Roughly 13,000 years ago, Ice Age animals such as saber-toothed cats, the American lion and mammoths started going extinct in the Los Angeles basin, about a thousand years before their extinction in other parts of North America. To find out why, a team of scientists collaborated on a study that argues that wildfires due to increased human activity in the region was likely to blame. The scientists made their findings based on fossil specimens extracted from preserved remains at the La Brea Tar Pits, along with sediment cores they dug up to provide a prehistoric timeline of wildfire activity amid a changing landscape. Edward Davis is the director of the Condon Fossil Collection at the University of Oregon’s Museum of Natural and Cultural History, and one of the authors of the study, which was published in August. He joins us to talk about the study and its relevance in an era of extreme wildfires driven by climate change.
The following transcript was created by a computer and edited by a volunteer:
Dave Miller: From the Gert Boyle Studio at OPB, this is Think Out Loud. I’m Dave Miller. Roughly 13,000 years ago, big ice age animals like saber toothed cats and the American lion and mammoths started going extinct in the Los Angeles Basin. That was about 1,000 years before their extinction in other parts of North America. To find out why, a team of scientists collaborated on a new study that argues that wildfires due to increased human activity were likely to blame. Edward Davis is the director of the Condon Fossil Collection at the University of Oregon’s Museum of Natural and Cultural History. He’s also one of the authors of this new study, and he joins us now. Welcome back to the show.
Edward Davis: Thank you very much, I appreciate it.
Miller: What would the L.A. basin have been like at the beginning of the period that this study focuses on?
Davis: Well, it was a lot more forested ecosystem. So one of the things that we see in the study is a transition from more of a closed canopy sort of woodland ecosystem like you would expect to see in a cooler environment today, to the chaparral environment that’s typical for wild areas in L.A. Basin now.
Miller: What kinds of animals lived there?
Davis: Well, there are a lot of animals that we still see around today. I think it’s important to recognize that most things didn’t go extinct. But we did have a number of unusual animals that were what people think of when they go visit the La Brea Tar Pits museum, things like sabertooth cats, mammoths, giant ground sloths were present. We used to have camels. And there were even the American lion, which is my particular interest in this study.
Miller: We’ll talk more about the American lion in just a bit.
These are called megafauna in the paper. What’s the definition of megafauna? Basically, how big do you have to be to be mega?
Davis: Yeah, it’s one of those things that sounds very, very technical, but it turns out to be kind of anthropocentric. Animals that are bigger than an average human being are considered megafauna, and animals that are smaller than an average human being are considered not to be megafauna. The breakpoint is right about 100lbs. I think the average human is considered to be about 150lbs, so we’re technically megafauna. A deer would probably be megafauna, but a coyote would not be.
Miller: So the study mentions that human settlement to the region started increasing around 13,000 years ago. What’s the theory in terms of what humans were doing that may have led to more wildfires?
Davis: That’s a good question. I’m not an archaeologist, so my specialty is not in human culture and behavior. But as far as I understand it, we see that a lot of the hunter gatherer societies use fire as a way to clear and maintain ecosystems in a state that’s easier for their use. For example, here in Oregon, we know that the native peoples of Oregon maintain the Willamette as an open habitat using wildfire in precolonial times. So one of the hypotheses would be that people are coming into the L.A. basin, and they’re bringing with them a tool kit that includes using fire as a way to maintain open ecosystems that are better for hunting and gathering.
Another possibility is just that people use fire all the time for all kinds of different purposes. And when you have a higher number of people, there are more likely to be fires to get out of control. So when you’re looking at something that’s happening over thousands of years, what’s a relatively rare event becomes important over the longer time period. So part of it could have been purposeful fire setting in order to maintain ecosystems in a certain way for cultural practices. But part of it could have also just been more people around, more cooking fires, more fires for warmth at night and to keep predators away from the family. And then those fires sometimes get out of control and cause wildfires.
Miller: It’s so striking that we’re talking about 13,000 years ago, but it’s so easy just to see the modern analogs today of literally a campfire that gets out of control, or a prescribed burn that has a reason but also has other impacts on the environment. What’s the next step in this theory of causation? Why would a mammoth, say, be more likely to die out because of this increase in fires?
Davis: A lot of the thinking today about the megafaunal extinction in North America has to do with what we call trophic cascades. You can see a more positive version of it with the reintroduction of wolves to the Yellowstone ecosystem. We, as humans, had hunted wolves to extirpation (what we call it when something goes extinct locally but it’s not absolutely extinct.) So we reintroduced wolves to Yellowstone, and as a consequence, they changed the behavior of the elk, and that changed the way the trees were growing, and it ended up actually changing the river and making the river become a better habitat for salmon.
And so what we might see is that human beings are coming in, fires are increasing, and that changes the availability of certain kinds of plants in the ecosystem that were maybe important for the megafauna. You think about something like a mammoth, mammoths are grassland specialists, but they are feeding on a certain amount of grass. If the grasses are all burned away, then that produces a period of extreme loss for their main resource base. And that could actually have a major effect on them, even if they’re not being directly hunted by the humans, which may have also been happening at the same time.
A lot of the megafauna that we see going out are actually carnivores. And so part of what we think is happening is that as humans are using resources in the environment, changing the environment with fire, the resource base for the carnivores is drying up. And so they are going locally extinct, they’re extirpated, because of that loss of prey species. Some of which don’t actually get extirpated, their numbers are rarer. And so if you’re a carnivore and you depend on rare but big kills, and then those animals become rarer, then you could go extinct or become extirpated even if your prey species is not.
Miller: This takes us to the predator that you are the expert on, the North American lion. What is it? Or what should I say, what was it?
Davis: It’s extinct today, of course. But the North American lion was an important part of the ecosystem 13,000 years ago over a lot of North America. We find its fossils in California and Oregon. We find its fossils in Florida and Texas and Wyoming. And, and so what we see is that this animal from its skeleton and from ancient DNA studies is clearly related to the modern African lion, and also to the tigers of Asia. So your listeners may be familiar with this idea, but tigers and lions today are actually closely related, what we call sister species. But they’ve diverged pretty dramatically in their behavior with lions hunting as a pride, which is relatively unusual for cats. Most cats are more like tigers where they hunt by themselves and live solitary lives.
And so the North American lion is called that because a lot of people want it to be very lion-like. When you look at reconstructions, you see it standing proudly over the tar pits like an African lion. But one of the things that I’m interested in is understanding whether its behavior was actually more lion-like or more tiger-like. We look at the relative abundance of preserved animals at Rancho La Brea, and compare it to the rate that animals show up to a kill site in Africa, we actually see that the saber toothed cats at La Brea, the tar pits, seem to fill a role more like the African lions do. And the North American lion is actually rarer and looks more like some of the solitary hunting animals in Africa would look.
Miller: Is it fair to say that the saber toothed cats get more attention than the North American lions, popularly?
Davis: I mean, the saber toothed cats are much more, I guess, appealing to popular culture because they look so much different than living cats do today. The North American lion was bigger than an African lion or a tiger, but it looked like those animals. And so it’s not gonna capture the imagination the same way as a saber tooth cat does with its very different proportions and its big saber teeth.
Miller: And you say saber-tooth cat. I remember growing up hearing about the Saber tooth tiger. Is that just an old fashioned and incorrect way to talk?
Davis: Yeah, as paleontologists, we try to be very precise with our language, which is why, for example, I call it Rancho La Brea and not the La Brea tar pits, because La Brea means tar in Spanish. So we try to be precise in the language. When we’re looking at the saber-toothed cat, smilodon, we see that it’s actually not related very closely to the lion and the tiger. And so since the tiger does have a very precise name for that species, we don’t want to call it the saber-toothed tiger, we want to call it the saber-toothed cat.
Miller: So let’s go back to this paper that you were one of the authors on. What do you see as the most intriguing conclusions of this paper? What is going to be the most lasting contribution from it, do you think?
Davis: I think it’s an exemplar of the way that we’re going to be doing paleontology more as we move forward. I like to say that all extinctions are local. When we think about something like a mass extinction happening over the entire globe, we have to remember that each animal dies for its own reasons in its own spot. Each plant in a mass extinction dies for its own reasons. And so with the increase in resolution of radiocarbon dates and the improvement in lots of other techniques and looking at fossils, we’re starting to be able to look in particular places at what’s happening at that moment of extinction, and understand those local causes. And all of the local causes sum up to the global effects. Saber-toothed cats went extinct. But in the L.A. Basin, we can see that saber-toothed cats were extirpated because of an increase in fire frequency that caused a very rapid change in ecosystem. It’s probably slightly different or maybe even very different when we would look at saber-toothed cats in Florida and what might have been causing their extirpation there.
And so as we start to look across the United States and across the globe, with these better tools, we can actually put together what’s happening locally in all the different places. And then that will give us a better picture of how the extinction happens at the larger scale, which is one of my big questions that drives my research.
Miller: Another thing that stands out to me is we need to look at anthropogenic climate change, and the basic fact that as a species, we are changing the world in breathtaking and terrible ways, the scale of which is unique, it’s never happened before in human history. But I look at a study like this and it makes me realize that humans have been changing their environments in profound ways for thousands and thousands of years.
Davis: That’s another point to remember is that we have a lot of technology today that the people 13,000 years ago didn’t have. But we’re not any smarter today than they were. In fact, there’s some research that suggests the average intelligence of people was higher 13,000 years ago. And so, they’re still doing the same things that people do. They’re trying to protect their families. They’re trying to make sure that everyone has plenty of food to eat. They’re trying to make sure everyone feels safe at night. And so as people do these things, they take resources from the environment and they change the environment to make it fit them better. This is what we do.
Miller: Last week, I saw an article in the New York Times about the Pisco Basin in Peru, where a ton of fascinating fossil and archaeological remains have been found, including what’s thought to be the heaviest animal known in existence, a manatee-like whale. But the article focused on encroaching development for housing and agriculture in that area. How big an issue is this, development in places that hold such tantalizing clues about the past?
Davis: How big a problem is that? I’d say it’s one of the biggest problems facing paleontology today. A lot of concerns in paleontology have to do with the fragile nature of the fossil record that we’re using to reconstruct the past and how easy it is to lose information forever. And so you can see that places like the United States, there’s still a lot to learn, there’s still a lot of places to look and find new things in the United States. But we’ve done a lot of looking here. So a lot of places in the developing world are places that haven’t had as many eyes on them, and we’re still finding new fossils that transform our understanding of the past. Pisco Basin is an example of that.
But those countries are often places where the people have really more important things to worry about than fossils. They’re trying to survive. And so there’s this tension that develops between finding resources for people and protecting resources for fossils. In the Pisco Basin, part of what’s happening here is that it’s not the people who are in dire straits that are creating the problems. There are actually predatory developers who are going in and using the needs of the people as an excuse to essentially take land that the government wants protected, that the people want protected. So yeah, I’d say that that’s a really important problem. Fossils are a limited resource. We can never replace them, and we have to work to protect them, but also to protect all the people that are living in these areas today.
Miller: Edward Davis, thanks very much.
Davis: Thank you. Appreciate it.
Miller: Edward Davis is the director of the Condon Fossil Collection at the University of Oregon’s Museum of Natural and Cultural History.
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