Ice Age Co-Stars: Horses, Camels And Cheetahs

Matthew Kohn
Distinguished Professor, Department of Geosciences
Boise State University
Boise, Idaho

Christopher Hill
Associate Dean, Graduate College
Associate Professor, Anthropology
Boise State University
Boise, Idaho

Mammoths and saber-toothed cats may be the most famous beasts of the Ice Age. But they shared the prairie with horses and camels, too—both of which evolved in North America and crossed the ice bridge into Eurasia, before disappearing here. Matthew Kohn and Christopher Hill talk about the lesser-known fauna of the Ice Age.

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IRA FLATOW, HOST:

This is SCIENCE FRIDAY. I'm Ira Flatow. We're broadcasting live from Boise, Idaho. And Idaho, you may not know, is not only famous for its potatoes. Just a couple of hours from here are the Hagerman Fossil Beds, where the skulls and skeletons of hundreds of early horses have been dug up. These fossils are the earliest known examples of the equus genus, relatives of today's zebras and horses and donkeys.

And that's right - horses evolved here in the grasslands of North America before going extinct here also. But they weren't alone. There were a lot of unusual creatures roaming around North America during the Ice Age, ones you don't hear much about, as much as the mammoths and the saber-toothed cats.

Did you know that camels lived here too, alongside supersized bison, American lions that are bigger than the African lions, and cheetahs. And this is safari-quality stuff. But you'd have to be a caveman to have gone on safari in those days because many of those large beasts disappeared around 10,000 years ago, just as humans were entering upon the scene.

Were they hunted to extinction? Where did they go? Killed off by disease? Or could the culprit have been then climate change also? And why did most of the large mammals die out where the small ones lived on to modern-day time? Just a few of the mysteries about our North American fauna, and that's what we'll be talking about for the rest of the hour.

We won't be taking calls today, but if you're here in the audience, I invite you to step up to the mic and ask a question. You can also tweet us @scifri at S-C-I-F-R-I, and go to our website at sciencefriday.com, where you'll find links to the topic, and you can leave a message also.

Let me introduce my guests. Matthew Kohn is a distinguished professor in the Department of Geosciences here at Boise State University. Welcome to SCIENCE FRIDAY.

MATTHEW KOHN: Thanks Ira, pleasure to be here.

FLATOW: You're welcome. Christopher Hill is associate dean of the Graduate College at Boise State University. He's also associate professor of anthropology here. Welcome to SCIENCE FRIDAY.

CHRISTOPHER HILL: Thank you, Ira.

FLATOW: You know, this is - this I think is certainly knew. When we were talking about topics we were going to talk about when we came to Boise, is talking about the menagerie of animals, Christopher, that were here at one point. You always hear about the mammoths and the saber-toothed cats, but there's a whole lot of other stuff like camels here.

HILL: Sure, there were both plant-eaters like camels and bison. Down in Idaho we had musk ox and caribou. So there were a lot of plant-eaters, and then there were meat-eaters like saber-tooth cats.

FLATOW: So you mean the camel was here before it was out there in the desert in another continent in the Middle East?

HILL: Sure, the camel evolved in North America. It started off as something about the size of a rabbit about 20, 40 million years ago, and over time the population's changed, and it became even larger than the kinds of camels we see today. So there were gigantic camels for a while.

And then around 11,000 years ago camels disappeared in North America.

FLATOW: Did they go someplace?

(LAUGHTER)

FLATOW: I mean...

HILL: They became fossils.

FLATOW: They became fossils, and you have found those fossils of the camels.

HILL: Yes, so we found examples of camels in Southern Idaho and in Montana, and they're connected with all these other animals you were talking about.

FLATOW: Did they evolve into the camels that you see in other parts of the world?

HILL: Sure, so they spread across probably from Alaska to Siberia and into Asia and then became the different types of camels we see all over the world.

FLATOW: Wow. Matthew Kohn, you've studied the horses from the Hagerman Fossil Beds. Tell about that. It must be very exciting. You found a lot of stuff in that bed.

KOHN: Well, one of the things I do, my specialty is really in stable isotope geochemistry.

FLATOW: What?

KOHN: Stable isotope geochemistry. And so what we do is we analyze the ratio of stable isotopes of oxygen and carbon to learn something about the ecosystems and the plants that were living in the area at the time. So what we analyze are scraps of tooth enamel, and they're tooth enamel from these different animals that lived here.

Some of them are from Hagerman horse. There were also some camels, mastodon. We've analyzed some beavers as well.

FLATOW: And these are all found in this one spot? What makes that spot so special that all of these fossils were found?

KOHN: Well it's one of the more fossiliferous localities in the...

FLATOW: We keep doing these F-things, I'm going to run out of...

(LAUGHTER)

FLATOW: Why would they be all there in that one spot?

KOHN: Well, those particular kinds of sediments turn out to be quite fossiliferous. Hagerman has an extremely well-exposed sequence of sedimentary rocks. They're all about three to four million years old. And there is one particular locality, the Hagerman Horse Quarry, where hundreds of horses were discovered, their fossils were discovered back in the late 1920s, early 1930s.

FLATOW: And how does the Hagerman Horse fit in with the modern horses and zebras of today?

KOHN: Yeah, it is the earliest representative of the genus equus. So you have to think about horses. There used to be many, many different genera of horses across North America. There are individual localities in - from about 14 or 15 million years ago, where there will be seven or eight different genera of horses, not just species, but these are the actual genera, whereas today we only have one genus, the genus equus.

So these genera evolve, and over time the genus equus evolved. Hagerman is the earliest representative, as far as I know, of the genus equus, and from that genus then spread out all of the different species of equus.

FLATOW: So the big mystery, we had the horses, we had lions that were bigger than lions in Africa, Christopher?

HILL: That's right.

FLATOW: Giant lions, how big?

HILL: About 20 percent bigger than the African lion. And there were other kinds of large cats.

FLATOW: Such as?

HILL: There was a saber-toothed cat.

FLATOW: We call it the saber-toothed tiger, right? Is that a...

HILL: Please don't say that.

(LAUGHTER)

FLATOW: I won't say that.

HILL: So there's another saber-toothed cat called homotherium, and we've found examples of that. And besides the American lion, there's also a puma, but it looks sort of like a cheetah, so it's sometimes called the American cheetah.

FLATOW: And they all disappeared about 10,000 years ago, and that's the big mystery of where they went - they became fossils - and what happened to them. And your theory is about what happened.

HILL: Well, it's an important experiment we have in the natural history to look at these examples of animals that went extinct and to try to figure out what might have been the reasons why they went extinct. And the two big reasons, usually, that are discussed are either changes in the environment, like global warming events or global cooling events, or also predation, like..

FLATOW: Hunters.

HILL: Hunters. And one example of that would be over-hunting by humans.

FLATOW: These were the Clovis people?

HILL: In North America, the old Stone Age people that lived right at the end of the Ice Age are called the Clovis people, based on an archaeological site in Clovis, New Mexico, where the first spear point was found with mammoth, mammoth bones.

FLATOW: Would it be that they suddenly learned how to be better hunters?

HILL: Well, so one argument is that there was a human population, a small human population here, maybe before 11 or 12 thousand years ago, but they didn't know how to use spear points to hunt these large animals, and then around 11,000 years ago that population learned how to use spear points, these large spear points, to hunt the animals.

FLATOW: Matthew, you were shaking your head about all of this.

KOHN: Oh, absolutely, yeah. Those are the two hypotheses: rapid climate change, changes in the environment or ecosystems, and then over-hunting by humans. I should say not all of the large animals went extinct, right? We still have deer, we still have moose, we still have antelopes, and they lived back in the same time period that all of these - you know, we consider them exotic animals - were living here too.

FLATOW: The bison were living back then, right? Why didn't they get hunted for extinction if they were hunting?

KOHN: Well, we almost did, didn't we?

(LAUGHTER)

FLATOW: Well, that was just 100 years or so ago, right?

KOHN: Well, that's true.

FLATOW: But they were a little heartier, maybe, Christopher?

HILL: There are some examples, or many examples, of bison kills connected with a time right after Clovis, called the Folsom Period, around 10,500. And that was - most of those sites connected with Folsom are connected with bison, whereas Clovis sites are connected with mammoths.

But the bison is an example of an animal that probably came to North America between two and one hundred thousand years ago and then survived in different versions until about 11,000 years ago. So it went through different climate change episodes, and then right around 11,000 years ago, apparently there was a bottleneck, a decrease in the population. The numbers of bison and all the bison that live in North America now are from a group that was a fairly small group that almost went extinct around 11,000 years ago.

FLATOW: Quick question before the break, yes.

UNIDENTIFIED WOMAN: Ira, I think you're wonderful, first of all. Thanks for coming to Boise. Can families take their children to Hagerman to see the fossils that you have explored?

HILL: You can certainly go to Hagerman Fossil Beds, and you know, it's a public area. You can walk around. But in general, the fossil localities themselves are not open to the public. And in general, all federal lands are prohibited from vertebrate fossil collection. Private lands, of course you talk to a landowner, but federal lands are generally protected.

FLATOW: We have a tweet coming in from Jado(ph), who says: Don't forget about the giant ground sloth, the short-faced bear and the giant armadillo. Those are - we're not forgetting now.

HILL: We've analyzed them.

(LAUGHTER)

FLATOW: How big were these animals? Were they bigger than the kind we have today, or are they...

HILL: Ground sloths are, what, seven feet tall?

KOHN: Yeah, there was a ground sloth called Megalocnus that was found at Hagerman, and it was probably seven or eight feet tall, and it was probably one of the smaller of the ground sloths. And a version of that ground sloth also went extinct around 11,00 years ago.

An interesting thing about the ground sloths is that their - we were talking earlier in the previous hour about what is native and non-native, what would be an exotic animal. This is an example of an animal that would - originated in South America and migrated into North America.

And there are other examples of that also. A living example would be a porcupine. It's an example of - the ancestors of porcupines came from South America. On the other hand, we were talking about bison, and they are also an exotic animal if you look at geologic time scales.

They came to North America between two and one hundred thousand years ago.

FLATOW: Wow. All interesting stuff. We're going to take a break and come back more - and talk more with Matthew Kohn and Christopher Hill, and questions from the audience, talking about the lions and tigers and - no tigers. No more saber-toothed tigers. We're not going to call them that anymore. So we'll be right back after this break. Stay with us. I say, we'll be right back. Don't go away.

(APPLAUSE)

(SOUNDBITE OF MUSIC)

FLATOW: This is SCIENCE FRIDAY. I'm Ira Flatow. We're talking this hour about the beasts of the Pleistocene, like mammoths and camels and early horses and why they suddenly disappeared about 10,000 years ago. My guests are Matthew Kohn, distinguished professor at the Department of Geosciences; Christopher Hill, associate dean of the Graduate School, all here at Boise State University.

Our number is 1-800 - but we're not going to take calls today. We're going to take calls - hopefully - people stepping up to the mic here. Let me ask you, Matthew, as we begin: This must have happened - if there was a climate change, this must have happened over a really short period of time, did it not? What would be the estimate on that?

KOHN: Well, it's interesting because when we talk about climate change on the Earth, there are different parts of the Earth that respond more or less rapidly. So when we look at places at high latitudes, they respond very quickly to climate change. We see that today, that the arctic is responding very quickly to global warming.

When people have looked at the Greenland ice cores, they have found evidence for climate change that is very rapid, this is the transition from the Glacial Period into the warm period of the Holocene, on timescales of decades or even less than decades.

Now, once that occurs, there's a huge ice cap over North America, it takes thousands of years for that ice cap to disappear. So there's some parts of the climate system that respond more slowly, but there are other parts that are very sensitive, and they respond very quickly.

FLATOW: Yeah, we're watching the Arctic respond very quickly these days.

KOHN: Exactly.

FLATOW: Let's go to the - let's go to the audience here.

UNIDENTIFIED WOMAN: To the question earlier, we took our children to the Hagerman National Fossil Beds Visitor Center, which was really interesting for them. They became junior rangers. But a ranger that was there explained to us that the majority of the fossils they found of the Hagerman horse all died at the same time. And so I had questions if you had theories as to how they died.

KOHN: Yeah, so the Hagerman horse fossils, I mean we're talking about a single quarry that - where over 200 individuals were excavated, mostly as skulls or jaws but also some complete skeletons. In general, these deposits are called bone beds, and they're really two different kinds of generations of bone beds.

One is a gradual accumulation - for example, a watering hole that might have animals that accumulate every year until finally you have a lot, or you can have a catastrophic event. And the theory, the prevailing theory for Hagerman horse, those horse fossils, is that it was a catastrophic event - for example, a flash flood that could've taken out a herd of horses.

Or they could've been killed upstream and washed downstream and deposited in that location. But it is viewed by most people as a catastrophic accumulation.

FLATOW: Thanks. We have a tweet poured in from MichaelDeGraff(ph), who says: To the lady who wanted to show your kids the fossils, please take your kids to the National Park Service Visitor's Center at Hagerman, so you can get - I'll go here and I'll come back here. Yes, ma'am.

UNIDENTIFIED WOMAN: Going back to the Pleistocene overkill versus climate change hypothesis, Matt and Chris, it seems - I'm not a hunter, but it would seem pretty to take out a seven-foot sloth, but maybe not so easy to take out a giant cat. So did the cats go extinct because they lost their prey, or were people actually maybe hunting them?

HILL: You know, there aren't any examples that I know of where we have evidence of people hunting the carnivores, like the saber-toothed cats. But there is an example where one of the saber-tooth cats, homotherium, we found a den that contained lots of examples of baby mammoth teeth in that den. So it's an example where the homotherium, that ancient cat, probably went extinct not because of over-hunting but because its prey went extinct, and that's one example that we have of that.

FLATOW: Was it a scary time to be a person? We've got these - all these big animals that might be coming after you...

KOHN: Ira, maybe it was a delicious time.

(LAUGHTER)

FLATOW: No beer. No...

(LAUGHTER)

FLATOW: Yes, ma'am.

UNIDENTIFIED WOMAN: With the advancement of technology, can you evaluate multiple evidences at the same time and create a probability of one theory versus another theory more easily than maybe 10 or 20 years ago?

FLATOW: Christopher?

HILL: Well, there are lots of different ways we could kind of try to answer the questions about over-hunting or climate change. And some of them are - we find bones that we can't identify based on what they look like. And it might be that we could use techniques like DNA to test those bones to see if they're actually extinct animals or animals that still persist today.

Another big question when we're looking at the different models, the different ideas connected with extinction, is the timing. Do we have people there before or after the extinction event? And today we have much better precision in terms of being able to estimate, measure and estimate the timing for extinctions.

FLATOW: Would there be enough people around at that point to wipe out all these animals?

HILL: Well, that's a good question. I think there were very low numbers of people at that time. So one idea would be that overkill was a contributing factor but not the only factor that combined to lead to the extinctions at the end of the Ice Age.

FLATOW: OK, let's go here, and then I'll come back here, yes.

UNIDENTIFIED MAN: So I'm curious what it takes to identify a new species from the fossil record. It seems like in the past, you know, somebody will find a fragment of a skull and declare it a new species. I'm wondering what's the threshold. Do you need an entire skeleton? Do fragments count? How does that work?

KOHN: Most species - genera and species are identified based on tooth morphology, and that's largely because - well, for a couple reasons. One is it's distinctive, and so different species have different crenulations to their tooth enamel and so on. But the other thing about teeth is they're incredibly well-preserved.

So they're very resistant to physical abrasion and to chemical decay, and so that's one of the best materials that we have. It's not the only thing that is used to identify different species, and so the morphology of the skull and the shape of the limb bones is also used, although the limb bones and body bones, generally called post-cranial material, is generally less well-preserved than the skull material.

FLATOW: Before - you want to follow up?

UNIDENTIFIED MAN: Well, I just was going to say I'm a dentist, I just happen to be a dentist, and I see tons of different morphology in teeth in humans. I don't know if that's different from other species, but it's just a coincidence.

FLATOW: They could use you over there at the dig.

(LAUGHTER)

KOHN: But it's also true, there is internal variability to any tooth morphology that one might be willing to assign to a particular species. So it has to be a morphological feature that exceeds some threshold that is identified by looking at populations of teeth.

FLATOW: OK. Yes, sir.

UNIDENTIFIED MAN: Hi. I was glad to hear you say that hunting was a contributing factor because I'm a retired science teacher, and I remember before plate tectonics came in, I was starting to teach. And then plate tectonics came in, and it started to explain things. And they had that theory about everybody running across the land bridge, slaughtering animals and populating North America.

UNIDENTIFIED MAN: And then they figured out that you'd have to have tribes of people every few years picking up and moving down to make that happen. And so my question is: You know, as we find more and more evidence, like Kennewick Man or like other spear points, not just in Clovis, New Mexico, but on the Eastern Seaboard, maybe near New York, and they find these things around, how does that register for you as a teacher, professor and a scientist, in changing how we view the theories that we once purported as being the best theory, and now we've got to move on because it's obvious there's new evidence.

So how do you guys address that? That's my question.

HILL: Well, the great thing is we're getting more and more information. We're getting larger samples and samples that we can study in a lot more detail. So you're right. I think if we were in a radio show 20 years ago, we would talk about Clovis, and Clovis would be the first real good example of people in North America.

And today, with more discoveries, there are some possibilities of older things, older than Clovis. And that would then connect with the question of extinction. If there are already human groups in North American prior to Clovis, why didn't they cause the extinction? So there are all these new discoveries that then lead - help us test our explanations, test our hypotheses.

FLATOW: We were a radio show 20 years ago and did talk about Clovis.

(LAUGHTER)

FLATOW: Apologies to the audience. We've run out of time for this segment. We're going to thank you both for taking time to be with us today, and it was very interesting, talking about all the species that have become extinct. And thanks again.

HILL: Thank you.

KOHN: Thank you.

(APPLAUSE)

FLATOW: Matthew Kohn, Christopher Hill from Boise State University.

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