction-feeding sperm whales of our times, Livyatan had short, powerful

  • jaws.

  • And its teeth were big, strong, and meant for biting into flesh.

  • Also, at 17 meters long, Livyatan wasn't just snacking on squid.

  • It was eating other whales.

  • And it was only one of many species of carnivorous whales in the middle Miocene.

  • In the Late Miocene, another adversary shows up in the fossil record -- the earliest ancestor

  • of the Great White Shark, Carcharodon hubbelli.

  • This shark was a direct competitor with Megalodon, as proven by its tooth marks that have been

  • found in fossils of the same whale species that we knew Megalodon ate.

  • Namely, that little Piscobalaena.

  • Then, a few million years later, in the early Pliocene, the first fossils appear of the

  • modern great white, Carcharadon carcharias.

  • Now, in addition to having to compete with newer, more nimble sharks like these, some

  • of Megalodon's most important prey -- namely, whales -- were on the decline.

  • Toward the end of the Pliocene, the number of whales dramatically decreased from about

  • 60 whale species, to about 40.

  • Many of these species were filter feeders, and fed on krill and other organisms, which

  • in turn ate microscopic algae called diatoms.

  • And starting around 3 million years ago, the oceans began to experience a serious drop

  • in diatom diversity.

  • It's not 100% clear why this happened, but it might relate to changes in ocean circulation

  • that took place when North and South America finally came together, and water could no

  • longer circulate between the Pacific and the Atlantic.

  • Regardless of the reason, fewer diatoms meant fewer krill, which in turn meant fewer whales.

  • And with less food, Megalodon had to compete even harder with the smaller, faster great

  • white shark.

  • Being bigger is great, if it gives you the advantage of having access to a different

  • food group.

  • But when it no longer does, it just means you're bulkier and require more food to

  • survive.

  • Which is why, 2.6 million years ago, the very last of the Megalodon disappeared from the fossil

  • record.

  • And the absence of the Megalodon may have had a big impact on the world's oceans.

  • In the past couple million years, great white sharks and Orcas have taken over the roles

  • of apex predator, but these much smaller carnivores couldn't hunt the larger whales that Megalodon

  • was likely able to eat.

  • For instance, we know that modern Great Whites frequently eat dolphins half their size, so

  • it's possible that the 18-meter Megalodon was eating whales that were as big as 9 meters

  • -- much too big for other predators to handle.

  • And after Megalodon went extinct, the size of whales exploded.

  • During the Pleistocene, the waters grew colder, and the new and improved productivity at the

  • poles meant diatoms bounced back.

  • And this newly productive environment, along with the absence of large predators, meant

  • that whales were able to become twice as big as the biggest whales of the Pliocene.

  • This is why the blue whale, the largest animal our planet has ever seen, appeared in the

  • fossil record only recently - less than 2 million years ago.

  • Without 18 meter sharks swimming around, the oceans could finally host 25 meter whales.

  • So, Megalodon and its ancestors had a great run.

  • Over 30 million years, they became larger in order to eat larger marine mammals.

  • But when those mammals started to disappear, and when competition with Great White Sharks

  • and other predators became too fierce, Megalodon didn't make the evolutionary cut.

  • But it's worth noting that the biggest Great White Sharks of today are about a meter longer

  • than their ancestors were in the Miocene, and they grow a little faster when they're

  • young, too, just like Megalodon did.

  • It took nearly 30 million years for the mega-toothed sharks to reach the enormous size of Megalodon,

  • a slow transformation that took place as whales and other marine mammals slowly grew in size.

  • But whales today are already enormous, and face very few predators.

  • Which leaves the niche of super-shark wide open.

  • So it just might be that the Great White Shark could become the Megalodon of the future,

  • and that giant sharks might patrol our oceans once again.

  • Thanks for joining me today, and special thanks to our Eontologists, Jake Hart, Jon Ivy, John

  • Davison Ng and STEVE!

  • If you'd like to join them in supporting this channel, head over to patreon.com/eons

  • and make your pledge for some neat n nerdy benefits.

  • Now, what do you want to learn about?

  • Leave your girl a comment, and don't forget to go to youtube.com/eons and subscribe.

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

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Why Megalodon (Definitely) Went Extinct

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    joey joey に公開 2021 年 05 月 02 日
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