[Wind blowing] ♪ Michelle Barboza-Ramirez: Here in the West Texas desert, a fossilized wonder of the ancient world juts out from the dry and rugged landscape.

These towering mountains, known as the Guadalupe Mountains, were formed through biology becoming geology.

Once upon a time, they were alive.

See, the Guadalupe Mountains are built from the ruins of a vast tropical barrier reef.

♪ Blake de Pastino: In the middle of the Permian Period, around 270 million years ago, this reef flourished along the edges of a shallow inland sea that filled a basin close to the equator on the supercontinent Pangea.

The reef is hundreds of kilometers long and curves into what's now New Mexico, and it once teemed with countless species, big and small, that thrived in the habitat it provided.

♪ Gabriel-Philip Santos: That massive fossilized ecosystem is a spectacular relic of the Permian, the final chapter in the Paleozoic, and it's been on quite a journey since then.

[Water trickling] ♪ Michelle: When a climate crisis dried up the inland sea, the reef became buried in sediment for over 200 million years, locked in time as the world changed around it.

Pangea broke up, the dinosaurs rose and fell, and whole eras of deep time came and went, with this Permian reef staying hidden underground through it all, until, starting around 25 million years ago, tectonic forces from deep within the Earth lifted it up, allowing erosion to reveal the towering, fossil-strewn cliffs we see today.

It's a grand, one-of-a-kind window into a fascinating time in the story of life on Earth, but a time that would end in disaster.

Because this reef, along with a great deal of Middle Permian life, was doomed.

♪ Kallie Moore: The same crisis that dried up the inland sea and buried the reef was only part of a much wider climate catastrophe that devastated life on Earth as the Middle Permian drew to a close.

And it hit our proto-mammal relatives on land pretty hard, too.

But their story, and the story of the reef, shows that while the Permian period is long gone, its legacy can still be found in our modern world, if you know where to look.

♪ ♪ Blake: The Middle Permian stretched from about 273 to 260 million years ago, and it's formally known as the Guadalupian Epoch, named for the mountain range containing the reef.

And during this epoch, life on Earth was a blend of both strange and familiar.

The vast tropical barrier reefs of the Middle Permian, for example, are a feature of the modern world, too.

But the reef in the Guadalupe Mountains wasn't built primarily by corals, like most of today's reefs are.

Instead, it was the multi-generational project of an array of other ancient reef builders, including mound-building algae and microbes, as well as sponges and other invertebrates.

As they died, the remains became cemented together, building up a framework for each new generation to grow on and expand further.

♪ [Wind blowing] So, we're in the Guadalupe Mountains, which are mountains, in terms of, they are tall pieces of land, but when people think of mountains, or at least when I talk to my students, a lot of the times, folks don't know what that means.

In this case, this mountain is a reef.

Look at this, look at this.

There is a sea urchin that is just perfectly fossilized here.

You can see each individual spine still attached to the urchin.

And as you give yourself some time to get used to what the fossils look like in an area, the longer you're there, the more they're gonna start popping out before your eyes.

So, let's move over just a smidge.

Every single little line you're seeing here, every line here, every line here, all of this beautiful stuff is shells.

OK, where are you at, my friend?

I know I saw... Ah!

Oh, my god, OK, here it is, here it is.

Check this out.

So, this little, like, line of Cheerios are called crinoids, and crinoids are related to sea lilies, which are still around today.

All of these little white lines that you're seeing are the outlines of the fossil shells.

Just shell, shell, fossil, fossil, fossil.

We're in the Middle Permian Sea right now, traveling in time, with the fossils below me.

♪ This reef was just one of many complex and multilayered ecosystems, similar in structure to the ones we know today that had formed by the Middle Permian, both in the water and on land.

But, in many cases, the species that filled those ecosystems were unlike anything alive today.

Throughout the marine realm of the Permian, trilobites scurried across the sea floor, ammonoids bobbed through the open waters, and bizarre sea monsters lurked.

♪ Gabriel: I love the ocean.

I love ocean life.

It's always been something that I've been interested in.

Ever since I was a little kid, I would do marine science programs.

I went to aquariums.

I loved whales and all those really cool marine creatures.

And that really led into how I got started as a paleontologist.

There's just so many cool stories when it comes to the ocean and things that we can learn about when it comes to our story, or just the story of life itself.

Take Helicoprion, for example, a huge, ancient, shark-like predator that swam through the waters of the Guadalupian Epoch.

Some estimates have placed it at over 8 meters long, making it possibly the largest-known animal of its day, though, like all shark relatives, Helicoprion had a skeleton made up almost entirely of cartilage, which often doesn't fossilize well, leaving us with a lot of open questions about it.

But it's the one piece of literal hard evidence that we have found of them that has ended up leaving paleontologists especially puzzled.

Giant whorls of teeth, unlike anything seen in the animal kingdom today.

Brandon Peecook: Helicoprion is one of these animals that just has an anatomy that really challenges us.

Obviously, this animal existed.

Obviously, it existed well.

It was evolved to live in its habitat.

It lived for quite a long time.

There's many species of it.

And now it's our job to try to figure out, like, what this thing is, what it's doing.

It's really crazy.

Gabriel: Where exactly these whorls fit and what Helicoprion was using them for were debated by paleontologists for decades.

Hypotheses range from the whorls coiling upwards from Helicoprion's snout to hanging downwards from the lower jaw, to maybe even sprouting from Helicoprion's fins as defensive structures.

It wasn't until scientists studied an especially well-preserved tooth whorl with bits of fossilized tissue still attached, that in 2013, they were actually able to reconstruct it with confidence.

This is one of the specimens that's been CT scanned and shown us the actual structure of the jaws.

So, we know now that this great, big, weird circle of teeth is, like, set right in the middle and only on the lower jaw.

Another thing that's kind of interesting is that we see these teeth are quite sharp, and throughout the animal's life, they're never worn down.

So that helps us understand it's probably eating, like, really soft things, like the relatives of squids and things like that.

That's Amazing.

So, definitely, no spinning buzz saw.

Definitely no, like, rum-rum-rum-rum-rum spinning.

But, like, unless you count, like, the whole animal putting in new teeth throughout its life, the whirl does--you know, it doesn't rotate, like, with a click like this, but it does kind of always grow out.

And so, there is a bit of a spin over the course of a lifetime.

All right.

So Fred Flintstone wouldn't have used it as, like, a tree cutter.

It would be very ineffective.

Ah, OK.

[Laughs] So, species across the tree of life were evolving all sorts of innovative adaptations as they became specialized for particular ecological niches within their environment, often ones that no animal had filled before.

It's a recurring theme of the Permian Period.

And on land, our proto-mammal relatives were no exception.

They, too, were specializing in weird and wonderful ways.

[Film reel rolling] ♪ Blake: Terrestrial life in the Middle Permian had just undergone an important evolutionary turnover.

In the Early Permian period, the more reptile-looking pelycosaurs had their golden age.

They were an early wave of synapsids, the side of the amniote family tree more closely related to mammals than to reptiles.

And they had pioneered many of the first ecological niches on land for big vertebrates, including everything from herbivores to apex predators.

But as the Early Permian drew to a close, the pelycosaurs mysteriously declined, and by the Middle Permian, a more advanced wave of synapsids had risen to ecological prominence in their place-- the therapsids.

Therapsids were often faster and more agile, with a greater range of motion in parts of the spine and legs that held their bodies higher off the ground, though some still had sprawling limbs like the pelycosaurs.

Plus, they had more robust skulls, more complex types of teeth, keener senses, and a faster growth rate.

These adaptations allowed them to not just pick up where the earlier pelycosaurs had left off ecologically, but to evolve in ways that had never been seen before.

So, these animals are definitely more mammal-like than, like, the pelycosaurs that came before them.

They're really helping us understand bits and pieces of how the mammal body plan kind of came to be, but they're certainly not, like, on the way to "mammalness," if that makes sense.

Yeah, they're just, like, experiments along the way.

Yeah, and there's so many of them, and there's, you know, big ones and small ones, herbivores and carnivores.

Blake: The most prominent early therapsids that roamed the landscape of the Middle Permian belonged to a group called the dinocephalians, who experienced a dramatic rise and fall across the Guadalupian Epoch.

And their name, which literally means "the terrible heads," refers to the group's big, thick skulls that sometimes featured elaborate bony ornamentation.

It's thought that many dinocephalians used these skulls for headbutting each other in competition for territory, mates, and social status, like many modern mammals do today.

This makes the dinocephalians perhaps the earliest terrestrial animals to show specialized traits for highly-complex social behavior.

Complex traits of behaviors that we now think of as typical of modern mammals, from our physiology to our sociality, were emerging for the first time here and there across the synapsid family tree.

The origin of true mammals was still a long way off, though, and the dinocephalians themselves wouldn't be directly involved.

They went totally extinct at the end of the Middle Permian, dying out around the same time as the reef.

But during the 13-million-year- long Guadalupian Epoch, the dinocephalians flourished.

They radiated into a diverse array of herbivorous, omnivorous, and carnivorous species across the food chain, with some being among the biggest land animals of not just the Permian Period, but the entire Paleozoic Era.

Kallie: These giants included Moschops, for example, a dinocephalian herbivore that grew up to around 2 meters long.

Moschops had a thick skull, specialized for head-butting rivals, and a bulky, lumpy body with a huge gut, for fermenting plant matter.

And its front legs sprawled at its sides, while its hind legs were more upright beneath its body, which is pretty weird.

Moschops had a strange mosaic of traits that are individually found across the tree of life but have never come together in a single animal in quite the same way, before or since.

Moschops is really interesting, because it really helps demonstrate how you can have traits that you didn't expect would be in the same organism, absolutely in the same organism, and living really successfully in its environment.

And odd combinations of features turn out to be pretty characteristic of life in the Permian Period.

Another striking dinocephalian from the Guadalupian Epoch is named Estemmenosuchus or "crowned crocodile" for its elaborate bony skull projections.

As with many other dinocephalians, Estemmenosuchus probably used these antler-like structures for its own particular style of head-butting combat, likely locking heads with rivals and pushing against them.

And these projections may have also been a more general form of sexual display, signaling health and fitness to potential mates.

So, if you think about, like, horns or antlers on big, herd-living, plant-eating animals, that's really familiar.

Horned dinosaurs, elk, whatever.

And so, it's interesting and fun, I think, to see it way back there in the Middle Permian.

Like, one of the first times life is playing with this sort of suite of characteristics that kind of go together really nicely.

And higher up on the food chain were dinocephalian carnivores, including some of the biggest and most dangerous terrestrial apex predators of the entire Permian Period.

Take Anteosaurus, for example.

Anteosaurus reached around 5 meters long and 1.5 meters high, with a thick, bumpy, and crested skull, powerful jaw muscles, big, sharp canines, and bone-crushing teeth.

And it was like nothing the world had ever seen before.

Older terrestrial apex predators had been slower and ambushed their prey, like Dimetrodon from the Early Permian.

But recent reconstructions of Anteosaurus have suggested that it may have been a much faster and more agile kind of predator.

Think of, like, a lion today.

This is a very capable cat that can have fast bursts of speed, can chase you down, is really agile.

And Anteosaurus has a lot, kind of, more in common with something like a lion than it does with Dimetrodon, even though they're both in the Permian.

This is an animal that's, like, standing more upright.

We know it's capable of moving pretty quickly.

It has some sensory adaptations that give us an idea that it was, like, a pretty agile animal.

When we see these, like, different features altogether, you know, here in the Middle Permian, Anteosaurus is just a very competent apex predator.

And Anteosaurus was probably among the very first land animals to ever live like this-- one of evolution's first attempts at a terrestrial carnivore that was both big and swift, a combination that's proved successful ever since.

Blake: While the Guadalupian Epoch was the heyday of the dinocephalians, they weren't the only land animals, or even the only therapsids, that roamed Pangea at this time.

The supercontinent was huge, and its habitats were varied, meaning that all sorts of ecological niches existed and were filled by other strange Permian species, like another group of therapsids called the therocephalians, who also emerged in the Guadalupian.

Some of the earliest therocephalians were medium-sized predators, including Lycosuchus, whose name means "wolf crocodile."

This up-to-three-meter-long carnivore had a relatively short and broad snout, featuring two sets of large, sharp canines.

How exactly they used these double fangs when hunting their prey is hard to know for sure.

We have no modern equivalents to compare them to.

But it's thought that Lycosuchus hunted smaller prey than the giant apex predator Anteosaurus, probably including juvenile dinocephalians.

And so, you are seeing in the Middle Permian kind of the development of these, like, tiered structures to ecosystems.

It's not as simple as plant eater, meat eater.

There's gradations within the trophic hierarchy for some of these carnivores.

And so, something like an Anteosaurus is going to maybe be your apex predator.

Animals like Lycosuchus, very successful in that ecosystem, a different group of animals altogether, but still, again, a very competent predator.

Blake: And from the sauropsid, or reptile, side of the amniote family tree came the pareiasaurs-- bulky herbivores similar to their dinocephalian counterparts like Moschops, though lower to the ground and with bony armor.

Pareisaurs represent an early experiment in reptile gigantism, long before the first dinosaurs emerged-- a completely independent and much more ancient branch of big, lumbering reptiles.

One of the earliest and most common of these bulky ancient pareiasaur reptiles was Bradysaurus, which weighed about as much as a large modern cow.

The success of Bradysaurus in this large-bodied reptilian herbivore niche paved the way for around 20 other pareiasaur species to evolve over the course of the Permian.

It was Earth's first wave of giant reptiles, but certainly not its last.

It seems that wherever you look in the fossil record of the Middle Permian, you find examples of species breaking new evolutionary ground, developing traits, behaviors, and lifestyles that had never been tried before, but have re-emerged many times since.

So, life on Earth in the Guadalupian Epoch was flourishing, from gigantic reef complexes that stretched for hundreds of kilometers through the water to the diverse and often huge synapsids and reptiles on land.

But it wasn't to last.

So, right at that Middle-Late Permian boundary, we have this extinction event, and really maybe even a mass extinction event.

♪ Much of this biodiversity died off at the transition from the Middle Permian to the Late Permian, victims of an extinction event that hit around 260 million years ago.

This mass extinction at the end of the Guadalupian is often forgotten about in natural history, though some researchers argue that it, and potentially others too, should actually be added to the Big Five mass extinctions, making it part of a Big Six, or Seven, or Eight.

And it doesn't get the credit it deserves, probably because a mere 8 million years or so afterwards-- a blink of an eye in geologic time-- another, even more severe one followed-- the Great Dying at the very end of the Permian Period, the worst mass extinction ever.

We'll get to that story later, but the size and scale of the Great Dying tends to overshadow the End-Guadalupian extinction that preceded it.

In fact, it was only in 1994 that researchers first proposed that the End-Guadalupian event was its own separate crisis, making it one of the most newly-recognized mass extinctions in paleontology.

The once-diverse dinocephalian therapsids disappear entirely from the fossil record around this time.

Some of the biggest and most successful land animals the world had ever seen so far-- gone in an evolutionary instant.

At the genus level, the diversity of vertebrates may have dropped as much as 80%, and nearly half of this diversity decline comes from the total extinction of the dinocephalians.

But while not every group disappeared entirely like the dinocephalians, it seems that all groups of land animals lost at least some lineages.

The therocephalians, as a group, survived through the crisis, for example, but their early members, like the lycosuchid wolf-crocodiles, did not.

Pareiasaurs survived as a group too, although they lost some members, like Bradysaurus and its relatives.

So, what could have caused this catastrophe at the end of the Guadalupian?

Well, it's still the subject of a lot of debate, and few things about it are known with certainty.

But, tantalizingly, it coincides with a period of volcanic activity in what's now China that may have rapidly altered the global climate.

Evidence of these huge ancient eruptions can still be found in southwestern China today.

It takes the form of a geological feature called the Emeishan Traps-- layers of hardened volcanic rock stretching over 250,000 square kilometers and averaging 700 meters thick.

It was probably caused by a superheated plume from within the Earth's mantle, melting and bursting through the crust.

And while the debate is still ongoing, some researchers have argued that this dramatic geological event is the most likely culprit behind the mass extinction.

These eruptions around 260 million years ago would have released enormous quantities of greenhouse gases into the atmosphere over the 2 million years or so that they lasted, potentially warming the planet by around 4 degrees Celsius.

Many ecosystems may have become unstable under such significant and relatively rapid warming, which would explain the loss of biodiversity seen in the fossil record around the same time.

And it may explain why the biggest animals-- the dinocephalians, along with Bradysaurus and its relatives-- disappeared so completely.

Larger animals need more resources and generally struggle to cope with dramatic shifts in their habitat.

In the marine realm, these eruptions would have also had disastrous consequences, increasing the water's temperature and acidity while reducing oxygen levels.

And this might explain the extinction of a range of species in the marine fossil record at the end of the Guadalupian, marking a major shift in ocean life.

And like all mass extinction events, we know about it best from the ocean, oceanic fossils.

So, the kinds of animals that are making reefs literally out of the seawater with their bodies.

We can track changes in diversity really well with animals like that.

And as we go from the Middle Permian into the Late Permian, we see one of those big turnovers, and we see a big loss of species.

Gabriel: And the reef in the Guadalupe Mountains had an especially dramatic downfall.

Right around the marine and terrestrial mass extinctions and the eruptions of the Emeishan Traps some 260 million years ago, this reef was frozen in time.

A global drop in sea levels, possibly driven by the sudden climate disruption caused by the eruptions, eventually cut the shallow tropical sea basin off from the ocean.

The seawater evaporated, leaving the reef high and dry until it was gradually buried by minerals, mud, and sediment.

♪ Blake: We still have a lot of questions left to answer about the mass extinction that ended the Guadalupian Epoch and the Middle Permian as a whole.

Since it's a relatively newly recognized mass extinction, it's also among the least understood.

But the fact that it coincided with the Emeishan eruptions is hard to ignore, because it's exactly the kind of trigger that we know is powerful enough to destabilize the biosphere.

This seems to be a recurring pattern in paleontology that's only become clear over the last few decades.

The majority of mass extinction events in the fossil record match up with periods of intense volcanic activity.

And it's not hard to imagine how this could be more than just coincidence but causation.

The biosphere is pretty resilient.

Given enough time, life can adapt to all sorts of global changes and conditions.

But adaptation takes time, and if change comes too quickly, mass extinction follows.

And, other than the occasional unlucky asteroid impact, massive volcanic eruptions are among the few events known to be capable of rapidly triggering intense and global environmental changes.

By destabilizing the global climate through their mass release of greenhouse gases, eruptions of this size also end up destabilizing life.

Today, another force has emerged that's capable of triggering sudden global change in a disturbingly similar way--us.

And if our actions trigger changes too intense and too quick for a species to adapt to, we may have to add a new mass extinction to the list.

♪ Michelle: The fossilized reef here in the Guadalupe Mountains and the volcanic rock layers of the Emeishan Traps can be thought of as a pair of contrasting geological windows into the past, allowing us to glimpse the ups and downs of life in the Middle Permian.

They're two ancient relics that have survived over 260 million years, each telling fragments of the same story to those who know how to read the rocks.

On the one hand, the reef shows how Middle Permian life thrived and created magnificent complex ecosystems, rivalling those of today.

And on the other side of the world, the flood basalts of the Emeishan Traps may show precisely how and why many of those ecosystems collapsed.

But this crisis at the transition from the Middle to Late Permian was only a warm-up act for something much bigger to come.

Because, as we'll see, life will find its feet again in the Late Permian, adapting, innovating, and recovering from the extinction event, only to be hit by a catastrophe of even greater proportions that will end the Permian Period and the era of ancient life itself.

Complex life would soon have its closest-ever call with total extinction.

And just like the Middle Permian extinction, it would begin with a rumbling from deep within the Earth.

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