Eons

Kallie Moore: Around 250 million years ago, at the dawn of the Triassic Period, life on Earth was on its knees.

This was the direct aftermath of the most severe mass extinction event in history-- the Great Dying--triggered by colossal volcanic eruptions and runaway global warming.

The Great Dying lasted hundreds of thousands of years, leaving the supercontinent of Pangea scorched, desolate, and unrecognizable from the rich and dynamic world of the Permian Period that had preceded it.

More than 80% of the planet's species had been wiped out, and its shattered ecosystems-- both on land and in the water-- were now inhabited only by a skeleton crew-- an eclectic band of survivors from the Permian, the last remnants of the Paleozoic Era of ancient life.

And foremost among them was a tusked, beaked, and stocky herbivore, about the size of a pig at most, called Lystrosaurus.

It's not the most immediately impressive of ancient beasts, but in the Early Triassic, this little lumpy weirdo was the poster child for life on land, or what remained of it, at least.

Because, for a brief and, frankly, pretty bizarre moment in the history of life, after Earth had suffered its worst-ever mass extinction, Lystrosaurus ruled over the wreckage.

It was the big winner of the apocalypse.

At some Early Triassic fossil sites, Lystrosaurus is so abundant-- and other species so rare-- that it alone makes up more than 75% of the vertebrate fossils that researchers find, and as much as 95%, according to some estimates.

Lystrosaurus has earned the title of a "disaster taxon," a term that scientists give to groups that, at least temporarily, thrive in the aftermath of an ecological crisis.

So few other survivors emerged from the rubble of the Great Dying that disaster taxa like Lystrosaurus were suddenly freed from nearly all competition.

And even though much of the Early Triassic was still pretty hostile to most life, Lystrosaurus was lucky enough to have the right combination of traits to eke out a living, or at least a surviving.

Gabriel-Philip Santos: So for a couple million years or so following the end-Permian mass extinction, the surface of the Earth was a mostly pretty bleak place: hot, dry, almost totally treeless.

And in the water, a similar story was unfolding.

Marine life was devastated, with only pockets of surviving biodiversity clinging on here and there amongst the carnage.

The Triassic Period was off to a rough start, but it wouldn't stay that way for long.

Blake de Pastino: Eventually, those survivors from the Permian would find themselves replaced by a new wave of species, and whole new complex ecosystems unlike anything the world had ever seen before.

The Age of Reptiles was about to begin.

And while many features of the era of ancient life were lost forever, many now familiar features of the modern world emerged as the planet recovered, too.

The aftermath of the Great Dying was not just the graveyard of an old world but also the cradle of a new one.

[cricket chirps, creature grunts] Michelle Barboza-Ramirez: The five times when almost everything died-- or the Big Five mass extinctions, as we call them-- are considered to be the most destructive events in evolution.

But the fossil record also shows that mass extinctions aren't purely destructive forces.

By wiping the slate almost totally clean, mass extinctions open up new opportunities to surviving species that were beyond their reach before, suddenly catapulting obscure groups into the ecological spotlight.

And the pressure to survive those extreme events molds species in ways that leave a lasting evolutionary legacy.

Ecosystems don't just recover from mass extinctions, they often reform in ways that are radically different from anything that existed before.

And after the Great Dying, life on Earth was changed forever.

This almost complete reorganization left such a clear signal in the fossil record that it literally marks the end of the first era of complex life on Earth, the Paleozoic, which means the era of ancient life.

And the ecosystems that rose in life's middle era-- the Mesozoic--beginning with the Triassic Period were starkly different.

But that process took time, and for basically all of the Early Triassic, the ecological recovery on land was slow.

Having at least one really abundant species from the Early Triassic gives us a rare and valuable window into that world.

Because, while fossils of other species from this time are sparse, we have thousands of Lystrosaurus.

Its tusks and beak allowed it to access and feed on tough, dry-adapted vegetation, and it could burrow into the ground to find shelter from the elements or from the occasional surviving predator.

Plus, its widespread distribution across Pangea, from what's now Russia to Antarctica, suggests Lystrosaurus colonized the far corners of the supercontinent relatively quickly, thanks to its resilience and ability to tolerate a wide range of environmental conditions.

All of these traits, probably combined with a healthy dose of luck, allowed Lystrosaurus to survive and even flourish in the wake of the Great Dying, when almost nobody else could.

Caroline Abbott: One of the things that makes Lystrosaurus such a great animal to study is that we have it before the extinction in the latest Permian, during the extinction interval itself, and then into the earliest recovery from the extinction, the Triassic.

We have thousands of fossils of this animal, and Lystrosaurus survived the end-Permian mass extinction in enormous numbers.

Blake: And in all those bones, paleontologists have found clues that paint a picture of a world reeling from environmental shock-- one so hostile that even so-called disaster taxa struggled at times.

Caroline: Most of the fossils that we find from Lystrosaurus in the Triassic are quite tiny.

We get this huge overrepresentation of juvenile specimens.

The fossil record shows that Lystrosaurus from before the Great Dying lived up to around 14 years.

But after the event, patterns of bone growth show that most individuals were only living around 2 to 3 years.

In the harsh, unforgiving world of the Early Triassic, Lystrosaurus evolved to live fast and die young.

They likely reproduced earlier and more often because of their reduced life expectancy in these extreme conditions, accounting for the abundance of juveniles in the fossil record.

In fact, its flexibility in adapting its development and life cycle may have been one of the key reasons that Lystrosaurus was able to persevere as a disaster taxon.

But Lystrosaurus wasn't totally alone in the wreckage, and some of the other survivors were just as dangerous as the environment.

Kallie: At the top of the fragile food chain of the Karoo basin and elsewhere in the first million years or so of the Early Triassic was a leopard-sized therocephalian called Moschorhinus.

Before the extinction, Moschorhinus had been just one of many medium- and large-sized carnivores that stalked the landscape of Pangea, along with the huge gorgonopsians that were the apex predators of the Late Permian.

But while all those other big predators disappear from the fossil record around the mass extinction, Moschorhinus persists--the last large predator left standing.

Blake: Much like the Lystrosaurus it hunted, the fossils of Moschorhinus show that it was forever changed by the extinction event.

Remains of the predator from before and after show several intriguing differences.

After the Great Dying, individuals are smaller, and studies of their bone growth show that while their growth period was shortened, their rate of growth was actually faster.

This shrinkage seen in Moschorhinus, Lystrosaurus, and potentially other Early Triassic species has even been argued to partly explain a widespread but little-understood evolutionary phenomenon dubbed the Lilliput Effect.

This is the same animal, broadly speaking.

It's the same genus?

Yes, yeah.

Before and after?

Mm-hmm.

And that's significantly smaller than this.

Yes, yeah.

In paleontology, we find, oftentimes, after mass extinctions, small versions of the fossils that we were seeing before the extinction.

But why?

Like, what's the advantage of that?

Animals that are investing in a larger body plan are not going to be able to get the nutrients... Oh.

to persist.

If you change your growth trajectory such that you're a smaller animal that needs fewer resources, you're growing fast at a smaller size and reproducing more quickly.

That might be advantageous to living in a catastrophic environment.

Blake: Being smaller but developing faster might just be the evolutionary strategy that consistently works best in a post-apocalyptic world.

But how did the ancestors of us mammals--known as cynodonts-- survive?

Was it just luck?

Or did we have some evolutionary tricks up our sleeves, too?

In the Permian, the early cynodont species had never ever gotten big or committed to highly specialized niches, like so many other therapsids had during their heyday.

Instead, our cynodont ancestors had been smallish generalist carnivores that lived fast, energetic, and pretty scrappy lives, chasing small prey and dodging predators, kind of like the ferrets of their day.

You see, generalists tend to be much better at coping with environmental instability than specialists, who are highly adapted to and, therefore, very dependent on specific ecological conditions.

Kallie: And in the Early Triassic aftermath lived cynodont survivors, like Thrinaxodon, a weasel-sized ancient relative of ours that shared its environment with Moschorhinus and Lystrosaurus.

We've found many of its fossil burrows, sometimes with a Thrinaxodon still inside.

In fact, Thrinaxodon is the earliest known burrowing cynodont.

This makes it quite a trendsetter, seeing as around 50% of modern cynodonts--a.k.a.

mammals-- still burrow today.

And scientists have even proposed that burrowing may have emerged in Thrinaxodon and other cynodonts as a direct adaptive response to the hostile environment of the Great Dying and its aftermath.

It's a simple and common mammal behavior today that may have roots stretching back to an ancient apocalypse, and it's potentially one of the main reasons we're still around.

Michelle: This skeleton crew of animal life had it rough for pretty much the entire Early Triassic.

They were surviving, but to even begin to recover their former levels of diversity and abundance, they first needed their habitats to recover.

And the geological record suggests that may have taken a while.

See, researchers have identified a so-called "coal gap" that spans about 5 million years through the entire Early Triassic and into the Middle, where no rock layers from anywhere in the world contain deposits of coal.

Now, coal is formed by the compression of peat, which, in turn, is formed by accumulated plant material in wetland swamps and forests.

So a lack of coal deposits in the geologic record suggests an almost total loss of those plant ecosystems for millions of years, making it a pretty arid and barren phase of Earth's history.

Gabriel: So Pangea had lost its most diverse habitats-- forests and swamps-- and the marine realm had lost its equivalent, too--reefs.

See, while the fossil record on land shows a coal gap, the marine fossil record shows a reef gap that also lasts throughout the Early Triassic.

After being battered by rising temperatures, ocean acidification, and a loss of oxygen, 80% of marine species died out.

From reef builders to trilobites to sea scorpions, many ancient features of the world's oceans had vanished.

But there's evidence that in certain places and at certain times during the aftermath, a recovery was brewing below the waves.

For a long time, paleontologists thought that while some groups achieved unlikely success here and there in the Early Triassic, rich and complex ecosystems still weren't really a thing until 5 million to 10 million years later.

But in recent years, fossil discoveries in places like here in Paris Canyon, Idaho, have complicated that picture of Early Triassic Earth.

This site is way more exciting than it might seem.

Like, it's not that big-- it's only a couple hundred feet long-- and it's here on the side of the road, but it's full of this really amazing combination of animals that are really surprising.

And those animals are really important because they're right in, like, the very beginnings of the Triassic, really not that long after the Great Dying.

And they're helping us understand, like, how ecosystems were really more complex than we used to understand.

Gabriel: In 2017, paleontologists reported that they had unexpectedly stumbled on something amazing here buried in the rocks-- the fossil remains of a diverse marine ecosystem from just around 249 million years ago, less than three million years after the extinction event, when this area was a warm, shallow sea on the western edge of Pangea, close to the equator.

It featured fishes, cephalopods, crustaceans and other arthropods, sponges, bivalves, brachiopods, and more, all somehow thriving together when they should have been, well, dead.

This assemblage of species, known as the Paris biota, was a strange mix of ancient holdovers from the Permian and new species that show up for the first time.

Brandon Peecook: Oh, here we go.

Cool.

Right there.

That spiral.

Gabriel: That's cool.

What is that?

Yeah, that's an ammonoid.

So it's an animal called Tirolites.

It's super, super common.

We should find it a bunch in here.

This is one of the animals that actually lets us know how old the site is.

There's another one right there.

Oh, my g--Yeah, I told you.

They're everywhere.

They really are.

What other kind of creatures can we find in here?

Brandon: So things like squids and octopuses and cuttlefish today, they first show up in the Triassic, and some of the oldest fossils we have, they're called coleoids.

That whole group are, like, known from this site, like, right here.

But then there's also animals we find here that, like, shocked everybody when they were first found because some of them are animals that, like, disappeared hundreds of millions of years ago, or so we thought.

Uh-huh.

But here they are in the early Triassic, like, next to the lobsters.

Yeah, this is a little clam, so, like, a bivalve.

Oh!

Like the little shell?

Yeah.

It's pretty cute.

We've seen some brachiopods already, but that's, like, a nice, nice clam, so a different kind of little shelly guy.

Gabriel: This diverse community somehow stitched together a functioning complex ecosystem in the wake of the Great Dying, millions of years earlier than many scientists had assumed was possible.

And since the discovery of the Paris biota, similar evidence of rapidly recovering shallow marine ecosystems have turned up elsewhere, including in neighboring Nevada and even as far away as China, dating to as little as just 1 million years after the extinction event.

We understand and expect to see ecosystems not really recovering from the Great Dying until, you know, 7 million, 8 million, 9 million years after the event.

But this site's much, much closer to the event than that, and it's already, like, really complicated.

So there's a lot of surprises, right?

There's a lot of geographic variety probably in how life survived and recovered from the Great Dying, which is really, really, I think, exciting.

It means there's so much more to learn.

Gabriel: We still have a lot of open questions about how such rich ecosystems could recover so fast from the worst disaster of all time.

And in the years to come, we may find the answers to those questions.

But it's already clear that, at least in pockets of the marine realm, life was showing just how resilient it really was.

A new group of predatory reptiles was on the rise in the oceans of the Triassic: ichthyosaurs.

Ichthyosaurs, literally "fish-lizards," descended from land-dwelling reptiles that gave up on the terrestrial realm entirely and took to the water instead, sometime around the Great Dying or maybe even a little before.

Brandon: The first real ichthyosaur fossils we have are coming, like, right after the end-Permian mass extinction.

And so you have to realize that, like, the extinction is an opportunity, and ichthyosaurs are one of these groups that, like, really takes advantage and becomes full ocean reptiles.

Gabriel: With so little competition in the aftermath of the extinction, ichthyosaurs diversified rapidly, as parts of many other complex open-ocean food chains were recovering.

And while they started small, within just a few million years, some of them would become the largest animals the world had ever seen.

And by the Late Triassic, some even rivaled modern whales in size.

The sudden rise of ichthyosaurs in the wake of the Great Dying led to the first true ocean giants of Planet Earth, a feature of our oceans that we've had in some form or another ever since.

Michelle: Eventually, above the waves, life on land began to recover, too.

About 10 million years after the Great Dying, we see evidence that the landscape of Pangea wasn't so desolate anymore.

Dense forests regrew and spread across the world, providing habitats for new species.

This global reforestation left signals in the geologic record, like coal deposits showing up again as the vegetation that formed them returned, ending the coal gap.

And wood-boring beetles start showing up again in the fossil record, too, reemerging after a gap of their own at this time as their forest habitats recovered.

Complex terrestrial ecosystems were reforming, but this new era of life on land would be different from anything that had come before.

As the Triassic recovery played out, synapsids, including our cynodont ancestors, found themselves facing intense competition, and it came from their ancient cousins from the other side of the amniote family tree.

The Triassic marked the start of the Age of Reptiles, and their dominance of terrestrial ecosystems would last for a very long time.

Blake: If Lystrosaurus was so what, resilient and adaptive as a generalist and it survived the thing that destroyed almost all of life on Earth... Caroline: Yeah.

then what happened to them?

How did their story end?

So Lystrosaurus didn't live that far after the Early Triassic.

It was really abundant in the recovery interval from the extinction.

But then as ecosystems return to normal and we start seeing a higher diversity of species going into the later parts of the Triassic, Lystrosaurus disappears pretty quickly.

You would think that if it's so good at surviving the worst thing that has ever happened to life on earth, that it would be fine competing with a few reptiles and Archosaurs and other dicynodonts that are persisting.

But, no.

That's really remarkable.

Yeah.

That's a heck of an evolutionary strategy.

Like, when things go wrong, that's when they're really in their prime.

And then when things settle down again, the conditions become more difficult for them.

Yes.

Yeah.

It's like they're adapted to chaos.

Blake: Just as ichthyosaurs were the rising stars of the Triassic oceans, another group of reptiles was vying for ecological prominence on land--the archosaurs.

They started out as a pretty obscure reptile lineage that survived through the Great Dying.

And as the planet recovered over the course of the Triassic Period, they underwent an explosive evolutionary radiation.

Archosaurs began filling an array of ecological niches that had been left mostly empty by the mass extinction, outcompeting and replacing disaster taxa like Lystrosaurus.

Take the pseudosuchians, for example, a branch of ancient archosaurs related to modern crocs.

They diversified into everything from giant apex predators to armored herbivores.

One group of archosaurs, known as the pterosaurs, even took to the skies, becoming the first known vertebrates in history to master powered flight.

And somewhere in this explosion of reptile diversity was a lineage of upright, slender archosaurs that was about to give rise to one of the most spectacular animal dynasties the world ever saw: the dinosaurs.

Michelle: The earliest true dinosaurs arose about 233 million years ago.

And they were only side characters compared to other branches of the archosaur family tree.

But during the Late Triassic, that suddenly changed.

Much of that archosaur competition on land fell away, and dinosaurs were catapulted to the ecological forefront.

And just in time, too, because Pangea was starting to break up, and its fragments would carry the dinosaurs over the globe over the course of the Mesozoic Era.

Their reign over Planet Earth had begun, but that's a story for another time.

Blake: The Paleozoic Era of ancient life was well and truly over, and life's middle era, the Mesozoic, was in full swing.

But the story of the synapsids that had lived and died on Pangea continued into the Age of Reptiles.

Because scurrying here and there, rustling through the undergrowth of dense Late Triassic forests, a pretty familiar group had finally emerged: mammals.

They had evolved from a lineage of cynodonts that had been both lucky and scrappy enough to survive not just the Great Dying but also the challenging and increasingly competitive world of the Triassic.

And by the Triassic's end, cynodonts were the only synapsids left.

Today, we mammals are the last remaining branch of what used to be a huge, diverse, and once-globally successful synapsid family tree, with roots stretching back to the era of ancient life.

While synapsids had seemed unstoppable in the Permian, in this world dominated by dinosaurs, the earliest mammals became mostly small and nocturnal to survive-- quite literally cast into the shadows.

Child: Dimetrodon.

[Duh-metch-ruh-dahn] Dimetrodon.

Dimetrodon.

Dimetrodon... The Permian, in my eyes, is more important than the dinosaur age because this is where our roots come from.

You know, your cousin is buried right here 290 million years ago.

Christopher Flis: This is where humanity comes from in a sense, and it's always surprising us.

You know, every time we think we know something new about the Permian, it changes our minds.

The Permian is a really important time period because it is so early in the evolution of life on land.

And we're really getting a snapshot of how vertebrae animals were exploring how to live in this new place.

This is sort of where the ancestors of the mammals show up--our ancestors.

These dinosaurs that aren't dinosaurs, really.

Rrr!

When you get, like, a pack of dinosaur toys, and it's in there for some reason.

You know, you look at a Dimetrodon, you're like, "Oh, that's a dinosaur."

But they're not dinosaurs.

They're actually a close relative of mammals.

Dimetrodon and the Edaphosaurus, they are still very relevant.

The synapsid body plan, the idea that something could look and act more or less like the mammals would later on simply isn't likely just like any form of life.

And so the fact that not only did that happen but we have such a good record of it here, that success story is just really cool.

Without this Great Dying, we wouldn't have had Age of Dinosaurs as we saw it.

So, you know, for a paleontology person, that's kind of cool.

But I'm a human first, so I'm team synapsid.

So the fact that they were knocked out, some of the traits that were required to survive this event led to us mammals-- assuming you're a mammal watching this-- rising up again and, in the Cenozoic, taking it from there on.

And so that's why it's such a big deal that we were knocked back to appreciate where we are today.

Gabriel: With something as terrifying as the Great Dying, you know, when almost all life was wiped out, it's pretty inspiring in a way to be able to see life just carry on and be resilient.

Studying the Permian is really important because we can really understand so much of our story from that.

This is when so many things go extinct.

This is when so many things recover.

It's that really incredible story of life on earth, and being able to see it through the lens of the Permian and how life and death on Pangea was happening, it's...it's just really, really cool!

Blake: Today, we're finally bringing the epic saga of the Permian Period back into the light with us.

Gabriel: Because while the world of the Permian is long gone, it is no longer forgotten.

Michelle: And while it still doesn't always get as much attention as it deserves, considering it was both the best and the absolute worst of evolutionary times-- its story is one that we're slowly rediscovering.

Kallie: 252 million years after the Permian ended, at least some descendants of the species that lived and died on Pangea are coming to know what it means to be a living legacy of one of the most pivotal and radical chapters of deep time.

"Eons" "Life and Death on Pangea" is available on Amazon Prime video