Ice Age Australia

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Speaker 1 The woolly mammoth, the saber-toothed tiger, the giant ground sloth.

Speaker 1 When someone mentions the ice age, you might immediately think of great beasts like these, these large animals that roamed the Pleistocene landscape and are today extinct.

Speaker 1 But what about the Procopteron Goliah, a giant short-faced kangaroo?

Speaker 3 Or the Diprotodon, a massive herbivorous marsupial also known as the killer wompat?

Speaker 1 Or perhaps the Wanambi, a huge species of snake similar to modern-day pythons. These frightening lesser-known megafauna that lived on the supercontinent that was Ice Age Australia.

Speaker 1 It's the ancients on History Hit. I'm Tristan Hughes, your host.
Today we're exploring the extraordinary world of Ice Age Australia.

Speaker 1 We'll explore the climate, the many different individual beasts that once roamed the land, the arrival of humans around 60,000 years ago, and why many of these megafauna ultimately went extinct.

Speaker 1 Our guest today is Professor Larissa DeSantis from Vanderbilt University.

Speaker 1 Larissa is a paleontologist who has been studying the megafauna of Ice Age Australia, looking at the fossil record, including those from a remarkable site in New South Wales called Cuddy Springs.

Speaker 1 Larissa has examined how climate change may well have contributed to the extinction of these giant kangaroos, killer wombats, flightless birds, and so on.

Speaker 1 She's here to give us an introduction to the amazing world of Ice Age Australia and why its story deserves to be better known.

Speaker 1 Larissa, it is such a pleasure to have you on the podcast today.

Speaker 3 Thanks so much for having me.

Speaker 1 What an intriguing topic. Ice Age Australia.
When I first think of the Ice Age, I will think of Europe or North America of woolly mammoths.

Speaker 1 Don't instinctively think of Australia, but this was a place that had a great variety of these extraordinary, quite unique megafauna.

Speaker 3 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.

Speaker 1 And is it just Australia at the time of the ice age, or should we be thinking bigger?

Speaker 3 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.

Speaker 3 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.

Speaker 3 So when you remove that water from the ocean, place it into glaciers essentially, you're then lowering the sea level to a significant level.

Speaker 3 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.

Speaker 3 And so all of that was considered one large sort of landmass because the continental shelf was exposed and all of those areas were were much, the sea level was lower.

Speaker 3 And so animals could literally, and people could walk back and forth as needed.

Speaker 1 It's a huge area. So we should be imagining those land bridges between those areas of sea that we think of today.

Speaker 3 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.

Speaker 3 you know, use some other means or those pathways are cut off for whatever species that might be. And other periods where they're connected.

Speaker 3 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.

Speaker 1 And the duration, the longevity of those glacial and interglacial periods, do they, I mean, is there variety? Are they quite different in length or is there quite a standard length between the two?

Speaker 3 Sure. Yeah, they're pretty standard and largely caused by sort of orbital cycling.

Speaker 3 And so the Milenkovich cycles contribute contribute to the magnitude at which they occur and also the regularity at which they occur. And typically you have sort of these fluctuations.

Speaker 3 You have different sort of clocks moving and different sort of patterns that are actually happening. So they tend to be fairly regular over the long term, but they can be variable.

Speaker 3 But you typically go from a period of pronounced glacials and then you start having, you know, the warming.

Speaker 3 the melting of the ice that's going to cause sort of the warming in general of other surrounding areas.

Speaker 3 You have these positive feedback loops that basically lead to expedited warming events, which usually happen pretty quickly.

Speaker 3 And then again, sort of, you'll start to have cooling events that will happen thereon after. So you just kind of go from cycle to cycle between glacial and interglacials.

Speaker 1 And the periods when you do have that large landmass stretching from the Philippines to Tasmania Orissa, I've got in my notes the name Sahul. Is that the name it's given?

Speaker 3 Yes, Sahul, or I don't know the exact pronunciation, but that's how I say it with my American accent.

Speaker 1 And as we're going to be talking and focusing in on quite a few examples of these Ice Age megafauna from that great continent, in those 2.6 million years, is there a particular heyday for the Ice Age and these Ice Age megafauna that we can focus in on?

Speaker 3 The dating of a lot of these sites can be fairly challenging.

Speaker 3 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.

Speaker 3 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 Labrea 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.

Speaker 3 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.

Speaker 3 So they're, you know, older than 50,000 years. So other forms of dating are used to try to date sort of the sediments surrounding these fossils.

Speaker 3 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.

Speaker 3 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.

Speaker 1 Now, you mentioned also in that explanation, Larissa, radiocarbon dating. So this is

Speaker 1 a particular type of dating fossils and so on, but for evidence older than 50,000 years, is the carbon not there so you can't date it as accurately? Is that what radiocarbon dating is?

Speaker 3 So what essentially happens is with any sort of radiometric dating, you have a parent product and then what they call the daughter product.

Speaker 3 And essentially what happens is you have decay from that parent product to this daughter product and you measure the ratio between these.

Speaker 3 And the half-life for C14 is somewhere around 5,000 years. And so after 5,000 years, half of that product has been converted or has, you know, undergone decay.

Speaker 3 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.

Speaker 3 And then there's no more. And so essentially,

Speaker 3 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.

Speaker 3 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.

Speaker 3 The other, you know, a lot of times when you hear about free metric dating, you know, during the time of the dinosaurs, that's using volcanic ash layers.

Speaker 3 So you have these volcanic events and you're you're using a different, you're usually looking at potassium argon dating or a different metric.

Speaker 3 And so different amounts of decay that's happening at different rates. And that's giving us some sort of indicator of what time those events are happening.

Speaker 3 But again, that precision, those tools are a lot harder to use in Australia. And we don't have, you know, a lot of the volcanic ash layer and events, especially in the late Pleistocene.

Speaker 1 Well, it's very commendable for yourself and others in the field then who are analyzing sediments or whatever for those sites which are older than 50,000 years ago.

Speaker 1 And I'm guessing it's looking at sediments from there and other evidence surviving Larissa to get more of an understanding of the great amount and variety of megafauna that existed in Australia for much of the Ice Age.

Speaker 1 And I've got lots of different things on my sheet in front of me, lots of different animals that hopefully we can get through.

Speaker 1 But can you give us an idea of what types of great beasts of megafauna existed in Ice Age Australia?

Speaker 3 Sure. There was all sorts of amazing animals.
One of my favorite illustrations is actually one done that was commissioned by the Australian Postal Service, and it ended up making a series of stamps.

Speaker 3 And 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.

Speaker 1 Giant rhino-sized wombats.

Speaker 3 Wow. 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.

Speaker 3 You also had giant kangaroos. And when I mean giant, I mean giant, taller than the average person, you know, several meters in height.

Speaker 3 You would be looking eye to eye or actually looking up at them in many cases. We also had things like giant goannas.

Speaker 3 So if you think of, you know, sort of the guanas that you might see in Australia today, imagine them the size of a saltwater crocodile.

Speaker 1 Flightless birds as well? I mean, a terror bird or a massive dodo equivalent, were there?

Speaker 3 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.

Speaker 3 But at the time, there was other giant birds that were sort of might have resembled more of like a duck shape, a geniornice, much more massive.

Speaker 3 So think of a very 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.

Speaker 3 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.

Speaker 3 But I have a colleague who actually refers to it from a much cooler name. And that name is a killer wombat.

Speaker 1 A killer wombat. Amazing.

Speaker 3 A killer wombat. And it's it's not totally an unfounded name.
So very similar to how,

Speaker 3 you know, giant pandas are an herbivorous animal that eats plants that evolved from a carnivorous group, right? It's they're a bear.

Speaker 3 They're related to grizzly bears and black bears and polar bears, things that primarily eat meat or are more omnivorous.

Speaker 3 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.

Speaker 3 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.

Speaker 3 I don't know if you've ever heard of this. Oh, yes.

Speaker 1 I was in Australia for a year or so. I heard the drop bear stories.

Speaker 3 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.

Speaker 3 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...

Speaker 3 you know, using the element of surprise to take down any prey.

Speaker 3 And in fact, a lot of the work we've done, and I'm happy to elaborate on it, really suggests that they were committed to forested ecosystems, that they were in fact hunting from these trees.

Speaker 3 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,

Speaker 3 what we're sort of learning about them, and I can go into sort of the

Speaker 3 how we've learned this, but what we're learning about them is that, you know, 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, 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.

Speaker 1 I mean, Larissa, you mentioned your work around climate change. We're going to get to that, especially when we get to that question around extinction and also with the arrival of humans.

Speaker 1 We're going to get to that as this chat progresses.

Speaker 1 But keeping on climate, but not so much climate change, when you have these, you know, these killer wombats, these great birds, these lizards, these giant kangaroos, and so on, you know, numerous species.

Speaker 1 The environment that they were best suited to, I mean, do we know much about the climate, the environment in Ice Age Australia?

Speaker 1 I mean, Australia today, you have, of course, you've got the bush, but you've also got the outback and you've got nicer areas as well. Was it just as diverse back then? What do we know?

Speaker 3 Yeah, so there were some differences, right?

Speaker 3 There are some areas that actually today are named, you know, nilabore, which means no tree, but there's evidence of animals living there that would have required forested ecosystem.

Speaker 3 So what we do know is that they likely experience fairly extreme environmental fluctuations, right? So going from, you know,

Speaker 3 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.

Speaker 3 And this has led to widespread aridification or the drying out of the continent.

Speaker 3 I think often people sort of underestimate the role that

Speaker 3 extreme heat and drought can play on an ecosystem, but it's definitely having an effect and may be sort of like a thresholding effect, right?

Speaker 3 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,

Speaker 3 a lot of things were bigger, right? So you had,

Speaker 3 we talked about the

Speaker 3 antiprotodon, the giant wombat-like animal the size of a rhino, but you had several different types of those.

Speaker 3 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.

Speaker 3 And so you had lots of these large animals.

Speaker 3 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

Speaker 3 a type of vegetation that's difficult to eat today. primarily because it has lots of salt.
So salt bush is, you know, has salt and and requires you drinking a lot of water.

Speaker 3 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 today.

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Speaker 1 Koalas, we associate them with Australia today, and you've mentioned drop bears already. Any equivalent in the Ice Age, Ice Age Australian koalas?

Speaker 3 Koalas used to be much more diverse.

Speaker 3 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.

Speaker 3 So before these ice ages, you had much larger koalas as well.

Speaker 3 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.

Speaker 3 Australia is a story about aridification. So we often will zoom into the Pleistocene and look at the short-term impacts of aridification.
And honestly, that's what drew me to working in Australia.

Speaker 3 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?

Speaker 3 When you have extreme aridification. And that's Australia.
But Australia has also undergone aridification over millions of years. So it...
It was largely sort of more of a rainforest world earlier on.

Speaker 3 And, you know, slowly it's sort of begun to dry out and reduce the forests. But there used to be forests in

Speaker 3 areas that today are semi-arid regions. And so you've seen this transition over millions of years going from things like possums in the treetops or actually giant wombat-like animals.

Speaker 3 There were things related to diprotodons, kind of from that sort of group that were up in the trees, kind of like a...

Speaker 3 maybe like a sloth bear or a panda bear trying to get at you know fruits and in a very wet lush environment and then as things begin to dry out and this is something that's happening sort of also globally you know one of the 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 and ultimately when you isolate not just australia and 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.

Speaker 3 And that's actually contributing to sort of global cooling, right?

Speaker 3 Before that sort of water was sort of directed, you know, up into other areas, you would have warm water making it into these cooler areas.

Speaker 3 And much like 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.

Speaker 3 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.

Speaker 3 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.

Speaker 3 You get some giant, really bizarre animals on the landscape in these big grassland, more open woodland environments, as opposed to the rainforest that had sort of predominated previously.

Speaker 3 And we often refer to this shift as kind of going from like the greenhouse world to the ice house world.

Speaker 3 So, you know, Australia exemplifies all of these changes, and there's all sorts of amazing animals.

Speaker 3 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.

Speaker 1 And that, of course, also includes snakes. Were there giant Ice Age snakes, Larissa, in Ice Age Australia?

Speaker 3 There were.

Speaker 3 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.

Speaker 3 And interestingly, though, there were some really large pythons, essentially, that lived in Australia.

Speaker 3 And so imagine something a bit bigger than an anaconda, 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.

Speaker 3 You know, that's when it was really warm and these snakes could get really, really large. But it is a pretty massive snake.

Speaker 3 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.

Speaker 3 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.

Speaker 3 The venomous ones can be, you know, those are the ones I'm terrified of.

Speaker 1 Well, and you've also highlighted, Larissa, that importance in the story of Australia, I sage Australia, Australia in general, with aridification, with that

Speaker 1 climate part of the story, and we're going to get to that. But I want to talk a bit more about the evidence we have surviving for these megafauna, Larissa.

Speaker 1 I mean, how rich an archaeological record is there from Australia today? Do you have lots of sites to choose from to learn more about these megafauna and ultimately what happens to them?

Speaker 3 Yes and no. There are a fair number of sites in Australia that preserve megafauna, but there are far fewer that

Speaker 3 demonstrate coexistence of humans and megafauna. And so, and there are

Speaker 3 really none

Speaker 3 that show sort of direct evidence of humans killing, say, like a diprotodont or one of these really large animals.

Speaker 3 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 are, or were consumed until recently.

Speaker 3 And so it's quite interesting. There's, you know, this, the smoking gun of seeing, you know, these butchered sites with, you know, human artifacts and megafauna remains remains to be seen or found.

Speaker 3 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.

Speaker 3 And I think a lot of what I do and what other researchers in the area are doing is trying to understand their paleoecology and paleobiology.

Speaker 3 So before we even get to sort of what killed them off, how did they live?

Speaker 3 And

Speaker 3 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.

Speaker 3 So there's this one animal called Procoptodon golia and it's a short-faced

Speaker 3 procoptodon goliah and it's a short-faced kangaroo a goliath right it's a giant short-faced kangaroo 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,

Speaker 3 which is pretty self-evident. And so

Speaker 3 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,

Speaker 3 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.

Speaker 3 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.

Speaker 3 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.

Speaker 3 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.

Speaker 3 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.

Speaker 3 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.

Speaker 3 And those are plants that photosynthesize a little bit differently. And then we can look at the microware and say, oh, they were eating shrubs, not not grass, or they were eating grass, not shrubs.

Speaker 3 And in Australia, things get really complicated really quickly because there's such a diversity of vegetation.

Speaker 3 And, you know, when I work in places like Florida or, you know, colleagues of mine who work in places like East Africa, it's a very simple system. You have essentially C4 grasses.

Speaker 3 So when you get a C4 signal, that means the animal's eating grass. And you have C3 plants.
But in Australia, we have C3 grasses and C4 grasses. We have C3 plants and C4 C3 shrubs and C4 shrubs.

Speaker 3 And so you can't really see anything unless you're both looking at the isotopes and looking at the microware.

Speaker 3 And you're probably at this point saying, well, why do I care if an animal was eating, you know, C4 shrubs or C3 grass or what that diet was.

Speaker 3 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.

Speaker 3 So, in the case of Procopton Golia, we end up finding that they are eating C4 shrubs, and this is based on both the microware and the isotopes.

Speaker 3 What that tells us is that they're consuming saltbush, right? They're consuming a lot of this, this, this species called, or this from the genus Atrioplex.

Speaker 3 And as the name or the common name implies, saltbush has salt. 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?

Speaker 3 Which one are you going to go for if you haven't had water in the last few hours?

Speaker 1 I would probably go for an apple because an apple's got water in it.

Speaker 3 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.

Speaker 3 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 isotope. So,

Speaker 3 you know, as you are what you eat and everything is incorporated into your tissues, everything you drink is also incorporated into your tissues.

Speaker 3 And so we can actually see that peropton Golia compared to other co-occurring kangaroos has much lower oxygen isotope values, indicating that it's drinking water.

Speaker 3 It's not just getting water from plants that it's eating. So what this tells us is we have this giant C4 browser that's eating saltbush predominantly on the landscape.

Speaker 3 It's going to require water and it's going to require water at regular intervals.

Speaker 3 As the environment starts to dry out and you have increased aridification, it's going to make this animal more vulnerable to extinction.

Speaker 3 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.

Speaker 3 And so anything that has is smaller in number and occupies more space is more likely,

Speaker 3 the possibility of getting to zero through various stochastic or random processes is more likely the smaller that number is. So these are all things that make it vulnerable.

Speaker 3 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.

Speaker 3 equally likely is it could be, you know, giant chompy things, right? Crocodiles.

Speaker 3 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, you know, take advantage of the naive or the less observant prey animal that comes up to the water and doesn't see that the crocodiles there.

Speaker 1 They are one of the great animal survivors, aren't they, of all time?

Speaker 3 Yes, absolutely. And so it makes Rehopton Golia incredibly vulnerable if water sources are becoming fewer and far between, or if the risk at these water sources is increasing in any way.

Speaker 3 And so what do we see? We see them go extinct. And this gives us cause

Speaker 3 about what those drivers may be. 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.

Speaker 3 to a reduction in water on the continent.

Speaker 1 Larish, it's so interesting. And also how teeth are so important for learning more about that stuff and how much information you can ascertain from these molars or whatever that have survived.

Speaker 1 But also it seems to suggest, as you said there, we'll delve more into that climate change, the aridity part of this discussion in a moment.

Speaker 1 But I guess, does it also emphasize the fragility of many of these great megafauna species that even with a slight change in their environment, in their climate, because they're so big, you know, even small changes can set off a huge domino effect that can result in extinctions.

Speaker 3 Yes, so all things being equal, larger things are more vulnerable to extinction, at least in the present day. And we know this by studying, you know, modern animals.

Speaker 3 Animals have different ways in which they can reproduce and invest their energy, and there's constantly trade-offs.

Speaker 3 So you can either invest your energy in getting really big and also making sure your offspring have lots of resources, or you can have lots of offspring, but the chance of any one of those surviving is going to be lower.

Speaker 3 So some classic examples of this are if you think of, you know, fish, right? So fish have tons and tons of eggs.

Speaker 3 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.

Speaker 3 Alternatively, you have things on the far end of the spectrum, things like elephants, right? They have a long gestation period. They produce

Speaker 3 one offspring, much like us,

Speaker 3 during

Speaker 3 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.

Speaker 3 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?

Speaker 3 We invest quite a lot, right? Our kids are with us for 18 years.

Speaker 3 That's a long time.

Speaker 3 And, you know, we're investing in them before they sort of go off. 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.

Speaker 3 And so, when you have things that can reproduce quickly, things like rodents, rabbits, they produce lots of offspring at one time.

Speaker 3 Some of them can reproduce multiple times a year. Those things are able to sort of respond.
It's sort of a numbers game to any stochastic processes, right? Some of them might go extinct as well,

Speaker 3 but likely some of them are going to survive. But if you have you know, these really large animals and you have a variety of forces that are perturbing them, and those can be be climate change.

Speaker 3 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.

Speaker 3 And the closer you get down to zero, if you hit zero, that's it. 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.

Speaker 3 And unfortunately, the things that are the biggest in many cases today, at least, are the things that are most vulnerable to going extinct.

Speaker 1 Larissa, I'd like now to quickly talk about humans in Ice Age Australia and their relationship with these megafauna.

Speaker 1 I appreciate that Indigenous Australians believe that they've been in Australia forever. I respect that belief.
But scientifically...

Speaker 1 When do we think now, when do we believe now that the first humans reach Ice Age Australia?

Speaker 1 And for how long roughly do we think that they coexist with various Ice Age megafauna before they go extinct?

Speaker 3 Yeah, so we, 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.

Speaker 3 And they also thought that a lot of the megafauna were going extinct around this time. And so there was this sort of reigning hypothesis called the Blitzkrieg hypothesis.

Speaker 3 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.

Speaker 3 Now, we learned a lot since then. 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.

Speaker 3 And that's based on archaeological evidence found in the northern part of Australia that also show,

Speaker 3 and other sites that also show, you know, megafauna. We have some sites that show coexistence of humans and megafauna, which is really exciting.

Speaker 3 So there's a site called Lake Mongo and also a site that I worked quite extensively with, which is called Cuddy Springs. And this was a site.

Speaker 1 Ah, Cuddy Springs, yes.

Speaker 3 Yes.

Speaker 3 And Cuddy Springs is an interesting. 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.

Speaker 3 And I had no idea that, you know, Cuddy Springs at the time was as controversial as it was.

Speaker 3 And one of the reasons it was so controversial, and I say was, because we've learned a lot since, 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.

Speaker 3 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 Blitz Creek hypothesis.

Speaker 3 And so it received a lot of what I think is

Speaker 3 probably unfair scrutiny. Any site needs scrutiny.
but it was sort of not a rigorous scientific debate.

Speaker 3 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 not cut these springs out of the picture, essentially.

Speaker 3 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.
She's an archaeologist. She excavated the site for decades.

Speaker 3 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.

Speaker 3 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.

Speaker 3 And so, for example, when they said, oh, it's a mixed assemblage, everything's jumbled together. I said, well, let's test that.
So she reaches out to Clive Truman, who's an expert. on rare earths.

Speaker 3 And they use 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.

Speaker 3 And just for a long time, I think just Cuddy Springs being Cuddy Springs.

Speaker 3 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,

Speaker 3 you know, typically male archaeologists were saying at the time, I'm sure that played into it as well. But it was really contentious.

Speaker 3 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?

Speaker 3 What are these different kangaroos eating?

Speaker 3 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?

Speaker 3 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 arrive right this is the ice age australia megafauna reigning over the continent not a human in sight but then there's another layer that's much more recent around 30 000 years And so what we did is we actually looked at all of the animals that were in both of those

Speaker 3 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.

Speaker 3 Paleontologists, we're so excited to get at the big step. Archaeologists meticulously will map out the site.
And

Speaker 3 this often is now occurring in paleontological sites, but still not to the rigor and the level that archaeologists do it. But everything had been meticulously excavated.

Speaker 3 And so we knew the horizons that they were in, the rare earths had been done.

Speaker 3 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.

Speaker 3 And we know that based on modern kangaroos today.

Speaker 3 So you can look at kangaroos from really wet environments, really dry environments, and sort of in between, and you can actually use those oxygen isotopes to reconstruct the environment.

Speaker 3 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 areas or low rainfall areas.

Speaker 3 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.

Speaker 3 And once we've sort of tested that to make sure it works in the modern, we can take that back into the fossil record.

Speaker 3 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.

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Speaker 2 Dashing through the store, Dave's looking for a gift. One you can't ignore, but not the stocks he picks.
I know, I'm putting them back. Hey, Dave, here's a tip: put scratchers on your list.

Speaker 1 Oh, scratchers, good idea.

Speaker 2 It's an easy shopping trip. We're glad we could assist.
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Speaker 2 A little play can make your day.

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Speaker 1 So we're Cuddy Springs. This is New South Wales.
This is inland. This is nowhere near the coast.

Speaker 1 So you should be imagining, I mean, today, I don't know if it's outback, is it, but quite a dry landscape today when you're excavating and finding out what the environment was like for these megafauna in these different sediment layers that you said, whether it's 30,000 years ago or 400,000 years ago?

Speaker 3 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.

Speaker 3 And with that, we can also look at what the animals are eating. So the oxygen tells us about

Speaker 3 what the water is like or what the climate is like. And the carbon isotopes can tell us what exactly they were eating.
Were they eating

Speaker 3 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,

Speaker 3 what we find is that with increased aridification, so as things are getting drier, which we can see with the kangaroos, right? So the kangaroos are also demonstrating this at the site.

Speaker 3 We also see a shift away from eating C4 resources.

Speaker 3 And this is actually in contrast to what I see in Florida happening during glacial and interglacial time.

Speaker 3 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. You've got horses and and

Speaker 3 mammoths and all sorts of things that are able to eat the C4 resources. You have other things that are browsing.

Speaker 3 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.

Speaker 3 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?

Speaker 3 Well, it turns out, similar to Procopton Golaya, 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.

Speaker 3 In fact, we don't think it has. We think it's probably stayed on the landscape.

Speaker 3 But what we do are learning is that these animals are likely unable to eat those resources, eat that C4 saltbush anymore.

Speaker 3 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

Speaker 3 the continent that's happening sort of, you know, globally, but also locally, the Lake Erie Basin is drying out. You have the weakening of the monsoon signal, for example.

Speaker 3 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.

Speaker 3 And so aside from everything, I think what it was telling us is that animals are vulnerable to changes in the climate. that we do need to consider what the impacts are of aridification.

Speaker 3 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's sort of like, yeah,

Speaker 3 okay, well,

Speaker 3 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.

Speaker 3 I said, yeah, but when we published that paper, so the paper took us a while to get out.

Speaker 3 We want to make sure it was done right.

Speaker 3 I was also, I went transitioning from a grad student to a junior faculty, setting up my lab, getting the machinery and equipment to be able to properly, you know,

Speaker 3 ask and answer the questions.

Speaker 3 But when that paper came out about a week prior, the paper came out that said, so in 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.

Speaker 3 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, glycosine, Australia, New Guinea, megafauna to climate environmental change, and talked about those impacts.

Speaker 3 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.

Speaker 3 And this is from the Lake Mungo Walandra Lakes site that was led in the paper that was led by Michael Westaway.

Speaker 3 But essentially, they demonstrated another site that showed an animal called Zygomaturus and megafauna coexisting for some period of time.

Speaker 3 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.

Speaker 3 You now have an additional site that's showing prolonged coexistence.

Speaker 3 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.

Speaker 3 And so we're starting to see this sort of more complete picture of

Speaker 3 what's sort of happening, in which case there might be more prolonged coexistence of humans, a variety of causal factors.

Speaker 3 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 why these were going extinct.

Speaker 1 So interesting, isn't it, how this new research is revealing more and more and more. And as you say, that the duration of coexistence between early humans in Australia and megafauna,

Speaker 1 it's going further back and back, which is really interesting. And Zygomaturus, I mean, that's another of those big Ice Age wombat things, isn't it?

Speaker 3 Yes, yes. Related to Diprotodon, it's maybe more of a forested dweller.
There's some different hypotheses there.

Speaker 3 But yes, it's a maybe think of a smaller rhino size or a large taper size, but still quite large.

Speaker 1 So what your research is revealing is that with that changing climate, it evidently does affect the diets of these megafauna, as is shown through the scientific research of their teeth at sites like Cuddy Springs and so on.

Speaker 1 I am always hesitant when people say, oh,

Speaker 1 certain large species died out for one reason, and newspaper headlines are saying they died out because of this.

Speaker 1 Do you think, yes, climate probably was a significant factor in the ultimate extinction of many of these species, but can we not rule out that some of these early humans did hunt them or at least presumably scavenged the remains of these big beasts?

Speaker 1 And maybe could that have had a small impact too?

Speaker 3 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.

Speaker 3 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.

Speaker 3 So, for example, and I'm going to transition to a different continent, in North America, I was part of a team that did a very large study that came out in Science in 2023 about

Speaker 3 the megafaunal extinction, the timing of it at La Brea.

Speaker 3 And

Speaker 3 there,

Speaker 3 the data look as if the megafauna at La Brea, at least, are going extinct locally right about the same time when

Speaker 3 fire frequency is skyrocketing. And I mean skyrocketing.
It's going from minimal amounts of charcoal to a huge spike. I don't know how better to explain it.
It's literally just jumping in magnitude.

Speaker 3 And so there, we don't know. We don't know, was it humans who are lighting these fires? Presumably, this is at the same time when humans are increasing their prevalence in these areas.

Speaker 3 We do know that they used fire, but it's something that you can't ignore, right? The humans very well may have played a large role in altering the ecosystems in North America.

Speaker 3 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 the compelling.

Speaker 3 And so there's no like clear evidence. There's only a few sites that show coexistence.
And it is possible, of course.

Speaker 3 And I think, but I think what's happening is the rating hypothesis for so long has been one of humans coming onto the continent.

Speaker 3 you know, killing off everything very quickly, and then iterations of that hypothesis just keep getting, you know, stretched thinner and thinner and thinner.

Speaker 3 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?

Speaker 3 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.

Speaker 3 Presumably, if it is just humans, if human overhunting was the cause of

Speaker 3 these megafaunal extinctions, then if we stop hunting these animals, then presumably

Speaker 3 everything will be fine, right? That these animals would be able to respond positively and you remove that factor.

Speaker 3 But if climate change played any role, whether that was a synergistic role, whether that was the, you know, 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.

Speaker 3 And so,

Speaker 3 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.

Speaker 3 And the more and more I, you know, I investigate these different animals, whether it's the

Speaker 3 giant shirt-faced kangaroo that was eating seafloor shrubs and

Speaker 3 eating saltbush and requiring water, or the one I didn't really get to talk to, talk about much yet is the marsupial lion that we think was actually hunting

Speaker 3 just from things from forests. And so we know that based on the isotopes, and we've looked at the microware of these, they have bolt cutters for teeth.

Speaker 3 They could eat whatever they wanted, but they are only eating things

Speaker 3 actually within these dense forests. And so what that tells me is that when environments

Speaker 3 are getting drier and opening up and fewer forests, 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.

Speaker 3 These forest browsers are also disappearing from these ecosystems.

Speaker 3 And so in the case of, you know, the marsupial lion or killer wombat, whatever you want to call it, you know, it's no match for climate change.

Speaker 3 And so I think we have to just, you know, I think we have to remain open and

Speaker 3 know, continue to evaluate all of the different hypotheses. And to, you know, on that note, I remain open about looking at the impacts of humans.

Speaker 3 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.

Speaker 3 I think I should make that clear. I'm a paleontologist.

Speaker 3 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 of the time.

Speaker 3 But it may be a bit different than, say, some of the other guests you've had on for other shows where, you know, the archaeologists are

Speaker 3 kind of working within a much more recent timeframe.

Speaker 3 But

Speaker 3 one of the things I was just going to mention is that the First Nations people today, at least, have a very different

Speaker 3 concept of sort of wildlife management than we do. And it's this concept of country.

Speaker 3 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

Speaker 3 biological entities on the planet. no more or less than anything else.

Speaker 3 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.

Speaker 3 And this was an animal that they would not consume, but it was an animal that they also would try to manage, right?

Speaker 3 And they would be knowledgeable about if the population was increasing or decreasing. And so, you know, I think there's a lot more work.

Speaker 3 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.
But

Speaker 3 there's a lot that I think I, you know, we don't fully understand

Speaker 3 with sort of how people were managing or respecting their environment. And also, we need to kind of consider those factors.

Speaker 3 We can't just take the sort of Western view of conquering, bring it to Australia

Speaker 3 and say, therefore, megafauna went extinct, we need to kind of step back, really evaluate and be open to other hypotheses.

Speaker 1 Larissa, this has been fantastic. I'm afraid we can't talk in any more detail about the marsupial lion or killer wombat, but what a species that is.

Speaker 1 Last but certainly not least, I mean, briefly tell us about the research center that you created, the DeSantis Dream Lab, what it is and why it's important and linked to your research.

Speaker 3 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

Speaker 3 how mammals have responded to climate change in the past.

Speaker 3 And there's actually an entirely new field that sort of developed within the past few decades, which is referred to as conservation paleobiology.

Speaker 3 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.

Speaker 3 So, we try to look at which animals responded to these climate changes or what were the impacts of these extinctions.

Speaker 3 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?

Speaker 3 And so, I study mammals broadly. I love working in Australia.
I love sort of studying them experiencing some of the most arid conditions.

Speaker 3 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 of these fires.

Speaker 3 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 extract.

Speaker 3 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.

Speaker 3 I primarily work in North America and in Australia, although I have colleagues and collaborations on all continents except for Antarctica.

Speaker 1 Larissa, this has been absolutely fantastic. It just goes to me to say thank you so much for taking the time to come on the podcast today.

Speaker 3 Thanks so much for your interest in this topic and for having me.

Speaker 1 Well, there you go. There was Professor Larissa DeSantis giving you an introduction to the amazing world that was Ice Age Australia.
I hope you enjoyed the episode.

Speaker 1 Next week we're moving from Ice Age Australia to Europe and Western Asia to explore the story of the last Neanderthals.

Speaker 1 That episode featuring Dr. Chris Stringer promises to be a big one, so stay tuned.
In the meantime, please follow this show on Spotify or wherever you get your podcasts.

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