Tonight on NOVA.
Millions of years ago, a cataclysmic volcano lay waste to a vast section of America.
But it also preserved hundreds of extraordinary skeletons that lay hidden for ages, until one man found them.
A glimpse of a lost prehistoric world, when animals like these roamed the American plains, buried in ash.
Music
Funding for NOVA is provided by
Merck, dedicated to pharmaceutical research, committed to discovery, improving health, extending life.
Merck
and Lockheed, America's aerospace company, supporting math, science, and engineering education for national technology leadership.
Major funding for NOVA is provided by the Corporation for Public Broadcasting and by annual financial support from viewers like you.
Music
The East African savanna, a unique mosaic of sweeping grassland, scattered woodland, and open brush.
Few places on Earth can support the stunning variety of animals found here.
But over 10 million years ago, another savanna, perhaps even richer than this one, flourished in the most unlikely of places, North America.
The ancient savanna that was once here looked nothing like today's treeless prairie.
Ten million years ago, the climate was warmer, the vegetation was richer, and subtropical animals like the ones in East Africa prospered.
New mountain ranges pushing up in North America helped create the conditions for the savanna.
Later, when the climate cooled, the savanna disappeared forever.
And yet, great geological forces also preserved a piece of the past.
A volcano that erupted millions of years ago has given us a picture of this vanished time.
Dr. Mike Voorhees has spent his career searching for the lost North American savanna.
Two decades ago, he noticed a huge exposure of volcanic ash on this cliff near his home in Royal Nebraska.
And any paleontologist worth his salt would immediately, once he saw that thing, have to climb up it and take a look at it and see what's there.
Mike followed the layer of ash around the cliff wall, ending up in this ravine.
A routine day of field work was about to change his life forever.
This is the ravine where the ash bed was exposed to.
This is the ravine where the ash bed was exposed the first time that I saw it.
And I noticed a change in the color of the rocks up here and traced the ash bed around.
And it got sort of narrow up at the top and you kind of wiggle through just about room enough for your hips.
And there was a baby rhino skull sticking out of the side of the bank up there.
In fact, the only intact skull and jaws of a rhino that I'd seen in all my years looking for fossils in Antelope County.
It was only the first glimpse of a remarkable discovery.
When Mike continued digging the next day, he uncovered not only the baby rhinoceros' full skeleton, a rarity almost unheard of,
but also found five other complete skeletons of adult rhinos.
It was time for a major excavation of the site, supported by the National Geographic Society.
As Mike and his team cleared the area, they began to realize that they had stumbled upon a mass burial site.
More than 200 animals were lying in their death poses, rhinos, camels, horses, giant turtles, and more.
The animals had died closely together in an ancient watering hole.
To Mike's amazement, the skeletons were completely entombed in volcanic ash.
He named the site Ashfall.
Well, we certainly don't associate Nebraska with volcanoes.
In fact, as far as we know, there never have been any volcanoes in Nebraska.
But, Nebraska does have a tremendous amount of volcanic ash in it.
We have been downwind from volcanoes in the Rocky Mountains for many, many millions of years.
And the Ashfall ash is just one of literally dozens of ash beds that have been spread out across the plains.
We're almost certain it came from southwestern Idaho, where there is an enormous, ancient volcanic center.
It's 10 million years old, and it has the right chemistry.
Each kind of volcanic ash has a slightly different amount of iron and uranium and other chemical constituents.
And this particular volcanic ash at Ashfall matches up very well with this volcanic center in southwestern Idaho,
which is about a thousand miles due west of here.
So that was a truly tremendous eruption.
It was something bigger than has ever been witnessed by humans, as far as we know.
One of the largest eruptions in North America in our lifetime was Mount St. Helens in Washington State.
Mount St. Helens was a pretty awesome explosion.
Large numbers of animals and a few people were killed on the slopes of the mountain.
But in context of this volcanic ash bed that we have here in Nebraska, Mount St. Helens was no more than a little puffball.
It's hard to imagine an eruption so powerful that it makes Mount St. Helens seem insignificant.
I'm walking towards the only lot I can see on top of a ridge.
I can hear the mountain behind me rumbling.
Photographer David Crockett almost lost his life when Mount St. Helens exploded in 1980.
I can feel the ash now in my eyes. It's getting very hard to breathe.
This stuff was not made for humans to breathe.
I want to live so bad.
This is hell on earth that I'm walking through.
David Crockett escaped to safety.
But for more than 30 miles from the mountain, great forests were decimated, flattened by the fury of the blast.
It seemed as if the entire landscape had been torn asunder.
The eruption also poured thousands of tons of ash across the nearby countryside.
Even 200 miles away, the drifting volcanic ash was still there.
Even 200 miles away, the drifting volcanic cloud would deposit an inch of ash.
But the ancient volcano's eruption was at least 100 times stronger than Mount St. Helens.
Its ash covered thousands of square miles, and in places like the Ashfall Waterhole in Nebraska, it was more than 10 feet deep.
What I envision happening is that the entire landscape here, for literally thousands of miles around us, was blanketed with a fall of very fine white powder.
Just imagine yourself walking across a field of snow, except that instead of snow, you've got, say, a couple of feet of volcanic dust.
Every time that you take a step, you raise a cloud of ash, and you inhale the stuff.
And I've looked at enough of this material under the microscope to be afraid of it, because it looks like a bunch of little knives.
Volcanic ash is shattered glass, is really what it is.
The animals suffocated slowly as their lungs filled with the deadly ash.
Ironically, the volcanic glass that killed them also preserved them by keeping their skeletons rigid.
Most of the animals that have ever lived have left no trace whatsoever.
It's highly unlikely, for instance, that our skeletons are going to survive for a million years.
But occasionally, nature provides us with a little remnant of something that was once alive, and that's really what the fossil record consists of.
It's sort of a tattered remnant of the procession of life through the ages.
It's the beginning of a new summer, and Mike is returning to Ashfall to continue excavating the site.
He and a crew from the University of Nebraska State Museum have set up headquarters at this farmhouse.
This is by far the most comfortable field camp that I've ever had.
We have running water, we have electricity, a refrigerator, a little tent set up with a shower in it, cottonwood trees surrounding the site, and no telephone.
Great place to be.
Mike and the crew work from sunup to sundown, using bulldozers to gradually remove the upper part of the ash bed after first probing it for fossils.
This exposes the lower portion of the bed where the skeletons should lie.
I'm more accustomed to working this stuff by the teaspoonful, so when I see somebody moving it by the houseful, I get a little apprehensive.
Without the bulldozer, this work alone would take the entire summer.
Now it will only take a few hours to scrape off ten feet of dirt to get within reach of the fossils.
Next, the team marks off a grid and digs a series of deep pits, allowing them to carefully explore the layers of the fossil bed.
The skeletons are crowded so closely together that extra care must be taken to locate and excavate them.
My brand of paleontology is fairly low-tech in the sense that we use pretty much the same methods of excavation that were used maybe a hundred years ago.
It's not as though we intend to use primitive methods, it's just that there's really no substitute for excavation with small tools, fine, soft brushes, so that we don't disturb any of the delicate fossils.
Ah, that's the sound that you want to hear. Metal on bone.
In some ways, fossil collecting is like farming. You have to have a little bit of patience. You can't expect the crop to just pop up out of the ground and be ready for you.
Like farmers, the scientists also have little control over the weather while they're working, and need to continue even when the air is full of volcanic ash.
You can't keep them cleaned off for more than a couple of seconds.
By the end of the summer, the giant grid is completed, an elaborate trench system that will allow them to plot out future finds.
There are potentially hundreds more animals buried in the ash bed. The team has just uncovered one of them, an adult rhino.
This critter with the scientific name teleoceros has always been a mystery because its teeth and its body don't seem to go together.
Normally you think of an animal that eats grass, should live out on the open plains, and it ought to have long, graceful legs.
But here it almost looks like nature made a mistake and gave it this barrel-shaped body and short stubby little legs and teeth that were adapted for eating grass.
But when you look at the hippopotamus, then the mystery is solved because there's a grass-eating animal with short legs.
Just a few feet away, they also find a baby rhino.
Oh boy, that is pretty. You know, just looking at this head though, it's kind of interesting because it's laying on its left side.
The nose is here, back of the head here, the eye would be here, this would be the cheekbone, here's the articular surface of the lower jaw.
The lower jaw comes around this way, you can see a few teeth here, and then right up in front in the lower jaw is a very, very small front tooth which shows it to be a female and fairly young.
It's a very eerie feeling to see rhinos just as they died, exhibiting that much, almost that much life and death.
You can almost feel the agony they were going through.
In some cases it almost looked like the baby rhinos were trying to nurse even after the mother had died, so it really brings up some vivid pictures for your imagination.
No animals became extinct because of the ash fall.
Every species that we have found in the ash beds so far is also found in later deposits.
So this would be more or less like a hurricane, something like that, that might wipe out animal life for maybe a few hundred miles, but it's not like a worldwide cataclysm of the type which supposedly wiped out the dinosaurs.
To prove the point, Mike and his crew leave ash fall. They travel 100 miles to the west and 1 million years later in time to a site called Plum Creek.
Here, a 9 million year old slice of the past has been exposed by the rushing creek.
If all we knew was the ash fall site, we would have a very, very interesting snapshot of one little incident in Earth history, but just as the signing of the Declaration of Independence wouldn't be very significant if we didn't know what had gone before, what led up to it, and also what happened as a result of the signing of the Declaration of Independence.
I like to put things into context, and if you're a paleontologist, the way you do that is to find as many time slices as you can.
So each summer, I like to try to add another little chapter to that calendar of events.
This is just a little, say, a million years after the ash bed was deposited, and in fact we find pieces of the ash bed in this old stream channel.
Old rhinoceros rib. What's interesting to me about this channel is that it indicates some different conditions.
A lot more water was available at this time, probably, and here we have evidence of abundant aquatic animals, fish and turtles that lived in the water, whereas at the ash fall bed, we have mostly dry land types of animals.
We find the same basic kind of rhino that might be different at the species level.
In other words, there's about a million years' worth of evolution between the ash bed and here, and in some cases the species have changed a little bit.
About as much difference as there is between, say, a coyote and a wolf. In other words, they're different species, but basically they're a similar shape and so forth.
So new species have evolved, and some species have become extinct between then and now.
So this sort of fills in some of the picture that's missing at the ash fall site.
But the area is valuable for another reason. Just a few miles from Plum Creek is Ainsworth, the home of Mike's mentor, the late Morris Skinner.
Hi, Morris. You're pretty damn good. How's yourself?
Almost as well as I am.
Son of a gun, I'm trying. Morris, you probably remember...
For more than 50 years, Skinner explored the canyons and ravines of the Niobrara Valley.
He was a world-renowned paleontologist, collecting for the American Museum of Natural History.
I'm guessing paper.
Yep, you're right.
Did you nail it?
I would say that fossils collected before the time of Morris Skinner tended to be rather imprecisely placed geographically and geologically.
Morris always made it a habit, for instance, when he visited a new locality that before he collected any fossils at all,
he would make a very accurate measurement of all the rock layers present.
It's just like a doctor might make a section of tissue by slicing through it.
Well, Morris did the same thing. He took the anatomy of a canyon and he would simply start at the bottom and walk all the way to the top of the canyon,
measuring and describing all of the layers of rock from the bottom to the top.
Then, and only then, would begin collecting fossils.
You've got to prove when that horse lived, or you've got to prove when that animal lived, and you've got to prove that.
You've got to know all those other collateral bits of evidence.
That's the point that I try to make to all these fellows, is if they collect the specimen, if they don't collect the collateral data with it, they've just got a pretty rock.
Forty-nine and a half degrees. Okay, that's off to the true north.
He's really built the foundation that a younger generation of paleontologists is using for figuring out the last 20 million years of evolution.
Just imagine trying to figure out where you are in a book if there aren't any numbers on the pages.
Nature doesn't come with numbers. Nature is not a paint-by-numbers picture.
Elevations four, two, eight.
A fossil out of context is just nothing more than a coffee table souvenir.
If you don't know where it came from, you don't really know how it fits into the great puzzle.
To find the next piece of the puzzle, Mike and his team head to an abandoned gravel pit called Big Springs.
Five miles and eight million years separate this much later site from Ashfall.
The first clues indicate that big game animals were still present at Big Springs two million years ago.
There's one, two, three, four, five zebra teeth, big old zebra toe.
There's a deer humerus, part of a zebra pelvis.
There's a bone that's been gnawed by some kind of a big rodent. It has gnaw marks all the way around the edge.
It doesn't have any rhinos, interestingly enough. So by Big Springs time, it's probably too cold or maybe too dry for rhinos.
We're not quite sure why American rhinos died out, but it's probably not a coincidence that it occurred during the time when the climate was getting cool and dry.
And so prospecting at a place like Big Springs is extremely important to me because that was just before the first ice sheet pushed its way into Nebraska.
One of the things that paleontologists like to do is to chart the climate.
The weatherman is interested in what's been happening for the last few days or the last few years.
Paleontologists are interested in what the weather was like many, many millions of years ago.
And the little critters give us probably our best key to what the climate was like in the past.
Oh, great. That's the little guy that tells you that the ice age has started right there.
That lemming is fantastic though. It's a complete jaw.
It has the first lemmings. So there were some of these little grass-eating rodents that we associate with the Arctic were beginning to find their way into Nebraska at this time.
So it's almost two ecologies are meeting at Big Springs. It's a very exciting time.
I'm always wondering what else is concealed like that around here.
I mean, there's literally thousands of miles of small streams in northeastern Nebraska and little hidden places where you've got a little peek at what's in the rocks underneath.
And one person in a whole lifetime wouldn't have a chance to see all of them.
It's remarkable that Mike has seen any of them at all. His vision is so poor that he can't drive a car. But he can see colors in low light.
I've made some of my best fossil discoveries in the evening and in the early morning.
I can't explain this because I can still find fossils, probably just because my eyes are trained to do it.
At each site, the crew hauls an unlikely bounty of treasure in large burlap sacks.
People will come down and they'll watch us standing there on the screen up to our thighs in mud.
And, well, what you doing? Well, we're cleaning the dirt.
Well, if God had intended us to clean the dirt, he wouldn't have called it dirt, I guess, in the first place.
Actually, it's very special dirt.
We're actually cleaning sediment that we know has bone in it.
And we're simply concentrating it so that we can take it back to our laboratory.
Actually, a gold miner would look for much, much smaller traces of gold in a rock than we would when we look for bones.
A tooth, all right.
Everybody is impressed by lions and tigers and elephants.
But from the standpoint of a paleontologist that wants to understand the past and know exactly what it was like, let's say, two million years ago,
if you don't have the little guys, you're missing literally 90% of the animals that were alive at the time.
And so if you only knew about the zebras and the mastodons at this time, it would be interesting.
But this puts them into context.
This is an animal called a short-tailed shrew.
This particular kind of shrew, in fact, is poisonous. It has a poisonous saliva.
So when it finds a mouse that it wants to eat, it bites it, and the mouse dies from the venom.
When you set out to look for small fossils like this, it's literally like a needle in a haystack.
And if you look at it closely with a lens, there are things of remarkable beauty, delicacy.
Not all of the smaller fossils are animal remains.
Hidden within the animal's skeletons and teeth are clues to their diet.
Mike hopes that they are the remains of plants the animals ate before the ashfall tragedy.
To find out precisely what they are requires detective work.
Fossil plant research is a specialty at Fort Hayes State University in Kansas.
Joe Thomason, one of Mike's colleagues at the original ashfall dig, is one of the foremost paleobotanists in the world.
This is from rhino tooth.
Yeah, it's from inside a baby rhino tooth.
And it looked like it might be a seed.
It is. It's a needle and thread seed. It's a really nice one.
And it's different. It's different from this material you took from a horse gut.
Okay.
That we cleaned out a little bit before. These are quite large.
Let me just bring...
Oh, it's tiny compared to the other one.
It's really small. Yeah.
It's about, you can see it's probably a fourth or fifth the size of this large one.
Now this large one from the horse gut is a described one that we described earlier from the site.
But the new one from the rhino tooth is a new one.
I don't recognize it. I haven't seen anything...
Could be a new species?
Yeah. It's undescribed. It's not...
Wow.
So that will be interesting. And what we can do is prepare both the block and the individual one for the scanner.
And we'll see some really remarkable details, some cells and different kinds of things.
Yeah.
To examine the seeds, Thomason plated them with atomized gold particles.
Electrons then bombard the specimen to create images which the scanning electron microscope magnifies thousands of times.
Well, Mike, I got that one little seed out of that baby rhinoceros loaded up in the machine.
And I suspicioned from looking at it with the microscope that it's one of these little needle and thread grasses.
Now, let's see if we can find the specimen here.
Okay. See, here it is.
There it is. Yeah.
And as we step up here, you see how it gets very rough and you see the beautiful cells come in.
And here we are up magnified about 2,000 times and we've got one of the best cells ever.
Magnified about 2,000 times and we've got one of those hook cells.
So that proves for sure that a little rhino was eating needle and thread grass.
Eating needle and thread grass.
There's none like this that I've seen from the fossil record. So this is a new one.
Could be a new species. This is a new one.
Oh, fantastic.
The discovery of ancient grasses is further proof that the savanna first appeared in North America, long before it arose in Africa.
In both environments, grass became the staple food, giving rise to similar animals specifically designed to eat it.
The zebra is one of those grass-eating animals that evolved in North America first.
Another is the ancestor of the modern horse.
When we learned about history in school, we were taught that the Spanish brought the first horses into America.
But I think that's where paleontology can fill in some gaps in the record.
It's certainly true the Spaniards did bring horses into America, but that 50 million years before that, we certainly had horses here in America.
And right here in Nebraska, there's a 50 million year record of horse evolution.
So in some ways, this was the sort of the proving ground or the evolutionary cauldron from which these grass-eating species evolved.
There are few opportunities in paleontology to examine a species as it evolved at a specific moment in time.
But in 1979, Mike's crew uncovered a unique treasure at Ashfall, 70 skeletons from five different species of horse.
The find itself was a rarity, but even more unusual was the discovery that some horses had three toes while others in the same species had only one.
We had some horses here that, at least in terms of the anatomy of their feet, were indistinguishable from modern horses.
But the very interesting ones are the ones that are sort of passing through a phase.
There should be some evidence of a transition from the tridact or the three-toed stance to the modern one-toed stance.
And up until now, that has never been available in paleontology.
There's the side toe, let's see. Oh yeah, this one has a well-developed side toe.
So, this one is not the ancestor of the modern horse.
By this time, the ancestors of the modern horse had already either lost those side toes or they were extremely small.
Yeah, I think anybody that doesn't believe in evolution ought to have a chance to get their nose down close to the horse.
Anybody that doesn't believe in evolution ought to have a chance to get their nose down close to specimens like this.
A hundred years ago, when three-toed horses were first discovered in the Niagara Valley,
this was some of the first and some of the best evidence that paleontologists were able to come up with in testing Darwin's theory.
We tend to think we know what horses are, but ten million years ago you'd have to ask, well, which horse are you talking about?
We had horses living in Nebraska at this time, ranging in size from, say, collie dogs up to the size of a Shetland pony.
Some of them had short stubby legs and lived in forests, and some of them were built like gazelles and lived out in the open plains.
Prehistoric horses thrived in North America until 10,000 years ago, when the last Ice Age and human hunters led to their extinction.
But a crucial part of their evolutionary past still survives at Ashfall.
To protect the fossils still being uncovered at the site, Mike and his team have planned a new state park with a building that will surround the exposed skeletons in the ground.
This one will be.
With its hind end in the building?
Right.
The baby should have its head in the building, I think.
Well, that's the way it looks.
This particular footing may represent a bit of a problem.
We may have to dig underneath the skeleton to pour the cement into this spot.
We had intended to put the wall here of the building. Of course, we didn't know what was underneath, so we dug this trench out to find out and hit this horse, and a rhino, and another rhino, and a baby rhino.
Actually, this spot I'm standing right here is from another rhino that extends in here.
There are just so many bones that had to shift the building over a little bit to try to get these inside.
Where the wall is now, it looks like there won't be anything beyond that, or very little.
So we've got the building situated over the best possible fossils right now.
And I think one thing I like about it, it's going to look like a barn. It will fit right into the landscape here.
So the rhino will be tucked in for the winter.
Not all of Ashfall's fossils will be kept in the barn. A few are needed as museum exhibits for the park's visitor center.
These will have to be reassembled from skeletons collected at Ashfall a decade earlier.
Most people are familiar with going into a museum and seeing a full skeleton standing before them.
Most people don't realize that most of those skeletons mounted in museums were probably not found as a single skeleton.
Many of them would be painstakingly reconstructed from bones that originally were from many, many different animals of the same species,
and they were found mixed together in a bone bed. Now there's nothing illegitimate or necessarily misleading about that approach.
That's the way paleontologists have traditionally carried out their craft.
Since I was a little kid I wanted to get up and touch his teeth. Here they are.
Most skeletons, mounted skeletons that you see, were not found complete.
I had never seen a full skeleton of any of these species before.
You almost have to use a hippo model to get a living animal that looks like these things.
It doesn't look right. If I hadn't known what these things looked like I'd say you got the wrong ribs.
Right, right, right. If you didn't collect them together.
One of the very unusual things about Ashfall is that we do have absolutely complete creatures.
Using the skeletons as guides, Mike and museum artist Mark Marcuson begin work on a mural depicting the Ashfall tragedy for the visitor center.
There was always a certain amount of guesswork into the body shape.
So when Mark Marcuson came down to our lab and he was about to begin on his project of painting an Ashfall scene,
we were able to haul out the skeletons and take detailed measurements on them.
I think we all know what a modern horse looks like and what we'd like to know is what these little bitty three-toed horses looked like.
This is a fascinating little horse. Back in 1857 they found one tooth.
This is the original specimen of this little horse, Sudaparian, and for many years that was all there was.
And then Morris Skinner found some skulls and jaws. He was able to match up this tooth with some skulls.
And now at Ashfall we've got whole skeletons. We've got a whole herd of skeletons of this little Sudaparian.
So you'll be the very first artist that's ever attempted to show what Sudaparian looked like in the flesh.
Let's get an idea of what the camel looks like here.
It's shaped a lot like the skull of a modern camel.
I've got the first three vertebrae in the neck here, and these are very, very similar to llamas, modern-day South American llamas.
So in many respects, I think, for trying to figure out what they looked like when they were alive, a llama is a pretty good model.
These are some of the most unusual things we find in the ash bed are birds, and this is an almost complete crane.
This is the cartilage from the trachea, isn't it?
Yeah, the actual cartilage is still there.
There's the neck curving down under the body.
These would be really similar to a crown crane, right?
Right. Yeah, apparently the closest living relative is the crown crane of Africa.
You start, first of all, with the skeletal structure, and after you are able to draw that out and put it together on a piece of paper,
then you can go back in with information gleaned from the modern animals, their closest living relatives.
With the five different horses that we have up at Ashfall, we decided to pick three for the mural,
and I had to decide, well, how are we going to make these horses look different from one another?
So on one of them that looked a lot like a zebra in terms of it to build,
I chose to use variation on a zebra theme for the stripes and the color of the coat.
So the idea is really to see what you can come up with, but still to have it look realistic.
But in terms of the actual structure and the look of the animal,
we think we can come pretty close to what they actually look like.
So what I'd like is to have the map like that, and then have Gale print out giant turtles then and now.
Let's see if we can get him over on his belly. Okay.
Looks good at the foot. Oh, this looks great.
I'm going to have to adjust the front leg here so that the sole of the foot is flat on the ground.
Even the sole of the foot is totally covered with armor plates of bone.
It would be like walking around in chain mail.
The fact that you find them in the rocks in Nebraska, I think, tells us that we had a frost-free climate when they were here.
So when do we last see these in Nebraska?
The tortoises last until we get our first evidence of glaciation in northeast Nebraska, and then they're gone.
It's a completely different place.
Can we go through there?
We'll have to find out, aren't we?
Nope.
Nope.
That's everything we need to have a tourist attraction right here.
Only days remain before the park's grand opening.
The scene inside the barn is a sober reminder of the tragedy that occurred here.
Complete skeletons of rhinos and horses are intertwined.
Off to one side lie disembodied camel jaws and scattered ribs,
a testament to the animal's painful death.
Well, in science, you're not supposed to read into scientific specimens any human qualities.
But I must admit, I try to empathize with the animal.
It's hard not to do that when you've got a whole skeleton.
I think it helps me in my scientific study to observe them just as closely as I would observe another human being
and look for those little signs that, okay, this one is different from this one.
This is not anthropomorphizing.
I think it's just getting in touch with the realities of your science.
One sign led to an important discovery.
White bone deposits prove the animals suffocated for days.
Oh, this is ugly. Very, very heavy Marie's disease right there.
This animal probably had the lips pretty well swollen just before it died.
It's like an inflammation.
The bone becomes inflamed and the soft tissue around the bone balloons up.
Gosh, what would be a good example?
Well, if you've ever sprained your ankle, the blood rushes to the area and the thing swells up.
I'm just trying to imagine what they looked like when they were swollen up.
I'm not sure I want to think about that.
Most of the complete skeletons are of rhinos.
The females outnumber the males seven to one.
Within the herd are signs of life within death.
This female was pregnant when she died.
The evidence? Two small cartilage-like bones from the fetus.
We think that the rhinos probably lived in a big herd.
There's a little head and a skeleton here of a baby rhino.
Right next to it we think is its mother, so they're almost touching noses.
We think we can figure out that that one is the mother of that one.
So it's kind of sad to think that they all died together.
The female rhinos and their calves were part of a single male's harem.
The telltale front teeth reveal their sex.
Males have larger ones.
While most of the rhinos had near-perfect teeth, one of the males had an unusual problem.
This thing extended out into a point because the lower tooth,
which should have ground against it, wasn't there.
The lower tooth maybe never developed or perhaps was knocked out in a fight. Who knows?
Sometimes I wake up at night thinking about what would have happened
if the glaciers had come another five miles west of where they did.
Probably this entire unique fossil bed would be gone.
The glacial deposits in Nebraska cover about the eastern quarter of the state.
Just a little more glacial ice and this site would have been bulldozed away.
Opening day finally arrives in June.
After nearly a decade of field work, visitors get their first glimpse of the Ashfall tragedy.
In a public setting like a park, potentially we can reach thousands and thousands of people.
If maybe five or six kids come out here and can learn something at Ashfall Park,
they can learn that there are scientific discoveries out there
that they themselves can make. Not everything has already been discovered.
How come they all died in one place?
Well, we think that they were coming here for water.
These bones, actually as they were, it's remarkable they don't seem to be petrified at all.
We almost never get this kind of evidence about how the animals lived and how they died.
Visitors can ask questions of the scientists at work.
Here, someone wonders about a leg bone lying on top of a skull.
When we see this, it's always on the part of the carcass that has the best meat.
And we actually think that that was pulled out of there by a big meat-eating animal.
Now, we're still looking for the skeleton of an animal that's big enough to tear the hind leg off a rhino.
We haven't found it yet, but we suspect that somewhere in the ash bed
we're going to find either a big, maybe a bear dog or a saber-toothed cat.
To me, the fun of a park like this is that we're going to leave them here in the ground
so everybody can come down and make up their own mind.
So in this case, we don't have to resort to any sort of trickery at all.
I mean, we're going to leave them just exactly the way we found them
and leave them here for future generations.
You know, they might be smarter than we are. I hope they are.
And they can come up with their own ideas.
At times like this, for the last ten years, when I see a dark cloud like that coming,
I always think about that big cloud that came in ten million years ago.
It's hard not to be really overwhelmed by the power of nature.
If we don't have some appreciation for our natural heritage,
some sense of wonder and awe at the world around us,
we're reducing ourselves to the levels of unintelligent savages, I think.
I'm convinced we haven't found the whole secret here.
We're still waiting for our first elephant. We're still waiting for our first saber cat.
I think around the next bend in the water hole, we could get a whole new group of critters.
So that's what keeps us going.
A production of WGBH Boston.
Funding for NOVA is provided by Lockheed, America's aerospace company,
supporting math, science, and engineering education for national technology leadership.
And by Merck, dedicated to pharmaceutical research, committed to discovery,
improving health, extending life.
Merck.
Major funding for NOVA is provided by the Corporation for Public Broadcasting
and by annual financial support from viewers like you.
This is PBS.
For a transcript of the NOVA program you've just seen,
send $5 to this address or call 1-303-8319-000.