The Mystery of Earth's Disappearing Giants | IN OUR NATURE

I want you to imagine for a moment that you've

been instantly transported through time. 50,000 years in the deep past,

what you see would shock you. In North America, you gaze upon

short-faced bears, larger than a grizzly. Mastodons. Dire wolves. Saber-toothed cats.

In Australia, you'd be eye to eye with a gargantuan wombat

and see monitor lizards half as long as a bus. In South America, sloths as tall as elephants,

automobile-sized armadillos. Rodents the size of small bears.

In Europe, towering arc cattle, wooly mammoths, even lions, hippopotamuses, and hyenas.

And in Asia, an elephant that stood a full head above today's largest African bulls.

During Earth's glacier covered Pleistocene Epoch, every continent was home to mammalian giants,

the megafauna, species that dwarf their relatives alive today. But during the last 50,000 years,

these giant mammals, plant and meat eaters alike, have gone extinct on every continent except one.

Today, Africa is home to nearly all giant land animals left on Earth. The mystery is why?

These giant animals are so awesome. I wish that they were still here. It's not fair.

Why did they have to disappear? I always heard That it was our

fault. Humans and our spears hunted mammoths and all that stuff to death.

Well, there's definitely a correlation between when humans arrive in a place and when its

megafauna disappear. The earliest anatomically modern homo sapiens, they show up around 300,000

years ago in Africa. It wasn't until around 50 to 70,000 years ago though, that we first left

Africa in big numbers. First to Asia and Europe, then to Australia, and finally the Americas. So

compared to human origins, human expansion across the globe it just happened so fast.

According to archeological evidence, less than a thousand years after the first humans that

crossed the Bering land bride, they were already at the tip of South America. So outside of Africa,

at least, the megafauna must've been like, "Wow, there's suddenly humans here." Just like that. But

at the same time, humans hunting every large animal on five continents to just nothing,

it seems too simple. Yeah. There's theories to

explain the extinction of megafauna and they've been debated really fiercely for decades.

I think what we really need though, is a time capsule.

Lucky for you, Trace, we actually have one and it's in the last place you would expect.

Right here in Los Angeles. Plot twist! I thought it was just influencers.

I've been working with Ranch La Brea fossil since like 2010. I guess you could say that I got stuck.

That's Mairin. She's a scientist here at the La Brea Tar Pits, which includes a museum

and a research site that's active in lots of different ways. This is the best place

on earth for understanding the ice age extinction. This thing

is absolutely incredible. We are looking down into a giant pit. It's bubbling.

There are odors. It's exciting. There's pollen. I don't know what's happening.

There are also sounds as the gases bubble up to the surface, make this [inaudible 00:03:46] sound.

Yeah. Yeah.

It's clearly still a really dynamic place. How did all of this come to be?

These tar pits were here since before the city of Los Angeles was established and they've

actually been here over the last, at least, 55,000 years.

Back then, the tar pits, or more accurately, asphalt seeps oozing up and out of the ground,

were concealed under water or leaves and anything unlucky enough to go

in was also unlikely to get out. So wait, it's like quicksand? The

tar just gets them, sucks them in, and preserves their remains like a giant vat of sticky pickles?

Yeah, pretty much. The green flag over there marks a

saber-toothed cat shoulder blade. What?

Yeah. And the blue flag marks a giant ground sloth pelvis or hip bone.

Can you imagine giant ground sloths being here in Los Angeles today? That in itself

is mind blowing to me. [crosstalk 00:04:45].

And then saber cats. I'm sorry. It's like you have a whole party here of all these different animal.

Paleontologists love it when fossils are stacked like a sandwich. They're easier to understand and

place in time. But because of this seeping, moving asphalt and the fact that California is still a

really tectonically active place, over thousands of years the fossils in this soup pot get all

jumbled and mingle-mangled. This sticky trap is still sticking today. Just like it was when all

these other cool animals were walking around. I love me a good fossil sandwich with a side of

oozy tar soup. Yum. Even 2000 years in the future, I think they would

find a really interesting record of life today. Wow. Maybe plastic or trash even.

To remove the fossils from the sticky resting place, staff and volunteers

have to use airplane degreaser. And afterwards, they're sorted and placed in these collections

where researchers can look at them firsthand. That seems like a mammoth effort.

That was a megafauna mega funny folks. Yeah. This is like putting together a puzzle.

One that is a million pieces and it's all stuck, covered in like GAC and sticky stuff.

GAC. GAC.

GAC. On the left we have our giant grand sloths and

on the right here, we have other large herbivores. For example, right now we're passing by bison.

We are talking shelf after shelf of ancient ice age bison, ground slots, mastodons, tapirs,

hundreds of thousands of fossils grouped by species and anatomical element.

Whole shelf Of baculum. That's penis bone.

So these aren't all from one individual. These represent dozens if not hundreds of different

individuals. Exactly.

That's this bone here. [inaudible 00:06:36] right over here.

That's huge. And this is from a camel? From a camel who lived in North America.

So that's the big question, they were here and then they weren't. What happened?

What happened? Maybe the secret is here

in this very drawer. Maybe this bone right here. This bone right here.

Could hold the secret of why we don't have camels anymore.

Narrator, unfortunately, it didn't hold the secret.

I want to get back to the big, important question here. Why don't we today have

camels and all these other cool animals anymore? How do all these bones pulled from this tar pit

tell us why megafauna disappeared? Yeah. Let's back up and take a look

at the competing ideas as to why these absolute units went extinct.

Scientists studying the decline of megafauna at the end of the Pleistocene first focused their

attention on North America. Partly because of large troves of fossils like those at La Brea but

partly because that's just where the scientists were from. The sudden arrival of humans in North

America and this sudden disappearance of large mammals seemed too closely timed to be a mere

coincidence. Likewise, megafauna extinctions in Australia and on Pacific islands were also

timed closely with early human settlement. Scientists, like Paul Martin, concluded that

humans armed with a new stone weapon technology known as Clovis points swept through the Americas

decimating the large mammal population. It became known as the Blitzkrieg or Overkill hypothesis.

The problem was we now know there were humans in most parts of North America for thousands of years

before Clovis point technology showed up and we just haven't found any of the large

collections of remains that suggest early Americans were hunting on this scale. So

Overkill has become more of a no overkill idea. There was a second idea which also blames our

species. A slower, drawn out extinction only partially due to hunting combined with early

humans changing the environment through setting fires, deforestation, habitat loss,

and negative effects from the critters we brought with us, like cats and rats and dogs and things.

This may explain the extinctions of giant island dwelling birds, like dodos and moas,

but again, there's little evidence that the first humans in the Americas changed the environment to

this degree. The fossils at La Brea are helping paint a different picture of the extinction of

Pleistocene giants. So are they only

pulling out giant extinct species? No, that's the cool thing. They're

not. They've recovered coyotes, bobcats, foxes, skunks, and badgers. Species we still have today.

So here we have our typical coyote skull, for example. It's the same species of coyote that

we have today, Canis latrans, but found in deposits that could be 55,000 years old.

Okay. So wait, let's put the giants aside for a minute and instead of looking at why megafauna

disappeared, I think it's interesting to think about what survived, all the medium things. What

happened to let these regular fauna persist? Think about it, compared to a giant cave bear

or American lion, if you're a raccoon or a skunk, you eat less, probably reproduce

faster and likely have more available habitat. A badger takes up way less space than a mammoth.

It seems like the fossils should be able to tell us was this some big extinction tidal

wave that affected all of the species or were the big stuff already just about to kick the

bucket and something pushed them over the edge? So the clues that can lead us to those answers,

aren't the fossils we've been talking about. In fact, they're not animal fossils at all.

Well, here we are. This is the Wait.

Paleobotany collection. These four cabinets?

Well, there's some more but Okay.

this is part of it. Here's some of the wood that's preserved.

Oh my gosh. Yeah. It's a beautiful

brown texture because of the asphalt that stains it. This is from juniper and that's probably

the most common wood fossil that we have here. They find plants at La Brea too. And what's so

cool about all the plants they find here, they have modern relatives, meaning they still exist.

Look at these. So these are oak leaves and they're just perfectly preserved, right?

They look exactly just like the leaf litter. Okay, you can hold this one.

Oh my gosh. They look just like something you would find on the sidewalk on a fall day.

Exactly. You'll notice these fossils are quite a bit smaller. They're all in their own vials.

They're tiny. I'm seeing this one. It's in a pill capsule.

Yeah, exactly. It's so tiny. Every time

I see stuff stored in pill capsules I have the like the innate urge to just swallow it.

These are from Pit 91. They're from the top of Pit 91. So this is probably

right around the time of the extinction. So this is a pretty significant specimen.

It is. It actually is. Yeah. Wow. I could be ingesting the

You could. mysteries of the universe.

These plant microfossils, from bits of leaves to seeds and pollen grains,

stuff so small you need a microscope to see them. These micro plant parts

paint an even more detailed picture of what was happening than even those large

mammal fossils do. But finding these itsy bitsy, teeny weeny bits of leafy greeny, isn't easy.

It's like Looking for a literal pine needle in a tar pit.

Yeah, but what's so cool is that those really small bits can be big clues.

How did these fossil plants and their remnants fit into this bigger story?

In order to understand the ecosystem at all, you have to start with the primary producers.

How does changing climate affect animals? It affects them through the plants that they

eat, that they live in, their habitats. Really understanding the plants and what happens

because of the climate to the plants is key to understanding the response to the animals later.

So let's say you find pollen from ragweed, junipers pines,

daisies, and sunflowers that would indicate this region had a dry arid climate, not unlike today.

Okay, but how do you go from pollen to the extinction of gigantic mammals?

Maybe they sneezed to death. No Trace, but you can compare these microscopic

plant fingerprints over time to see how the plant species change. And that's a really good indicator

of the overall climate. What scientists at La Brea have noticed is that the plant species did

in fact start to change about this same time these megafauna disappeared from the tar pits,

right around 12,000 years ago. Which was also just a few thousand years after

humans show up in North America. Now that is quite a coinkydink.

I know, but it's more than that. The plants tell us at the end of the Pleistocene, Earth's climate

was changing drastically likely affecting what giant animals could eat, where they could live,

and how they could move from one place to another. Okay. So that makes sense. The effects of a

changing climate is likely a big reason why Earth's megafauna went extinct. So

does that mean that it wasn't humans fault? Not necessarily. Humans still probably had

an impact here. For example, we've got evidence at the tar pits of more fires, but why? Because

it's getting hotter and drier or because people were setting them or something else?

Obviously alien space lasers and very large magnifying glasses. I

know it's not either of those things. This is what I mean when I say that

extinction is a messy business. Right? Nature is pretty resilient, short of like an asteroid

or something. Extinctions are usually just not caused by one thing. I think with these complex

systems you have to change a few things in huge ways or a lot of things in pretty big ways between

people and plants and animals and the climate. Our current best understanding of what happened in

North America is also kind of messy. It probably wasn't just one thing but many disruptions

of a complex web of interactions. Decreasing habitats, human impacts, global climate change,

these trends are really familiar to us today. This past that we've been talking about was really

not so long ago in the scale of life on Earth, at least. Understanding how things played out then

can inform our future and there's. That combination of factors that wiped out so many

prehistoric megafauna species; climate change and humans killing them and changing their habitat.

These are the same challenges facing Africa's giants today. Only all those factors are taking

place at scales and speeds that just dwarf the changes of the past. Our impacts reach every

corner of the planet today and it's playing out faster than at any time since our species evolved.

We need to understand that while our impact may be larger than other species on Earth,

we aren't the only species on Earth. Right? To find a place that's still so full of

it's rich megafauna, is so rare nowadays. It's very much something that hooks you in place in

the world. To see the sense of scale, just how large the savanna is and all the megafauna and

these incredible vistas. I don't know. There's something very humbling about that. Putting

it in a grander sense of scale, this is where humanity developed. This is the cradle of mankind.

Think about that. The earliest human ancestors descended from their Australopithecine

predecessors right here in the rift valley of east Africa, nearly 3 million years ago.

That is an incredible sense of connection. This is kind of where we evolved. Isn't that cool?

And this gets at one possible reason why African megafauna made it. For more

than a hundred thousand years, Africa's giant species were co-evolving with us,

with homo sapiens. And they lived alongside our specie's ancestors before that.

Early humans in Africa, they certainly hunted these giants and modified the habitat in big

ways. But living alongside humans for so long coevolving that could have given Africa's

megafauna a resilience that the other giants just didn't have. Outside of Africa, human's

sudden global expansion combined with rapid climate change at the end of the Pleistocene

might've meant that evolution couldn't keep up. There's a lesson in the past hidden in those

tar pits. If the environment changes too fast, things disappear on massive scales

And the story locked in those plant fossils that ancient climate change happened over

tens of thousands of years, the climate changes we're seeing today, they're happening on the scale

of decades and they're even more severe. That really puts into perspective how

quickly our climate is changing today. Megafauna aside, places like the tar pits

are offering more supportive evidence of how our climate slowly shifted in the past in comparison

to this rapid shift, we're seeing today. Big things disappeared more than once on

five different continents. We have to understand that that can happen again.

There's really nowhere else on earth that you find the scale of animals in number, but also,

like I said, in size. It would be cool if there was elephants walking around everywhere, but

we've changed the planet in ways that just doesn't seem to be able to support what we

see here. I think that's just what makes it even more special. It's something to

remind us of how much of the world used to be. To be able to study these ecosystems with the

megafauna intact gives us a much better understanding of how environments change

and we could lose all of this. Think for a second about how we're trying to

protect the surviving giants today. We're drawing lines on maps, creating these protected places,

but that's not enough to protect these species and these ecosystems. Because the challenges that

we're facing today, they don't pay attention to those borders. And think about the risks of losing

these ancient migrations, these deep animal cultures, these long lasting relationships,

highly developed skills and senses. The ways of surviving in this place and all of these places,

it'll take tens of millions of years to restore the biodiversity that has disappeared from Earth,

just since the dawn of our species. These are things that are

built into them with millions of years of evolution

to do the things that they do in this place. Changing that in a few human years

is asking a lot, maybe too much of these species. So you may not be able to go to Africa yourself

or fix climate change on your own, or save every species from extinction with your own hands,

but there has never been a better time for individuals to make a positive impact.

So true. Volunteers help protect that Mission blue butterfly. And scientists

climb trees to understand how to save forests. Passionate people listen to birds singing during

a pandemic. All of these people do their part and we don't know how big our impact might be.

But we have to try because the only way to find the answers is to keep looking for them.

When I was at La Brea, I saw just how much there is to still learn about our place in all of this.

It kind of blows my mind. A hundred years ago, the people who were initially excavating these pits

could probably not have any idea that you'd be able to

look at this on literally such a granular scale. Yeah. I'm the only other person that's ever looked

at this. So you're the second person in the world. What?

In the history, in the whole record of time to see these specimens.

That's pretty amazing. I can discover a new species today. Here on camera.

You probably already did and you just didn't know it.