Prof. Larisa DeSantis
Appearances
The Ancients
Ice Age Australia
You had quite a diversity of different types of kangaroos, some kangaroos that were eating different types of vegetation that I'll talk a little bit more about, but is a type of vegetation that's difficult to eat today, primarily because it has lots of salt. The saltbush has salt and requires you drinking a lot of water.
The Ancients
Ice Age Australia
And so that's a resource that a lot of different animals also exploited then that likely are unable to exploit that resource to the same degree.
The Ancients
Ice Age Australia
Koalas used to be much more diverse. And so that's one thing that's really interesting to look at and why I believe koala conservation is so important is because in the past, we had many more different types of species during the Miocene, which is an older time period.
The Ancients
Ice Age Australia
So before these ice ages, you had much larger koalas as well, but you had this enormous diversity and that diversity has largely been cut short with these various extinctions or even just how environments have changed over time. You know, Australia is a story about aridification. So we often will zoom into the Pleistocene and look at the short-term impacts of aridification.
The Ancients
Ice Age Australia
And honestly, that's what drew me to working in Australia. I worked in Florida looking at effects of glacial and interglacial periods. And I really wanted to know what happens when an environment is really stressed to the max. Right. When you have extreme aridification and that's Australia. But Australia has also undergone aridification over millions of years.
The Ancients
Ice Age Australia
So it it was largely sort of a more of a rainforest world earlier on. And, you know, slowly it sort of begun to dry out and reduce the forests. But there used to be forests in, you know, areas that today are, you know, semi arid regions. And so you've you've seen this transition over millions of years going from things like possums in the treetops or actually giant, you know, wombat like animals.
The Ancients
Ice Age Australia
There were things related to diprotodons kind of from that sort of group that were up in the trees, kind of like a maybe like a sloth bear or a panda bear. trying to get at, you know, fruits and in a very wet, lush environment.
The Ancients
Ice Age Australia
And then as things begin to dry out, and this is something that's happening sort of also globally, you know, one of the big events is, you know, Australia, Antarctica and South America were all connected at one point. And you have the unzipping of these continents.
The Ancients
Ice Age Australia
And ultimately, when you isolate not just Australia and South America, but also Antarctica, and you begin to have ocean circulation that's just circulating around Antarctica, you have that cold water that's sort of allowing for these cold environments and therefore the buildup of glaciers and ice. And that's actually... contributing to sort of global cooling, right?
The Ancients
Ice Age Australia
Before that sort of water was sort of directed, you know, up into other areas, you'd have warm water making it into these cooler areas. And much like, you know, today you can have palm trees in some parts of England, right? Because of the Gulf Stream coast, you had other sort of phenomenon that were keeping parts of these areas very warm.
The Ancients
Ice Age Australia
And when you have this separation, we think, from South America and Antarctica, and you tend to have the increased ocean circulation, it gets much colder. And we see these effects across the world, right? We get opening up of grasslands in places like North America or the Americas in general. You get some giant, really bizarre animals on the landscapes.
The Ancients
Ice Age Australia
in these big grassland, more open woodland environments, as opposed to the rainforest that had sort of predominated previously. And we often refer to this shift as kind of going from like the greenhouse world to the ice house world. So, you know, Australia exemplifies all of these changes and there's all sorts of amazing animals.
The Ancients
Ice Age Australia
And I think part of the reason you get such iconic and unique animals is largely because these animals evolved in isolation for such a long period of time.
The Ancients
Ice Age Australia
There were. You know, it's interesting because that's something that you wouldn't necessarily expect to get a lot larger. We expect reptiles to get larger when it's warmer. And interestingly, though, there were some really large pythons essentially that lived in Australia. And so imagine something a bit bigger than an anaconda.
The Ancients
Ice Age Australia
not quite as big or not nearly as big as, you know, the Titanoboa, which is a Paleocene or aged snake that's from South America. You know, that's when it was really warm and these snakes could get really, really large. But it is a pretty massive snake, you know, for the time, especially, and is found in a few sites in the southern part of Australia. Yeah, I wouldn't want to be near it.
The Ancients
Ice Age Australia
Although I will say I would take a python over a venomous snake any day. So the big snakes are actually not the ones to be as afraid of. They're the ones that are usually not venomous. The venomous ones can be, you know, those are the ones I'm terrified of.
The Ancients
Ice Age Australia
Yes and no. There are a fair number of sites in Australia that preserve megafauna, but there are far fewer that demonstrate coexistence of humans and megafauna. And there are really none that show sort of direct evidence of humans killing, say, like a diprotodon or one of these really large animals.
The Ancients
Ice Age Australia
We tend to see, if we do have evidence of any butchering or killing, it's actually usually of things that have actually survived into the present. Things like, you know, the redneck wallaby or whatnot, which are quokkas, for example, that were consumed until recently. And so... It's quite interesting.
The Ancients
Ice Age Australia
There's, you know, the smoking gun of seeing, you know, these butchered sites with, you know, human artifacts and megafauna remains, remains to be seen or found. And I think that's really caused a lot of question about what the causal factors are to the extinction. And we've talked about some of the different animals.
The Ancients
Ice Age Australia
And I think, you know, a lot of what I do and what other researchers in the area are doing is, is trying to understand their paleoecology and paleobiology. So before we even get to sort of what killed them off, how did they live? And thinking about that, would they be vulnerable to these changes? And so Not to kind of go back a little bit, but to kind of feature one animal.
The Ancients
Ice Age Australia
So there's this one animal called Percoptodon goliath. And it's a short-faced kangaroo. Sorry, what was that? Percoptodon goliath. And it's a short-faced kangaroo, a goliath, right? It's a giant short-faced kangaroo.
The Ancients
Ice Age Australia
And interestingly, when people started studying this animal, it has a lot of morphological features or the shapes of its bones indicate that it was probably eating brows, which are things like leaves, in contrast to grass, which is pretty self-evident.
The Ancients
Ice Age Australia
And so when researchers started actually kind of looking at the isotopic signature, so this is a way to get at what the animal was actually eating. So a lot of the research that we do in our lab is, you know, you can use morphology or what you look like to infer diet. And that's one approximation. If people did an approximation of our diets, we would be omnivores. We are the classic omnivores.
The Ancients
Ice Age Australia
We have teeth that are ideal for, you know, crushing and grinding, we're not hyper carnivorous, we're not obligate herbivores, we're not just eating plants. Now, that being said, right, I might eat lots of sushi, and someone else might eat, you know, lots of steak, and someone else might be vegan. And Those are all, you know, variation.
The Ancients
Ice Age Australia
And you do have variation within natural populations as well, maybe not as extreme as human populations, but you do. And so we can use different tools. We can use the microscopic wear patterns on teeth. We can use the chemicals within the teeth themselves. to begin to piece together what those animals were doing when they were alive.
The Ancients
Ice Age Australia
Absolutely. And it still had a lot of the large effects that we faced across the globe. You know, the Ice Age phenomenon was really a global phenomenon, not a localized phenomenon.
The Ancients
Ice Age Australia
So morphology gives us that first approximation, but then we can actually drill their teeth and say, oh, this animal was eating a C4 plant or a C3 plant. And those are plants that photosynthesize a little bit differently. And then we can look at the microwear and say, oh, they were eating shrubs, not grass, or they were eating grass, not shrubs. And
The Ancients
Ice Age Australia
In Australia, things get really complicated really quickly because there's such a diversity of vegetation. And when I work in places like Florida or colleagues of mine who work in places like East Africa, it's a very simple system. You have essentially C4 grasses. So when you get a C4 signal, that means the animal's eating grass. And you have C3 plants.
The Ancients
Ice Age Australia
But in Australia, we have C3 grasses and C4 grasses. We have C3 shrubs and C4 shrubs. And so you can't really see anything unless you're both looking at the isotopes and looking at the microware. And you're probably at this point saying, well, why do I care if an animal was eating C4 shrubs or C3 grass or what that diet was?
The Ancients
Ice Age Australia
And it can tell us a lot about the environment, but it can also tell us about the vulnerability of that animal to that environment. So- In the case of Procter and Goliath, we end up finding that they are eating C4 shrubs. And this is based on both the microware and the isotopes. What that tells us is that they're consuming saltbush, right?
The Ancients
Ice Age Australia
They're consuming a lot of this species called, or this from the genus Atroplex. And as the name or the common name implies, saltbush has salts. And so if you're out hiking all day and you've got a bag of potato chips and you've got an apple in your bag, right? Which one are you going to go for if you haven't had water in the last few hours?
The Ancients
Ice Age Australia
Exactly. And so if you're going to consume this resource, which is prevalent in large parts of Australia, that's great. That's a resource that these animals can exploit, it's a niche that they can sort of occupy, but it also requires that they are consuming water. And we actually also see that in their oxygen isotopes.
The Ancients
Ice Age Australia
As you are what you eat and everything is incorporated into your tissues, everything you drink is also incorporated into your tissues. And so we can actually see that for optongoli compared to other co-occurring kangaroos has much lower oxygen isotope values, indicating that it's drinking water. It's not just getting water from plants that it's eating.
The Ancients
Ice Age Australia
So the entire Pleistocene, which is the last 2.6 million years, is really defined as occurring during periods of glacial interglacial period. So you have these sort of cycles from full glacials where you have extensive ice sheets in different regions of the world, much lower sea levels. And so all of these things affects the entire globe.
The Ancients
Ice Age Australia
So what this tells us is you have this giant... C4 browser that's eating saltbush predominantly on the landscape. It's going to require water, and it's going to require water at regular intervals. As the environment starts to dry out and you have increased aridification, it's going to make this animal more vulnerable to extinction.
The Ancients
Ice Age Australia
The fact that this animal is also large makes it more vulnerable to extinction because what we know about larger animals is they typically produce fewer offspring. And so anything that is smaller in number and occupies more space is more likely the possibility of getting to zero through various stochastic or random processes is more likely the smaller that number is.
The Ancients
Ice Age Australia
So these are all things that make it vulnerable. Also, if it's going to watering holes, it's more vulnerable to predation. And that predation could be humans. It could be humans predating on them, although we don't have any direct evidence of that. But equally likely is it could be, you know, giant chompy things, right? Crocodiles.
The Ancients
Ice Age Australia
You see that as things are getting water at watering holes, whether that's in Africa or in Australia, crocodiles are more than happy to take advantage of the naive or the less observant prey animal that comes up to the water and doesn't see that the crocodile's there.
The Ancients
Ice Age Australia
Yes, absolutely. And so it makes Rehobotan Goliath incredibly vulnerable if water sources are becoming fewer and far between, or if the risk at these water sources is increasing in any way. And so what do we see? We see them go extinct. And this gives us Cause about what those drivers may be.
The Ancients
Ice Age Australia
You know, we don't have any evidence that of humans hunting them, but we do have pretty clear evidence that their ecological niche would make them vulnerable to a reduction in water on the continent.
The Ancients
Ice Age Australia
Yeah, so all things being equal, larger things are more vulnerable to extinction, at least in the present day. And we know this by studying modern animals. Animals have different ways in which they can reproduce and invest their energy, and there's constantly trade-offs. So you can either invest your energy in getting really big and also making sure your offspring have lots of resources.
The Ancients
Ice Age Australia
Or you can have lots of offspring, but the chance of any one of those surviving is going to be lower. So some classic examples of this are if you think of, you know, fish, right? So fish have tons and tons of eggs. What's the chance that, you know, any one of them is going to survive is pretty low, but they have so many that it's sort of a numbers game, right? Inevitably, likely some will survive.
The Ancients
Ice Age Australia
So when you remove that water from the ocean, place it into glaciers, essentially, it's you're then lowering the sea level to a significant level. So at the time that Australia was experiencing full glacial periods, you could literally walk from Papua New Guinea across to Australia, across to Tasmania,
The Ancients
Ice Age Australia
Alternatively, you have things on the far end of the spectrum, things like elephants, right? They have a long gestation period. They produce one offspring, much like us, during each cycle of reproduction. And they invest heavily in that one offspring. There's a lot of investment, both in the amount of time it's in that gestation period.
The Ancients
Ice Age Australia
So a lot of time and resources before it's born, but there's also a lot of time and resources and parental care after it's born. And humans are, you know, obviously one of the most extreme, right? We invest quite a lot, right? Our kids are with us for, you know, 18 years. That's a long time. And, you know, we're investing in them before they sort of go off.
The Ancients
Ice Age Australia
But even so, even if it was even at a slightly younger age, there's still a lot of parental care that's being invested. And so when you have things that can reproduce quickly. Things like rodents, rabbits, they produce lots of offspring at one time. Some of them can reproduce multiple times a year. Those things are able to sort of respond.
The Ancients
Ice Age Australia
It's sort of a numbers game to any stochastic processes, right? Some of them might go extinct as well. But likely some of them are going to survive.
The Ancients
Ice Age Australia
But if you have these really large animals and you have a variety of forces that are perturbing them, and those can be climate change, they can also be human-caused forces like overhunting or habitat fragmentation, automobile accidents, all sorts of things, that's going to lower those numbers significantly. And the closer you get down to zero, if you hit zero, that's it.
The Ancients
Ice Age Australia
If you even hit one, that's it, right? And so you can't reproduce and you can never recover from that. So it's really a numbers game. And unfortunately, the things that are the biggest in many cases, today at least, are the things that are most vulnerable to going extinct.
The Ancients
Ice Age Australia
Yeah, so the idea used to be, and I'm going to kind of give you a little bit of the history because it explains, it gets into the extinction debate a little bit. But the idea used to be that they thought people came over roughly about 45,000 years ago. And they also thought that a lot of the megafauna were going extinct around this time.
The Ancients
Ice Age Australia
And so there was this sort of reigning hypothesis called the Blitzkrieg Hypothesis. And this was not only suggesting humans as the causal agent for extinction of these megafauna, but it was suggesting that it happened in a very, very rapid period of time, a thousand years, potentially. Now, we learned a lot since then.
The Ancients
Ice Age Australia
And one of the things that we've learned is actually people came over much earlier. And so now the estimates are closer to about 65,000 years. And that's based on archaeological evidence found in the northern part of Australia and other sites that also show megafauna. We have some sites that show coexistence of humans and megafauna, which is really exciting.
The Ancients
Ice Age Australia
That was considered one large lamb mass because the continental shelf was exposed and the sea level was lower. Animals and people could walk back and forth as needed.
The Ancients
Ice Age Australia
So there's a site called Lake Mongo and also a site that I worked quite extensively with, which is called Cuddy Springs.
The Ancients
Ice Age Australia
Yes. And Cuddy Springs is an inch. So when I first my first trip to Australia, you know, I went over there really interested in looking at sort of extreme responses to climate change. And I had no idea that, you know, Cuddy Springs at the time was as controversial as it was. And one of the reasons it was so controversial, and I say was because we've learned a lot since
The Ancients
Ice Age Australia
is that it was one of the few sites at the time that actually showed coexistence of humans and megafauna to about, you know, 30,000 years ago. And this idea, just the existence of Cuddy Springs showing coexistence of megafauna at some time after this 40, 45,000 year interval went against this Blitzkrieg hypothesis. And so it received a lot of what I think is, is, probably unfair scrutiny.
The Ancients
Ice Age Australia
Any site needs scrutiny. But it was sort of not a rigorous scientific debate. It was more of a reigning hypothesis and, you know, not well-tested debate where people were kind of going back and forth, just trying to knock Cuddy Springs out of the picture, essentially. And they would say, oh, well, it's a mixed assemblage. And the woman who has done so much for the site is Jude Field.
The Ancients
Ice Age Australia
She's an archaeologist. She excavated the site for decades and worked with First Nations people to learn about the history of the site and to excavate it with them as well and really did a lot of remarkable work. But, you know, anytime there was sort of a contentious issue... She would go out and find the best person to help sort of test that question.
The Ancients
Ice Age Australia
And so, for example, when they said, oh, it's a mixed assemblage, everything's jumbled together. Well, let's test that. So she reaches out to Clive Truman, who's an expert on rare earths. And they used rare earths, which is a kind of a way of looking at different chemical signatures. And in fact shows, no, we have these sort of intact assemblages.
The Ancients
Ice Age Australia
And just for a long time, I think just Cuddy Springs being Cuddy Springs. And I'm sure there was, you know, the fact that you had a female archaeologist leading a lot of this work and contrasting what a lot of the archaeologists typically male archaeologists were saying at the time. I'm sure that played into it as well, but it was really contentious.
The Ancients
Ice Age Australia
And when I started working on the site, I was really interested, not so much in the extinction, but what were these animals doing? What is a diprotodon eating? What are these different kangaroos eating? what are, you know, we have these ideas based on their morphology, but what is their diet? And what can we tell about these animals?
The Ancients
Ice Age Australia
Yes. Although again, it's fluctuating, right? So there's going to be periods where you have an interglacial and you can't, you have to, you know, use some other means or those, those pathways are cut off or whatever species that might be and other periods where they're connected.
The Ancients
Ice Age Australia
So when I went over there, I was really interested in looking at the change from, so there's one particular horizon of the site that's roughly dated to around 400,000 years. So this is far before people arrived, right? This is the Ice Age Australia, megafauna raining over the continent, not a human in sight. But then there's another layer that's much more recent, around 30,000 years.
The Ancients
Ice Age Australia
And so what we did is we actually looked at all of the animals that were in both of those different horizons and had been carefully excavated. And I will say, being a paleontologist and knowing archaeologists, archaeologists do a far better job of excavating fossil localities. Paleontologists, we're so excited to get it fixed up. Archaeologists meticulously will map out the site.
The Ancients
Ice Age Australia
And this often is now occurring in And paleontological sites, but still not to the rigor and the level that archaeologists do it. But everything had been meticulously excavated. And so we knew the horizons that they were in, that rare earths had been done.
The Ancients
Ice Age Australia
And when we looked at the isotopes, what we found was pretty astounding is that the kangaroos, we know kangaroos are actually really good at telling us something about climate. And we know that based on modern kangaroos today. So you can look at kangaroos from really wet environments, really dry environments, and sort of in between.
The Ancients
Ice Age Australia
And you can actually use those oxygen isotopes to reconstruct the environment. And we can do that with modern ones. So we know where these kangaroos are from. We know that they live in high rainfall areas or low rainfall areas. We look at the oxygen isotopes and we see this beautiful map where we can say, okay, these are from drier areas, these are from wetter areas.
The Ancients
Ice Age Australia
And once we sort of have tested that to make sure it works in the modern, we can take that back into the fossil record. And so when we do that at Cuddy Springs, we see that you're going from a fairly dry environment, but to a drier environment.
The Ancients
Ice Age Australia
So you basically fluctuate from about two and a half million years ago to near the present, going from sort of glacial interglacials and these cycles of being connected, isolated, connected, isolated.
The Ancients
Ice Age Australia
Yes, absolutely. So as you're kind of comparing the different layers, we can see this sort of shift in the oxygen isotope. So it's not going from wet to dry. You're going from dry to drier. And with that, we can also look at what the animals are eating. So the oxygen tells us about what the water is like or what the climate is like.
The Ancients
Ice Age Australia
And the carbon isotopes can tell us what exactly they were eating. Were they eating C3 plants or C4 plants? And then we can look at the microware, which can tell us was it shrubs, was it grass? And so when we begin to map this out, What we find is that with increased aridification, so as things are getting drier, which we can see with the kangaroos, right?
The Ancients
Ice Age Australia
So the kangaroos are also demonstrating this at the site. We also see a shift away from eating C4 resources. And this is actually in contrast to what I see in Florida happening during glacial and interglacial time. So when you go from sort of a forested ecosystem to this C4-C3 mixed ecosystem where you have C4 grasses and C3 shrubs in Florida during the Pleistocene, it's great.
The Ancients
Ice Age Australia
You've got horses and animals. mammoths and all sorts of things that are able to eat the C4 resources. You have other things that are browsing. You actually have like two different types of camels that exist because one can do one thing and one can do the other. And so it's sort of, you know, this more resources in the landscape.
The Ancients
Ice Age Australia
What's interesting about Australia is that these animals stop eating these C4 resources. And this got us thinking, okay, well, what are these C4 resources? Well, it turns out, similar to Procopta and Goliath, the short-faced kangaroo, many of these C4 resources are things like saltbush. And so we don't know if the saltbush has gone away. In fact, we don't think it has.
The Ancients
Ice Age Australia
We think it's probably stayed on the landscape. But what we do are learning is that these animals are likely unable to eat those resources, eat that C4 saltbush anymore. So they're having to sort of not eat that food and now having to compete for more similar resources. So with the drying out of the continent that's happening sort of globally, but also locally, the Lake Erie Basin is drying out.
The Ancients
Ice Age Australia
You have the weakening of the monsoon signal, for example. You're seeing this shift in the kangaroos that's being recorded via climate, but you're also seeing sort of a dietary shift away from certain resources. And so aside from everything, I think what it's telling us is that animals are vulnerable to changes in the climate, that we do need to consider what the impacts are of a ratification.
The Ancients
Ice Age Australia
And the funny thing is, whenever I talk about this, whenever I give seminars and I show these data, I sort of, you know, I look at the room and the room sort of like, yeah, okay, well, what new thing are you telling us? Like, this doesn't seem earth shattering or groundbreaking. You know, the animals are vulnerable to climate change.
The Ancients
Ice Age Australia
I said, yeah, but when we published that paper, the paper took us a while to get out. We want to make sure it was done right. I was also... I went transitioning from a grad student to a junior faculty setting at my lab, getting the machinery and equipment to be able to properly, you know, ask and answer the questions.
The Ancients
Ice Age Australia
But when that paper came out, about a week prior, the paper came out that said, so January of 2017, January 20th of 2017, papers from Nature Communications said, humans rather than climate, the primary cause of Pleistocene megafaunal extinctions in Australia.
The Ancients
Ice Age Australia
And then our paper came out about a week later and said, didn't say anything about causal factors, but said dietary responses of Sahul, licensing Australia, New Guinea, megafauna to climate environmental change and talked about those impacts.
The Ancients
Ice Age Australia
Sure. Yeah, they're pretty standard and largely caused by sort of orbital cycling. And so the Milankovitch cycles contribute to the magnitude at which they occur and also the regularity at which they occur. And typically, you have sort of these fluctuations, you have different sort of clocks moving and different sort of patterns that are actually happening. So
The Ancients
Ice Age Australia
What was interesting is that within a few weeks of our paper coming out, another paper came out in February 2017 saying at least 17,000 years of coexistence between modern humans and megafauna. And this is from the Lake Mungo Willandra Lakes site that was led in the paper that was led by Michael Westaway.
The Ancients
Ice Age Australia
But essentially, they demonstrated another site that showed an animal called Zygomaturis and megafauna coexisting for some period of time. So now it's not just Cuddy Springs that's showing this, that people were sort of so eager to just kind of throw out to fit their theory. You now have an additional site that's showing prolonged coexistence.
The Ancients
Ice Age Australia
And then later that year, July 20th of 2017, a paper came out in Nature saying human occupation of northern Australia by 65,000 years ago. And so we're starting to see this sort of more complete picture of coexistence. of what's sort of happening, in which case there might be, you know, more prolonged coexistence of humans, a variety of causal factors.
The Ancients
Ice Age Australia
But I think it just goes to show the importance of actually kind of stepping back and trying to understand just even the paleobiology of these animals, what they're doing before we jump on any one theory and to try to argue, you know, why these were going extinct.
The Ancients
Ice Age Australia
Yes. Yeah. It's related to diprotodon. It's maybe more of a forested dweller or some different hypotheses there. But yes, it's a maybe think of a smaller rhino size or a large taper size, but still quite large.
The Ancients
Ice Age Australia
Yeah, I think that's a great question. I think what we really have to do is look at the evidence. I am a scientist. I look at data and I try not to. I'm sure I have my own biases, but I try to be open minded when new data come about. So, for example, and I'm going to transition to a different continent in North America.
The Ancients
Ice Age Australia
I was part of a team that did a very large study that came out in science in 2023 about the megafaunal extinction, the timing of it at La Brea. And there, the data look as if The megafauna, at La Brea at least, are going extinct locally right about the same time when fire frequency is skyrocketing. And I mean skyrocketing. It's going from minimal amounts of charcoal to... huge spike.
The Ancients
Ice Age Australia
They tend to be fairly regular over the long term, but they can be variable. But you typically go from a period of pronounced glacials and then you start having, you know, the warming, the melting of the ice that's going to cause sort of a...
The Ancients
Ice Age Australia
I don't know how better to explain it. It's literally just jumping in magnitude. And so there, we don't know. We don't know, was it humans who were lighting these fires? Presumably, this is at the same time when humans are increasing their prevalence in these areas. We do know that they used fire. But it's something that you can't ignore, right?
The Ancients
Ice Age Australia
The humans very well may have played a large role in altering the ecosystems in North America. But when I look at Australia, There haven't been any sites that have demonstrated conclusively that these large megafauna were hunted or consumed. That is compelling. And so there's no clear evidence. There's only a few sites that show coexistence. And it is possible, of course.
The Ancients
Ice Age Australia
But I think what's happening is the reigning hypothesis for so long has been one of humans coming onto the continent, you know, killing off everything very quickly. And then iterations of that hypothesis just keep getting, you know, stretched thinner and thinner and thinner. And I think it's important if we look at all the factors. And so my students will often ask me, like, why does it matter?
The Ancients
Ice Age Australia
Why does it matter if it's climate change or if it's humans that are contributing to the extinction? And this is what I tell them. Presumably, if it is just humans, if human overhunting was the cause of these megafaunal extinctions, then if we stop hunting these animals, then presumably, everything will be fine, right?
The Ancients
Ice Age Australia
That these animals would be able to respond positively and you remove that factor. But if climate change played any role, whether that was a synergistic role, whether that was the primary role, whether that was a secondary role, We are now living in a world in which human impacts and climate change are linked and occurring in concert together.
The Ancients
Ice Age Australia
And so if climate change did play a role in the past, that's really important to know and to be able to learn and disentangle, especially if we need to sort of think about that and how we would manage for ecosystems moving forward.
The Ancients
Ice Age Australia
the warming in general of other surrounding areas, you have these positive feedback loops that basically lead to expedited warming events, which usually happen pretty quickly. And then again, sort of, you'll start to have cooling events that will happen there on after. So you just kind of go from cycle to cycle between glacial and interglacials.
The Ancients
Ice Age Australia
And the more and more I, you know, I investigate these different animals, whether it's the, you know, giant turf-faced kangaroo that was eating C4 shrubs and eating saltbush and requiring water, or the one I didn't really get to talk about much yet is the marsupial lion that we think was actually hunting, you know, just from things from forests.
The Ancients
Ice Age Australia
And so we know that based on the isotopes, and we've looked at the They have, you know, bolt cutters for teeth. They could eat whatever they wanted, but they are only eating things actually within these dense forests. And so what that tells me is that when environments are getting drier and opening up and fewer forests,
The Ancients
Ice Age Australia
that these animals are losing the upper hand that they have, which is being able to ambush hunt from trees potentially, or eating these forest browsers. These forest browsers are also disappearing from these ecosystems. And so in the case of the marsupial lion or killer wombat, whatever you want to call it, it's no match for climate change.
The Ancients
Ice Age Australia
And so I think we have to just, I think we have to remain open And, you know, continue to evaluate all the different hypotheses. And to, you know, on that note, I remain open about looking at the impacts of humans. I just don't want to prematurely assume it was humans when we don't necessarily have clear evidence that it was. And I also think it's important. So I'm not an archaeologist.
The Ancients
Ice Age Australia
I think I should I should make that clear. I'm a paleontologist. But in Australia, a lot of the sites are, you know, most of the sites are paleontological and a few have archaeological remains. But paleontologists and archaeologists work together all the time.
The Ancients
Ice Age Australia
But it may be it's a bit different than, say, some of the other guests you've had on for other shows where the archaeologists are kind of working within a much more recent time frame. But one of the things I was just going to mention is that the First Nations people today, at least, have a very different concept of sort of wildlife management than we do. And it's this concept of country.
The Ancients
Ice Age Australia
And, you know, as opposed to a much more sort of Western view of humans on the top of the food chain and everything else below, this concept of country includes humans as one of the many different biological entities on the planet, no more or less than anything else.
The Ancients
Ice Age Australia
A few of the things that I've become aware of or learned about are things like totems and how different individuals within different groups would be, you know, sort of assigned a totem or an animal that they were responsible for. And this was an animal that they would not consume, but it was an animal that they also would try to manage, right?
The Ancients
Ice Age Australia
And they would be knowledgeable about if the population was increasing or decreasing and And so, you know, I think there's a lot more work and I think we, I am excited to engage in more work with First Nations people. I think there's a lot more work that is being done actively by archaeologists in this area, also by paleontologists.
The Ancients
Ice Age Australia
But there's, there's a lot that I think I, you know, we don't fully understand with sort of how people were managing or respecting their environment. And also we need to kind of consider those factors. We can't just take the sort of Western view of conquering, bring it to Australia and say, therefore megafauna went extinct.
The Ancients
Ice Age Australia
We need to kind of step back, really evaluate and be open to other hypotheses. Of course.
The Ancients
Ice Age Australia
Sure. So our lab is the DREAM Lab, which stands for Dietary Reconstructions and Ecological Assessments of Mammals, which is a bit of a mouthful. But what we're trying to do is really understand how mammals have responded to climate change in the past. And there's actually an entirely new field that sort of developed within the past few decades, which is referred to as conservation paleobiology.
The Ancients
Ice Age Australia
So much like conservation biology, we ask questions that are of relevance to conservationists, but we actually use the fossil record to ask and answer those questions. So we try to look at which animals responded to these climate changes or what were the impacts of these extinctions.
The Ancients
Ice Age Australia
And a lot of the questions that we've been trying to look at is not just why did animals go extinct, but what were the subsequent consequences of those extinctions on other animals or on those ecosystems? And so I study mammals broadly. I love working in Australia. I love sort of studying them, experiencing some of the most arid conditions.
The Ancients
Ice Age Australia
Yes, Sahul. I don't know the exact pronunciation, but that's how I say it with my American accent.
The Ancients
Ice Age Australia
This provides us essentially like a canary in the coal mine of what we might expect in the western part of North America, for example, experiencing all these fires. This is very similar to what happens in Australia as well in these different sort of Mediterranean climates. So in some ways, we're trying to use what we can from the past to
The Ancients
Ice Age Australia
to extract important sort of conservation lessons and even cautionary lessons that can be of relevance to today. And so, you know, I have the privilege of being able to do this on most continents. I primarily work in North America and in Australia, although I have colleagues and collaborations on all continents except for Antarctica.
The Ancients
Ice Age Australia
The dating of a lot of these sites can be fairly challenging. A lot of what we have is identified to Pleistocene. And so we don't exactly know from some localities when exactly those animals are occurring in time. Other sites, we have a bit more precision.
The Ancients
Ice Age Australia
The challenge with a lot of the specimens is that, you know, at the times of megafauna and what might be sort of the heyday in other places like North America, you have lots of megafauna at places like the La Brea Tar Pits and you have a really good record for the past 50,000 years. That's well within the time that we can actually radiocarbon date specimens.
The Ancients
Ice Age Australia
A lot of the specimens that you're getting from Australia, some don't preserve the collagen, which allows for the radiocarbon dating. Others are sort of beyond the limits of radiocarbon dating. So they're older than 50,000 years. So other forms of dating are used to try to date sort of the sediments surrounding these fossils.
The Ancients
Ice Age Australia
But I'd say a lot of the material that we know the most about is from the latest Pleistocene. So somewhere around, you know, 60,000 to 30,000-ish years. And there's a variety of sites. Now, there's also a lot of material that we've identified to Pleistocene. It could well fall in that area. It might be much older. And so it's hard to know exactly.
The Ancients
Ice Age Australia
So what essentially happens is with any sort of radiometric dating, you have a parent product and then what they call the daughter product. And essentially what happens is you have decay from that parent product to this daughter product and you measure the ratio between these. And the half-life for C14 is somewhere around 5,000 years.
The Ancients
Ice Age Australia
And so after 5,000 years, half of that product has been converted or has undergone decay. And so at the point that you're getting towards that 50,000 window, you have such small amount of material and it's approaching sort of limits of the machinery, the technology to be able to measure it. And then there's no more.
The Ancients
Ice Age Australia
And so essentially, when we're doing any carbon dating, we are fundamentally limited to the last roughly about 50,000 years. 40,000 is probably where we get good dates. Other places in the world, we can get really nice chronologies leading up to sort of extinction events. But in Australia, it's a bit more challenging. And so other methods are used.
The Ancients
Ice Age Australia
The other, you know, a lot of times when you hear about radiometric dating during the time of the dinosaurs, that's using volcanic ash layers. So you have these volcanic events and you're using a different, you're usually looking at potassium argon dating or a different metric. And so different amounts of decay that's happening at different rates.
The Ancients
Ice Age Australia
That's giving us some sort of indicator of what time those events are happening. But again, that precision, those tools are a lot harder to use in Australia. We don't have a lot of the volcanic ash layer in events, especially in the late Pleistocene.
The Ancients
Ice Age Australia
Sure. There was all sorts of amazing animals. One of my favorite illustrations is actually one that was commissioned by the Australian Postal Service. It ended up making a series of stamps. On that image, you get to see some of the classic ones. You get to see diprotodons, which are giant wombat-like animals the size of rhinos.
The Ancients
Ice Age Australia
Yes, or wombat-like animals. They're not quite wombats, exactly. But they were massive. We don't think of large megafauna of that scale in places like Australia today. You also had giant kangaroos. And when I mean giant, I mean giants. Taller than the average person, several meters in height. You would be looking eye to eye or actually looking up at them in many cases.
The Ancients
Ice Age Australia
We also had things like giant goannas. So if you think of the goannas that you might see in Australia today, imagine them the size of a saltwater crocodile.
The Ancients
Ice Age Australia
Yes. So that's, I feel like, not as hard to envision in Australia because we have giant flightless birds there today, right? So it's still home to cassowaries and emus. But at the time, there was other giant birds that were sort of, might have resembled more of like a duck shape, a geniornis, much more massive.
The Ancients
Ice Age Australia
So think of like a heavyweight emu, for example, maybe several times its mass, but about the same size. As well. And so, you know, yes, just a menagerie of really interesting things. And I haven't even mentioned what I think is the coolest, the most interesting and most exciting. One of my favorites is actually often referred to as the marsupial lion.
The Ancients
Ice Age Australia
But I have a colleague who actually refers to it from a much cooler name. And that name is a killer wombat.
The Ancients
Ice Age Australia
A killer wombat. And it's not totally an unfounded name. So very similar to how, you know, giant pandas are an herbivorous animal that eats plants that evolved from a carnivorous group, right? They're a bear. They're related to grizzly bears and black bears and polar bears, things that primarily eat meat or are more omnivorous.
The Ancients
Ice Age Australia
Much like that, we have sort of the reverse, where you have this killer wombat or this marsupial lion, this carnivorous animal that evolved from an herbivorous group of animals and became sort of the largest mammalian predator in Australia. And it's always kind of funny because, you know, the Australians like to scare the tourists and talk about these things called drop bears.
The Ancients
Ice Age Australia
Yes, yes, yes. But these were sort of like, you know, ancient drop bears in a sense. We think that they hunted primarily from trees. Based on their morphology, they look like much more bear-like or ambush predators. They weren't cheetah-like at all. They weren't chasing things in like open ecosystems. They were definitely, you know, using the element of surprise to take down any prey.
The Ancients
Ice Age Australia
And in fact, a lot of the work we've done, and I'm happy to elaborate on it, really suggests that they work committed to forested ecosystems, that they were in fact hunting from these trees. They were only eating things that were consuming vegetation in the densest of the forests. And so they relied on these trees to do their hunting. And in fact,
The Ancients
Ice Age Australia
What we're sort of learning about them, and I can go into sort of how we've learned this, but what we're learning about them is that these top mammalian predators were really no match for climate change in this particular scenario because you have the opening up of these landscapes, aridification that's happening, declines in forests, and these animals were finding out
The Ancients
Ice Age Australia
Although they could, you know, crunch or eat a variety of different things, they were highly specialized on things that were browsing or eating leaves in forested environments.
The Ancients
Ice Age Australia
Yeah, so there were some differences, right? There are some areas that actually today are named, you know, Nilabor, which means no tree. But there's evidence of animals living there that would have required forested ecosystems. So what we do know is that they likely experience fairly extreme environmental fluctuations, right? So going from, you know,
The Ancients
Ice Age Australia
really wet periods, intense monsoons to really dry periods. And what we do know is that the monsoon, the strength of the monsoon is sort of weakened over time. And this has led to widespread aridification or the drying out of the continent. And I think often people sort of underestimate the role that extreme heat and drought can play on an ecosystem.
The Ancients
Ice Age Australia
But it's definitely, you know, having an effect and may be sort of like a thresholding effect, right, where there's certain animals that just can't live in environments that are too hot or too dry. And that's largely affecting kind of their distribution today. At the time, you know, a lot of things were bigger, right?
The Ancients
Ice Age Australia
So you had, you know, we talked about the diprotodon, the giant wombat-like animal the size of a rhino, but you had several different types of those. You had another one called zygomaturis, and you had another one that was sort of like a tapir a little bit, although maybe it was more like a sloth is now we're learning. And so you had lots of these large animals.