This program was funded by: The Theodore F. and Claire M. Hubbard Family Foundation encouraging public understanding of natural history, past and present.

(percussive music) (zebra running) NARRATOR: Africa has long been renowned as a land of origins, vast grasslands, (elephant trumpeting) and exotic wildlife.

(rhino snorting) NARRATOR: But on America's great plains, paleo sleuths have found fossils that challenge popular understanding of origins during the age of mammals.

(digging in dirt) ROSS SECORD: This is volcanic ash.

This layer right here, this is where they go extinct.

SHANE TUCKER: Really, really exciting when you get the whole skeleton like this.

This is a very rare occurrence.

DR. MIKE VOORHIES: It's a tooth of a four tusk elephant, it's the first kind of elephants that came to America 14 million years ago.

MARK NORELL: There's really five or six great places in the world to find fossils, and Nebraska's really key among that, because it really preserves rocks which are anywhere between about 35 to about four million years old.

(blowing) And the fossils are incredibly plentiful.

DR. VOORHIES: That's a little section of a rhino skull.

NARRATOR: Much of what the world knows about the age of mammals is found beneath this vast landscape in America's heartland.

Enter a prehistoric world when mammals ruled supreme, and embark on a fossil safari that reveals how changing climate transformed North America from hot, wet forests to frozen grasslands.

Exploring prehistoric worlds has been the life's work of Nebraska paleontologist Mike Voorhies.

DR. VOORHIES: I think it's kind of a shock to think that not that long ago, geologically speaking, we had a variety of wildlife that would rival the present day tropics.

I wouldn't have believed it myself if I didn't actually see remains of these creatures buried in the rocks here.

Somehow we have to explain how they got here, and eventually, why they disappeared.

NARRATOR: Sunrise.

Earth's clock begins as our natural world unfolds, day by day.

But what's known about the timeline of nature's past is often a mystery.

DR. VOORHIES: I think a lot of people have a hard time coming to grips with the idea of millions of years.

We're all accustomed to the idea that the Earth has changed, but most people, if you tell them that the hills and valleys didn't used to be here, that's a real shock.

But actually, to a geologist, the hills and the valleys are very recent.

They have been carved by erosion in fairly recent times.

NARRATOR: The geology that formed the Great Plains is far older.

Prior to the age of mammals, a shallow inland sea covered the region from the Gulf of Mexico to the Arctic.

The sea began draining when uplift forced the Rocky Mountains to rise 65 million years ago.

Then, sediments began spreading eastward to gradually fill that basin layer upon layer to form the plains.

Over time, some of those layers began covering remains of animals with sand, gravel, and silt, eventually preserving them as fossils.

DR. VOORHIES: And so we have a pile of sediment from about 40 million years to the present that has preserved the very detailed record of the evolution of wildlife buried in our rocks.

It's not as though these animals didn't live elsewhere, it's just that most places, they're not preserved.

But Nebraska has been almost like a page in a book has been printed every year for the past 40 million years, and we have the privilege of going out and reading that book.

NARRATOR: Americans have been trying to understand those layers of time since the colonial era.

DR. VOORHIES: When fossil remains were first found in the early days of America, the first teeth of mastodons that were found were thought to be giant human teeth.

And a number of preachers believed that these giant teeth were confirmation of the verse in the Book of Genesis, "there were giants in the Earth in those days."

And it wasn't until about the year 1800 that the first complete skeleton of a mastodon was found, and finally it was realized that these were not remains of human giants.

No one on Earth had any concept of evolution as we understand it today.

NARRATOR: The origin of fossils generated a spirited debate, pitting natural philosophers of old world Europe against upstart Americans, including President Thomas Jefferson.

DR. VOORHIES: Not very many people realize that Thomas Jefferson was a major scholar, very interested in fossil elephants.

French intellectuals in Thomas Jefferson's time pretty much made fun of America.

They even made fun of our wildlife.

Jefferson went out of his way to find examples of American animals that were way bigger than anything in Europe.

NARRATOR: Jefferson's fascination with natural history was a major factor in his decision to launch Lewis and Clark's Corps of Discovery.

Their mission to seek a trade route to the Pacific included secret instructions to chart plant and animal life, rare or extinct.

DR. VOORHIES: Jefferson considered fossil remains of very large animals as being part of God's plan for the Earth.

And for many years, Jefferson refused to believe that animals could become extinct, because to him, this would imply that creation was somehow imperfect.

And that was one of the reasons he really wanted Lewis and Clark to find live mastodons and mammoths, was because extinction, to Jefferson's mind, implied an imperfect world.

NARRATOR: The explorers never observed mammoths.

But guided by Native Americans, Lewis and Clark found 200 new plant and animal species, and recorded several fossil specimens in their journals.

Lewis and Clark were among the first paleo sleuths.

Since then, many others would follow, and even today, they all share a native link to the land.

(doors closing) On the plains of Oklahoma, paleontologist Kent Smith is carrying on a tradition of his ancestors with a new generation called Native Explorers.

KENT SMITH: We're gonna walk over where the cream and tan exposures are above the red bed, that'll be of the age that we're looking for to find some mammal fossils.

(digging in dirt) I'm a member of the Comanche Nation, and most of our students are either Cherokee, Choctaw, or Chickasaw.

Native Americans, like scientists, are curious.

They're always investigating, pursuing the animals and plants and knowledge, the interconnection between them.

(footsteps) MASHELI BILLY: I've been able to feel a connection with the Earth and with the spiritual elements that bring us people together.

SMITH: In the Great Plains, there are multiple very rich fossil sites that Native Americans have been very well aware of.

NARRATOR: Today, the Native Explorers are prospecting a former ash quarry where pumice was once mined for household cleansers.

ALVIE LAVERTY: One day I was up here walking around, kind of seeing what I could find, and I came across this pretty good sized chunk of bone.

It's right here.

SMITH: That's beautiful.

We have kind of a modern horse that's about 500,000, 600,000 years old.

BILLY: It's really incredible that, you know, that we can come in here and find bits and pieces of something so old.

(scratching in dirt) NARRATOR: Horse fossils played a major role in early paleontology.

(train horn) NARRATOR: It began when the first railroads opened a gateway to the American West in the 1860's.

DR. VOORHIES: Among the earliest scientific explorers was O. C. Marsh of Yale University.

Got on the Union Pacific, and one of the places he stopped was Antelope Station, Nebraska, and they had recently dug up a well near the railroad.

The diggers brought him a bunch of fossils.

A bunch of teeth that they had dug up out of this well, and Marsh immediately recognized these things as the remains of ancient horses.

NARRATOR: Marsh realized he had chanced upon a vast region rich in fossils.

But to find more, he would have to tap the wisdom of locals, and no one knew the land better than Native Americans.

SMITH: When the early scientists came over to study and try to find fossils, they went to Native Americans to find out where these fossils were located.

NARRATOR: Led by Native American scouts, Marsh's first expedition to Nebraska's Niobrara River Valley unearthed a crucial discovery.

There, he unearthed the oldest known single toed horse limb.

It was the missing link in a chain of fossil horses.

In his journal, Marsh writes.

READING MARSH'S WORDS: "I have since unearthed, with my own hands, not less than 30 distinct species of the horse tribe, and it is now, I think, generally admitted that America is, after all, the original home of the horse."

NARRATOR: When Charles Darwin published The Origin of Species in 1859, there was very little fossil evidence that evolution occurred.

DR. VOORHIES: What Marsh's horse story did, for the very first time, it actually showed how a particular type of animal had changed through time.

Marsh had actually proven Darwin's case for him.

NARRATOR: Marsh's sequence of horse fossils was so convincing that Charles Darwin cited it in a letter as the best evidence supporting his theory of evolution.

By the 1870's, the Great Plains became a hotbed for fossil collecting.

An array of gritty Nebraska sites, like Devil's Gulch, Agate Springs, and Valley of the Snake River lured the top names in paleontology.

Now, paleo sleuths can descend into the cellars of time in an expansive terrain so remote and desolate that it evokes an alien world, far beyond the pastoral plains of Nebraska.

This series of sandstone, silt, and clay canyons is Toadstool Park, known as the White River Badlands.

ROSS SECORD: This is really an amazing place that we're in right here.

These are badlands, we're in a desert here, and what makes this so wonderful to somebody who's a paleontologist is the preservation of fossils is also wonderful here.

And we have a better record through this interval of time than just about any other interval of time in North America.

This was an amazing place in the past too, and extremely different than it is now, because it would've been forested, it would've been much warmer, it had mild winters, it had a lot more rainfall than it does now, it would've had rivers running through here, these rocks were all deposited by rivers, and then there's continual volcanic ash falling down, which is what helps preserve the fossils so well.

NARRATOR: This angular, hardscrabble landscape has been shaped by erosion from rain and wind.

SECORD: This is world class fossil collecting here.

NARRATOR: A wide variety of wildlife flourished here eons ago.

One of the most plentiful was a small browsing animal.

SECORD: So here we have a partial oreodont skull, and this was a really common animal at this time.

These were small little herbivorous mammals that ate plants, they had a head and teeth that are similar to sheep today, but the body was quite different, they just had short little legs, so in that sense, they were more pig-like.

So sort of across between a pig and a sheep.

NARRATOR: This open landscape was once teeming with a wide variety of wildlife, and many were far smaller than the animals of today.

SECORD: This is a tooth from a small rhinoceros that lived at this time, and these are some of the earliest rhinos, the size of a large dog.

They were fast runners, and they're in the same group of mammals that the horses are.

(footsteps) NARRATOR: In the shallow canyon below this rim are traces of abundant herds of animals.

SECORD: This is a sandstone bed here, and it's related to a river channel.

This is pretty cool.

This is a fairly rare thing to find.

Here we have an ancient trackway of a small rhinoceros that lived at this time.

You can see the prints, here's a print here, another print up here.

On some of these you can actually make out the individual toes.

Most of the animals that we see here were eating leaves at this time, which is one of the reasons why we think that there wasn't much in the way of grass around.

NARRATOR: This badland terrace was once dominated by exotic beasts of titanic proportions called brontotheres.

SECORD: So we're seeing brontothere bones coming out of the ground in a number of places here.

These things are related to horses and rhinoceroses.

This species had a pair of horns that came off of its nose, which were probably covered in sort of a rawhide.

You can think of this as a giant rhinoceros that would've been eight feet tall at the shoulder.

So these were massive animals.

They were huge.

Most of the animals that were around at this time were a lot smaller.

There were horses, which were fairly small, there were camels that were a little bit taller and very slender, so this was by far the largest thing that was around at this time.

Here we're seeing some of the largest of the brontotheres and the last of the brontotheres.

NARRATOR: Along these ridges is a clue to critical habitat change.

(digging in volcanic ash) SECORD: This is volcanic ash.

(digging in volcanic ash) And you can see this white bed right here stands out really well among the other beds, but the important thing about it is it contains minerals that are dateable, and recent age dates on this place it at 34 million years ago.

NARRATOR: The ash layer signals important changes in climate and extinctions.

SECORD: We're able to correlate these rocks globally to events that are happening all around the world.

And in particular what we see at 34 million years ago is that in Antarctica, there's large ice sheets starting to form.

Ocean circulation has changed, so what we're seeing because of that is the global climate is changing at this time.

NARRATOR: This layer of 34 million year old ash marks a significant climate shift from the wet, dense tropical forests of the Eocene below to drier, more open bushlands and forests of the Oligocene above.

SECORD: This layer right here that you can trace the titanotheres or the brontotheres up to, and this is where they go extinct.

You find them below this boundary, you don't find them above this boundary.

NARRATOR: For the next 20 million years, plants and animals that adapt to the changing habitat continue thriving across the American landscape.

For eons, a series of ancient rivers has been reshaping the contour of northwest Nebraska.

Some rivers have slowly deposited layer upon layer of sediments, while more recent waterways, like the Niobrara River, have sliced through those layers of time.

DR. VOORHIES: A channel cut by a river at some point fills up with sand and gravel.

When the main river current goes someplace else, you can have several feet of sediment accumulating.

But there was one layer in the Rosebud.

NARRATOR: For paleontologists Mike Voorhies and Greg Brown, the Niobrara Valley has been critical for collecting fossils.

DR. VOORHIES: A very good place for a burial to occur is along the channel of a river.

And in order to preserve a critter as a fossil, it has to be buried fairly quickly.

99.99999 percent of all the critters that live and die, they don't end up as fossils, they just end up...

They're being recycled back into nature.

(flowing water) NARRATOR; For more than a century, paleontologists have been drawn to the rich fossil beds of the Niobrara River Valley.

But no one explored the Niobrara Valley in more detail than a self-taught local youth named Morris Skinner.

He began collecting in 1926.

MORRIS SKINNER: As a child, I always liked natural history.

And I got acquainted with a kid with the same interest as mine, Jim Quinn, and we spent part of the summer of 1926 and we went out in the canyons and by god, there was one side of a bank just covered with bones, and we started digging bones.

(Model T driving past) We just went where we wanted to go with an old Model T. (Model T driving past) And we'd look for these old ancient river beds.

But we didn't have any trouble finding fossils.

NARRATOR: Soon, they amassed an impressive collection, and began sending crates of fossils to museums.

One source was a private collector named Charles Frick at the American Museum of Natural History in New York City.

MARK NORELL: Western Nebraska is a very important place for this collection.

You know, we have floors and floors and floors of fossils that came from this area, and largely through the efforts of Skinner and other Frick collectors.

(door opening) The American Museum of Natural History has the largest collection of fossil vertebrates of any museum in the world.

(cart rolling past) And that makes up well over two million specimens.

(drawers opening) NARRATOR: Of those, a surprising number were unearthed by Morris Skinner.

BOB EVANDER: Morris found a lot of different kinds of animals.

There were elephants, there were lots of horses, he knew where they came from, he knew where they fit in time.

The guy managed to collect 46,000 specimens in his life.

That's a lot of specimens to collect.

That's a big number.

NARRATOR:Skinner's fossil discoveries influenced a generation of new paleontologists, including Mike Voorhies.

DR. VOORHIES: Hi, Morris.

MORRIS SKINNER: Mike.

DR. VOORHIES: Pretty damn good, how's yourself?

SKINNER: We knew of this since about 1926, and we came down this old trail here and there's bones laying all over the surface.

DR. VOORHIES: This site now has produced 144 species of extinct vertebrae.

SKINNER: Unless you have compelling evidence, I'd rather throw them away then send them in without a record.

You gotta prove when that animal lived.

That's the point that I try to make to all these fellas, is if they collect the specimen, if they don't collect the collateral data with it, they've just got a pretty rock.

DR. VOORHIES: This river has only been here for 20,000 years, so it has absolutely nothing to do with the fossil bed that got deposited here, oh, maybe 100 feet above our heads.

NARRATOR: Voorhies and Brown are now revisiting Skinner's site.

14 million years ago, this ridge was an ancient riverbed.

DR. VOORHIES: Now there's my very favorite river in the world.

GREG BROWN: Beautiful river.

I wonder how many future fossils are laying in the bed of this river.

DR. VOORHIES: Yeah, yeah.

Just imagine.

DR. VOORHIES: This is the bone hunter's river.

This is the place you come to understand the evolution of North American animals in the last part of the age of mammals.

(shaking screen) This particular site that Morris Skinner discovered is basically a jungle river.

Just crammed with remains of all kinds of critters from the size of elephants down to the size of tiny little mice and shrews.

DR. VOORHIES: Ooh.

BROWN: There you go.

DR. VOORHIES: There you go.

It's the common genus of frog.

(emptying screen) Man, it's good to see bone here again after all those years.

Wow.

The sweet sound of bone.

This is not a place where you find whole skeletons, you find lots of single bones and jaws and teeth.

BROWN: Well, I would think it looks like a humerus, upper arm bone, to maybe a gomphothere, it looks like, a four-tusked elephant.

DR. VOORHIES: Yeah, sort of the, it's the thing that would be just above the elbow, and it's so big, the only two possible chances would be either a rhino or an elephant, four-tusked elephant.

One of the reasons this is an important site is that this is when the elephants discovered America.

Elephants actually came to America 14 million years ago, and the fossils that we're finding here are examples of those very first ones that came over from Asia.

NARRATOR: Their arrival was made possible when low sea levels brought a submerged land bridge to the surface, linking together the continents of Asia and North America.

DR. VOORHIES: There hadn't been anything like them, ever, in America before.

These very primitive early elephants are actually a lot different than modern-day elephants.

They had very short, powerful legs, they had a real long head with a long lower jaw, they could tilt their head down and put their lips in the water and drink just like a cow or a horse, they didn't have to have a trunk to suck up the water the way modern-day elephants do.

(scraping dirt) It is a tooth, or at least it's part of a tooth.

Definitely one of the four-tusked elephants.

With a tooth like this, he really couldn't grind his food, but he could crush the juice out of fruit or leaves.

That's basically the way they ate.

They ate food that was soft enough that it did not require lots of processing.

They were very much at home in forests, they would've starved to death in a prairie, like we have here today.

NARRATOR: And there are precise clues that indicate that the climate 14 million years ago differs greatly from those of modern times.

DR. VOORHIES: It's some fossil wood.

That's very useful, because you can learn quite a bit about what the climate was like by looking at the rings.

(counting rings) I count about 35 years of growth here.

This was a time when we had heavy, dense forests, things with cyprus trees, palm trees.

You can see that pretty much all the tree rings are the same width.

It tells you that the climate rainfall didn't change much from one year to the other.

So basically, there's like the Garden of Eden for these elephants.

NARRATOR: The warm, stable conditions found here would endure for millions of years across North America.

But slowly, drying conditions would allow grasslands to expand, restricting forests to the borders of waterways.

Not all fossil sites are found in such pristine surroundings.

Some are detected in the most unexpected and disturbed settings.

(van driving past) Between March and November, Shane Tucker crisscrosses Nebraska's highways.

(van driving past) Tucker is a paleo sleuth of a different kind, searching for fossils in the man-made world.

Much of his work involves checking sediments in crevices as a University of Nebraska State Museum paleontologist.

(truck driving past) SHANE TUCKER: I follow road construction projects throughout the state throughout the year in order to save fossils from destruction by heavy machinery.

NARRATOR: What makes Tucker's quest unique, (truck driving past) is his unlikely group of helpers.

(truck door closing) CONTRACTOR: We're sitting right up over here.

Okay, he's gonna grade for a four-lane, but we're gonna pave for a two-lane.

NARRATOR: As Nebraska's highway paleontologist, Tucker encourages Department of Roads crews to look out for fossil remains.

TUCKER: I brought some bones out to kind of show you guys.

This is a complete lower jaw from a bison.

You're kind of looking for that kinda cream-colored bone.

These go extinct 10 to 14,000 years ago.

(construction trucks driving past) NARRATOR: This road cut along a rural highway in northwest Nebraska is the latest site.

TUCKER: Nebraska would've looked a lot different 13 million years ago.

We would've had streams with very densely vegetated shorelines and some tropical forests, and we'd have had a lot different animals living in those forests, things like elephants, camels, rhinoceros.

NARRATOR: Today, Tucker is excavating with other members of the University of Nebraska State Museum, and they're expecting a visit from a road construction crew.

TUCKER: The contractor's usually a bit hesitant, but when you tell them that they're gonna still be able to work, they think it's pretty cool that they're gonna be able to take part in a scientific discovery.

CARL HART: I've got a nine mile of widening, cable guard rail, and resurfacing of the highway.

We just stop here periodically every time it rains and see if something would come up.

I do notice there is something right over here.

These pieces here.

So we'll take this over and show it to Shane.

And we are still finding pieces in this area just from this small excavation site.

TUCKER: How are you doing today?

HART: Good, back again, huh?

TUCKER: Yeah, back again.

HART: Well, we were checking on the pile for you, and it's kinda what we found when, after the rain storms and stuff.

TUCKER: Okay.

Well this is super exciting.

This is a little antelope jaw, you got part of the skull here with the teeth sticking down.

This would be a little antelope about maybe a foot, foot and a half tall, and this big one here, this is cool, this is a camel metapodial.

So basically these two bones in us have been fused together in a camel.

So that's exciting, that would be a camel, probably four and a half, five feet tall.

This shows us there's really good potential for this particular road cut to produce fossils for us.

HART: Well that's good, I hope we find a few more.

TUCKER: Yeah, I hope so too.

NARRATOR: Modern camels are normally associated with deserts of the Middle East.

But 40 million years ago, camels had their beginnings in North America.

TUCKER: Almost the entire evolution of camels occurred in North America, and so the majority of their evolutionary pathways is shown in the rocks right here in the Niobrara River Valley.

NARRATOR: This roadside dig has nearly complete remains, including jaws, vertebrae, and leg bones, TUCKER: Then in this case, to find a partial camel skeleton laid out here with the bones in life position is extremely rare.

At this particular time frame, we have three different camels, we have one that had a really long neck that would've been similar to a giraffe as far as where it was eating, we had this medium-sized camel that is the ancestral camel to all other camels and llamas that we see today, and we would've had a small llama-like camel in this time frame as well.

NARRATOR: By land bridges, North American camels first migrated to Asia six million years ago, and to South America three million years ago.

TUCKER: And they survived here all the way until their extinction in North America, roughly 10,000 years ago.

NARRATOR: Camels and other grazing animals would continue to flourish across America for millions of years.

The clearest picture of that habitat emerges in north central Nebraska's rustic Verdigre Valley.

And it tells a tale like no other.

DR. MIKE VOORHIES: I first came here in 1971.

From my map, it looked as if there was probably a cliff over here.

Ah, well, there it is.

That's kind of a thing that makes the paleontologist's heart go pitter pat, because you can actually see some bedrock.

There was still a 10-foot bed of volcanic ash looming above my head.

So I wanted to climb up and take a look.

I started taking samples of it, and I happened to notice a little piece of bone, about eight inches long.

Eventually that turned out to be the skull of a baby rhino.

Not only was there an entire skeleton of a rhino, but as we dug around, we found five more skeletons.

NARRATOR: By 1978, Voorhies' team unearthed nearly 200 complete animals in an area the size of a basketball court.

It was an unprecedented discovery.

To protect future remains, a building was constructed over the entire fossil bed.

Today, the site draws throngs of visitors to see a unique working excavation.

(chipping away at bed) Voorhies named the site Ashfall Fossil Beds.

(scraping around fossil) An entire community of animals lie in their death poses, entombed in volcanic ash, in what was once a waterhole in the vast grassland plains.

SANDY: It looks a lot like the savannas of Africa, doesn't it?

Big waterhole where animals would go every day, probably for a drink of water or to bathe.

DR. VOORHIES: As far as we can tell, this was probably the only waterhole for at least a mile in any direction.

NARRATOR: But one day 12 million years ago, life at the waterhole was upended by an abrupt event.

(explosion) DR. VOORHIES: It's almost like an atomic eruption.

NARRATOR: The eruption was from a super volcano in southwestern Idaho, far more powerful than any ever witnessed in human history.

DR. VOORHIES: So all we can do is extrapolate from the much smaller volcanoes, like Mount St. Helens, that we have witnessed.

And yes, when Mount St. Helens went off, there was this big, billowing cloud.

But less than a day later, you know, that was all gone.

NARRATOR: But the ash fall from the super volcano did not clear.

DR. VOORHIES: In fact, the air probably didn't clear up for at least weeks, maybe months after the time that the ash first fell.

Every step the animals took, they'd be kicking up a cloud of that ash.

So 24 hours a day, these animals would be experiencing slow death from suffocation.

NARRATOR: Signs of their anguishing death show up as scaly white deposits on the bones of the Ashfall animals.

DR. VOORHIES: We know from the disease on the bones that we see on the skeletons that these animals began to develop the symptoms of lung failure.

Their legs swelled up so that they had a hard time moving, they had a high fever, little ones died first, medium-sized animals died later over a period of several weeks.

NARRATOR: Trapped within the ash is an unrivaled example of evolution in action.

Five distinct types of horses are found here.

Most have three toes.

But some members of one species, pliohippus, developed shrunken side toes, while others have none, like modern horses.

This is a clear sign of natural selection at work, captured in a snapshot in time.

And there's more drama sealed within the ash.

DR. VOORHIES: And it just happened that the volcanic ash fell about a month after most of the animals had given birth.

We find lots of baby rhinos and baby horses and baby camels.

We've actually found one rhino that still had a baby inside at the time that the ash fell.

NARRATOR: Beneath the ash are tracks from the animals' last moments of life.

DR. VOORHIES: I'm very interested in what happened here.

These animals basically died in their tracks.

They became so weak and sick that at some point they toppled over, and they haven't moved for 12 million years.

NARRATOR: But a mystery remains after the ash fell.

Some skeletons are no longer intact.

DR. VOORHIES: We find good evidence that at least some meat-eating animals were still alive at least several weeks after the rhinos and horses and camels were dead.

There's a bone here that could only have gotten here by being picked up by a scavenger.

NARRATOR: And close by are the newest scavenged remains.

BROWN: Hi Kaylee.

KAYLEE: Hey.

BROWN: How are you?

KAYLEE: I'm fine, how are you?

BROWN: Pretty good.

You found a nice little critter over here, didn't you?

KAYLEE: Yep.

I actually don't really know what it is.

Do you have any ideas?

BROWN: Well, it looks...

It looks like a little carnivore, probably a dog.

The only dog that size that we know of that lived at this time was a little thing called leptocyon.

Which is probably the smallest dog that lived at this time.

And as you can see, he's maybe, at the shoulder, maybe only about eight inches tall as he stands.

See some beautiful toes here, and then the little claws.

But it is a nice little dog.

NARRATOR: Nearby is an unexpected clue that may show how this small dog leg came to rest here.

DR. VOORHIES: We're looking at the bottom couple of feet of volcanic ash.

One of these very thin layers has tracks.

This is a footprint of a big, meat-eating animal, probably a bone-crushing dog.

The carnivores had the option of going into an underground burrow, but the hoofed animals like the camels and rhinos did not.

So the rhinos had to stand around 24 hours a day, seven days a week, breathing the volcanic ash, and they died.

But evidence like this tells us that the carnivores were still alive.

NARRATOR: One mystery remains.

(volcanic explosion) When the ancient volcano erupted, it spread ash over thousands of miles.

But did the super volcano cause an extinction event?

DR. VOORHIES: You could look in any direction and there wouldn't have been anything alive probably for, who knows, several years.

But as far as we know, nothing became extinct because of the ash fall.

NARRATOR: In time, many of the ash fall species returned to this region until the climate began cooling and drying.

(truck passing by) Just two miles east of Ashfall is evidence that the climate is undergoing change.

Highway paleontologist Shane Tucker is visiting a site that the public rarely recognizes as a likely fossil site.

(boat starting up and motoring on) This pond is the core of a family gravel business owned by Curt Mitteis.

(engine starting up) CURT MITTEIS: The dredge is just a big pump sucking all the sand and gravel and whatever else is down there out.

Our waste, the sand, they use that in construction for fill, farms use it a lot for filling irrigation tracks.

Just a continuous process where you're continually moving and making lake.

SHANE TUCKER: See the yellow band, about halfway up the slope?

That's a silt lens.

NARRATOR: Although this pond is just a few miles from the Ashfall fossil beds, the sediments here are far more recent.

TUCKER: These are all two and a half to three million year old gravels that were actually eroded out of the Rocky Mountains.

This time frame is important to us.

We're starting to see the modern-day ecosystem develop.

We're long past the rhinos, things that are very foreign today.

Here the animals are probably the same species that are living today.

I love coming to gravel pits looking at these things.

MITTEIS: Shane, this is some of my better finds that I've made.

TUCKER: Usually what we're looking at is the oversized rock piles.

Quite a few treasures here in the bucket here, Curt.

Each bone, you know, has its story.

Oh yeah, this is a beauty.

This is the lower wisdom tooth from a giant camel.

This a really nice tooth.

That's a pretty large animal, too.

NARRATOR: Three million years ago, this was a grassland dominated by cooler and drier conditions.

Here, rain and wind have exposed small fossils trapped within the gravel layers.

TUCKER: A lot of times the small animals tell us a lot more about climatic conditions.

BROWN: Found something here, it's a small rodent jaw.

And so you get a pretty good indication of climate from the rodent populations.

They stay in the same place all year round.

NARRATOR: And the cooling climate is reducing the diversity of large mammals, including horses.

TUCKER: It's a... A wisdom tooth from a horse.

This is the same genus that's living today, eques, just a different species.

NARRATOR: But the best climate barometer found here is a reptile.

GREG BROWN: This is one of those tortoises.

Tortoises that aren't able to burrow can't live in an environment where there's a heavy frost or freeze, because their metabolism wouldn't allow them to survive.

NARRATOR: The conditions of the gravel pit marks the end of an era of frost-free times.

Just over two million years ago, a cooling climate would begin gripping the continent.

The onset of the ice age is evident on this farmstead near the town of Oak in southeastern Nebraska.

DR. VOORHIES: Beautiful beaver tooth.

These things live in a cold climate.

Nice.

Yeah, this is one animal that hasn't changed much in a half a million years.

NARRATOR: This ice age site was the result of glaciers advancing from Canada half a million years ago.

DR. VOORHIES: Most glaciers are like a giant bulldozer, destroy any fossil beds that are there.

The ice came within, say, 60 or 70 miles of here, but it stopped.

We're very lucky when we find a place like this, which was not overridden by the ice.

NARRATOR: Laced through the sediments are tiny climactic clues that indicate this site was once a pond or a lake.

DR. VOORHIES: There's at least 40 different kinds of snails and clams that lived in this old ice age pond.

NARRATOR: There are literally thousands of specimens, at least 150 different species, and 100,000 fossils.

DR. VOORHIES: Now that's far less than one percent of the fossils that are here in the ground.

A lot of fossils all washed together right here.

NARRATOR: But some species found here are extremely fragile.

BROWN: Oh yeah, that's a decent sized bone, isn't it?

Wow.

DR. VOORHIES: Boy, you know, I wonder if this is a bird?

BROWN: That's what I was thinking, but it's... DR. VOORHIES: Yeah, this very thin-walled and hollow, and really long and straight.

I'm just wondering if it isn't a wading bird.

Yeah, this is by far the best fossil bird site in Nebraska, of any age.

Lots and lots of ducks and herons, and storks.

That's great.

That's gonna make a good bucket.

Wow.

NARRATOR: There are so many small fossils compacted into the sediments, it would be virtually impossible to extract them individually.

BROWN: Check this out.

DR. VOORHIES: Oh, man.

Is that what I think it is?

BROWN: It is.

Big shrew.

DR. VOORHIES: Man, look at that.

It's got the teeth.

It's almost like a pair of pinchers.

Because they're really good at grabbing beetles and crushing them.

They eat mammals fairly frequently.

That's a beauty, wow.

Some of these fossils are so small that no matter how careful you are and how good your eyesight is, you would never find them just, you know, sitting here, with a scalpel.

NARRATOR; So the team is sampling the sediments by the shovelful, putting them into sacks and taking them to a nearby creek.

(walking in water) DR. VOORHIES: 99 percent of the fossils from this site were collected by washing sediment.

BROWN: These are kind of neat screen boxes, because the sides are open, so we just place them in here and let it melt a little bit.

DR. VOORHIES: You let the river do as much work as possible.

NARRATOR: Nearly 400 pounds of sediments are washed in the creek and dried on tarps.

The screened material is then taken to the museum collections lab for sorting.

The river has reduced the heavy sediments to a single box weighing just four pounds.

BROWN: Mike, I got a batch of stuff from the Albert Ahrens' site near Oak.

This is the richest micro-sediment I've ever seen.

DR. VOORHIES: Yeah.

Yeah, it really is.

Working at this site, I feel like I'm an owl 400,000 years ago looking for small things.

Half of the bones here are things that would have passed through the guts of an owl.

Yeah, there's some good-sized squirrels, almost a whole jaw of a muskrat.

The muskrats evolved rapidly during the ice age, and so we use them as an index fossil for telling exactly how old a fossil site is.

NARRATOR: While the bulk of specimens can be found by sorting, finding signs of larger species sends the team back to the dig site.

DR. VOORHIES: It has things like musk ox and moose, mammoths and mastodons, and man alive, we don't have a climate in Nebraska today that would support animals like that.

Now this part of a tooth from a mammoth, and mammoths were the largest animals in the western hemisphere half a million years ago.

Very common throughout Nebraska and throughout North America.

You can identify them even from a small piece of tooth like this.

So you can find mammoths any time in the last million and a half years.

NARRATOR: This tooth is the latest evidence that prehistoric elephants are among the region's most widespread fossil species.

DR. VOORHIES: We've got probably more fossil elephants per square mile than any state in the union.

NARRATOR: Early paleontologist Erwin Barbour unearthed 15 new types of extinct elephants to learn how elephants evolved through time.

His collection soon became the centerpiece of the University of Nebraska's iconic Elephant Hall.

DR. VOORHIES: You walk into Elephant Hall and you see these huge, magnificent skeletons, and you realize that these were actually all collected right here, in Nebraska.

NARRATOR: Behind the scenes is a vast research collection, jam-packed with ice age animals and extinct elephants.

But these remains are an unsolved mystery called Clash of the Mammoths.

DR. VOORHIES: I've never seen or read about two mammoths locked together.

It's absolutely the only one in the world that we know of.

NARRATOR: 12,000 years ago, the fatal combat took place here, a ranch in the rugged grasslands of northwest Nebraska.

DR. VOORHIES: Were you here when we loaded it onto the truck in the first place?

BEN FERGUSON: Yeah.

NARRATOR: While surveying this land in 1962, Ben Ferguson chanced upon six to eight massive fossils.

He summoned a science team for help, including Mike Voorhies.

DR. VOORHIES: We dug forward and found ribs, and there was a nice skull.

This was really pretty exciting.

Another few days of digging revealed that there were actually two complete mammoth skeletons with their tusks tangled up.

NARRATOR: To protect the remarkable find, the mammoths were shipped back to a lab for further study.

DR. VOORHIES: It's always difficult to speculate about behavior of prehistoric animals, but mammoths are so similar to modern-day elephants that I think what we've learned about modern elephant behavior probably applies to mammoths as well.

NARRATOR: Mammoths have been extinct in the Great Plains for millennia.

Now their descendants are back for a single day, just miles from the mammoth discovery site.

CIRCUS RINGMASTER: Ladies and gentlemen, please give a warm welcome to Mike Voorhies.

DR. VOORHIES: Ever since I was a little kid, I've really loved elephants.

NARRATOR: The chance to observe elephants up close is irresistible to a scientist trying to analyze mammoth behavior.

DR. VOORHIES: Look at that.

MIKE MUSTH: You can see the teeth in the back.

DR. VOORHIES: Yes.

MUSTH: Elephants are peaceful animals, and mammoths behaved a lot like modern-day elephants.

DR. VOORHIES: What an incredible tongue you have.

NARRATOR: So what was typical behavior for male mammoths?

Voorhies is seeking clues at the largest mammoth graveyard in the world.

More than 50 complete male mammoth skeletons litter a steep, cascading pit at the Hot Springs Mammoth Site in South Dakota.

KRIS THOMPSON: The mammoths that have been discovered here are young, inexperienced males.

Over 85 percent of our animals are younger than 24 years of age.

NARRATOR: During the ice age, what appeared as a feeding ground with warm waters and enticing plants was actually a lethal sinkhole.

DR. VOORHIES: This was essentially a baited trap for inexperienced young male ice age elephants who managed to get lured down into essentially a hot tub, and were not able to get out.

NARRATOR: The death of these young mammoths shows no sign of violent behavior.

So what made the entangled mammoths so aggressive?

Voorhies thinks clues lie in the behavior of adult male elephants.

DR. VOORHIES: It turns out there's one point in the life of a male elephant that they can get violent.

They go into a period called musk, which is a hormone-driven rage, and they can fight.

It doesn't really reach a climax until they're maybe in their 30's or 40's.

NARRATOR: To determine if the entangled mammoths were in this hormonal rage, Voorhies seeks help from forensic paleontologist Dan Fisher.

Fisher studies mammoths by extracting life histories from dead ivory.

DAN FISHER: Tusks keep growing and growing and growing throughout the life of the animal.

(grinding tool) NARRATOR: Fisher removes cubes of mammoth tusk to identify their age, health, and behavior.

FISHER: Okay, here she comes.

NARRATOR: Slicing razor-thin sections, Fisher is able to count the growth layers under a microscope to detect the mammoth's age.

FISHER: The darkest lines there are weeks, and the light lines in between are individual days of the animal's life.

Over the whole tusk, we can tell that this animal was about 40 years old.

That makes it a fully mature male.

NARRATOR: This tusk sample contains critical evidence that the mammoths were able to experience raging musk.

The width of the growth layers can also reveal seasonal eating patterns.

FISHER: When they're thicker, it means the animal was eating more, was healthier, growing its tusk faster, when they're thinner it means there was less to eat, or for whatever reason the animal wasn't eating as much, and the tusk was growing more slowly.

NARRATOR: But just before the deadly battle, the layers are suddenly thin.

FISHER: That's exactly what you expect in a mature musk male, because the hormones trigger a physiological syndrome that involves focusing on mating, focusing on competition, who cares about eating?

NARRATOR: Fisher's evidence shows that raging hormones sparked the mammoths to fight.

But what caused them to die locked together?

As the investigation continues, Voorhies and Fisher spot a surprising clue.

DR. VOORHIES: Wow.

This is really something unusual, but there's about a one-foot section of bone missing here from the cheek of this mammoth, and a suspicious fracture here.

FISHER: The form of this fracture is really only consistent with impact from the side.

And that would be consistent with a tusk battle, where somebody gets a left hook.

DR. VOORHIES: That's right.

A lucky punch on the cheek.

NARRATOR: But could one mighty strike really kill two mammoths?

DR. VOORHIES: Normally the tusks prevent the animals from locking heads.

But in the case of these two mammoths, each of them had one normal tusk and a stud.

That made it possible for each animal to use the single tusk as a spear for goring the other guy.

NARRATOR: During the battle, one tusk pierces an eye.

Then, a calamitous clash.

The long tusks lock over the skulls, jamming the bulls together.

But what kept them from separating?

To test a theory, Voorhies visits the fight site.

This area is normally bone dry, but Voorhies suspects that the mammoths fought on a stormy spring day.

DR. VOORHIES: My opinion is that when the badlands are wet, you can't stand, you can't drive, you can't walk around.

NARRATOR: The slick clay upended the raging bulls, slamming them to the wet turf.

DR. VOORHIES: The tusks overlapped the heads and the bodies, and they kept the other guy from getting up.

They fell in such a way that each of them had basically the full weight of the other one pressing down on him by means of the tusk.

NARRATOR; Locked together and exhausted, the mammoths died in their fallen state.

These mammoths were among the last of their species, and their deaths symbolically mark the end of the ice age.

(construction equipment) A dig of a different sort has been underway for more than a year at Omaha's Henry Doorly Zoo.

The zoo has been transforming 28 acres into a symbolic African savanna.

DR. VOORHIES: I think it's great that people have a chance to see some of the amazing diversity that has really characterized the plains for million and millions and millions of years until just recently.

Oh, she's gonna do it again.

Oh man, yeah.

(laughs) NARRATOR: But this African wildlife, like their ancestors, are at risk from changing climate and reduced habitat.

DR. VOORHIES: If you look in detail at what the fossil record tells us about climate change, there are probably two or three times more species of mammals living here 12 million years ago than there are now.

(zebra running) NARRATOR: Virtually nothing remains of the paleo world.

The only link to this diverse wildlife are the fossils found by paleo sleuths.

(serene music) Captions by Finke Copyright 2016, NET Foundation for Television (serene music) This program was funded by: The Theodore F. and Claire M. Hubbard Family Foundation, encouraging public understanding of natural history, past and present.