Ice Age Australia

Giant kangaroos. Killer wombats. Carnivorous lions. These beasts once roamed the barren landscape of Ice Age Australia - a vast supercontinent stretching from Papua New Guinea to Tasmania. Continuing our Ice Age miniseries, host of The Ancients Tristan Hughes heads down under to uncover this lost world. Joined by palaeontologist Prof. Larisa DeSantis, he explores how these creatures survived both the challenges of a harsh climate and the arrival of humans 60,000 years ago, and discovers why Australia’s mammalian giants ultimately vanished. Presented by Tristan Hughes. Audio editor is Aidan Lonergan, the producer is Joseph Knight. The senior producer is Anne-Marie Luff. All music courtesy of Epidemic Sounds The Ancients is a History Hit podcast. Sign up to History Hit for hundreds of hours of original documentaries, with a new release every week and ad-free podcasts. Sign up at https://www.historyhit.com/subscribe. You can take part in our listener survey here https://insights.historyhit.com/history-hit-podcast-always-on: https://insights.historyhit.com/history-hit-podcast-always-on Hosted on Acast. See acast.com/privacy https://acast.com/privacy for more information.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Tristan Hughes?

  Ever wondered why the Romans were defeated in the Teutoburg Forest? What secrets lie buried in prehistoric Ireland? Or what made Alexander truly great? With a subscription to History Hit, you can explore our ancient past alongside the world's leading historians and archaeologists. You'll also unlock hundreds of hours of original documentaries with a brand new release every single week, covering everything from the ancient world to World War II. Just visit historyhit.com/subscribe.

• 0:32Speaker 01

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• 1:02Speaker 02

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• 1:19Tristan Hughes?

  This episode is sponsored by Smart Travel, a new podcast from NerdWallet. Now, you know that one friend who always finds the best travel deals, picks the right cars, and somehow ends up in first class for the price of coach. Smart Travel is like that friend, but in podcast form. They cover all things travel finance, so you can stop stressing and actually start enjoying your trips. I'm lucky enough to travel a fair bit. You might have heard me talking about being on tour with The Ancients in Australia and New Zealand quite recently. Well, Smart Travel Podcast from NerdWallet was a great help. They dig into which airport lounges are really worth it and which are just an airport

• 2:01Tristan Hughes?

  gate with better snacks and worse lighting, and what actually happens when an airline loses your luggage for 12 days, and how to get real money back instead of a free drink and an apology. Plus, the tip I really needed: how to book flights without it turning into a part-time job. Travel smarter and spend less with help from NerdWallet. Follow Smart Travel wherever you get your podcasts.

• 2:45Tristan Hughes?

  The woolly mammoth, the saber-toothed tiger, the giant ground sloth. 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. But what about the Procoptodon goliath, a giant short-faced kangaroo? Or the Diprotodon, a massive herbivorous marsupial also known as the killer wombat? Or perhaps the Wenambi, 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. It's The Ancients on History Hit.

• 3:28Tristan Hughes?

  I'm Tristan Hughes, your host. Today, we're exploring the extraordinary world of Ice Age Australia. 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. Our guest today is Professor Larisa DeSantis from Vanderbilt University. 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. Larissa has examined how climate change may well have contributed to the extinction of these giant kangaroos, killer wombats, flightless birds, and so on.

• 4:10Tristan Hughes?

  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.

• 4:22Tristan Hughes?

  Marissa, it is such a pleasure to have you on the podcast today.

• 4:25Speaker 03

  Thanks so much for having me.

• 4:27Tristan Hughes?

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

• 4:46Speaker 03

  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.

• 4:57Tristan Hughes?

  And is it just Australia at the time of the Ice Age, or should we be thinking bigger?

• 5:03Speaker 03

  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 glaciers 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. 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. 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.

• 5:46Speaker 03

  And so all that was considered one large sort of landmass because the continental shelf was exposed and all of those areas were much, the sea level was lower. And so animals could literally, and people could walk back and forth as needed.

• 6:00Tristan Hughes?

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

• 6:07Speaker 03

  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 pathways are cut off or whatever species that might be. And other periods where they're connected. 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.

• 6:35Tristan Hughes?

  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?

• 6:45Speaker 03

  Sure, yeah, they're pretty standard and largely caused by sort of orbital cycling. And so the the Milankovic 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 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. But you typically go from a period of pronounced glaciers and then all you start having, you know, the warming, the melting of the ice that's going to cause sort of a the warming in general of other surrounding areas. You have these positive

• 7:26Speaker 03

  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 you just kind of go from cycle to cycle between glacial and interglacials.

• 7:43Tristan Hughes?

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

• 7:54Speaker 03

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

• 8:00Tristan Hughes?

  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?

• 8:17Speaker 03

  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 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

• 8:57Speaker 03

  date specimens. 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, 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. 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

• 9:39Speaker 03

  well fall in that area. It might be much older. And so it's hard to know exactly.

• 9:45Tristan Hughes?

  Now, you mentioned also in that explanation, Larissa, radiocarbon dating. So this is a, it's 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?

• 10:02Speaker 03

  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. And so after 5,000 years, half of that product has been converted or has, you know, 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

• 10:47Speaker 03

  to be able to measure it. And then there's no more. And so essentially, when we're doing any carbon dating, we are fundamentally limited. Through the last roughly about fifty thousand years, forty thousand 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 other, you know, a lot of times when you hear about pretty metric 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

• 11:31Speaker 03

  at different rates. And 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. And we don't have, you know, a lot of the volcanic ash layer and events, especially in the late Pleistocene.

• 11:47Tristan Hughes?

  Well, it's very commendable for for yourself and others in the field then who are analyzing sediments or whatever for those sites which are older than fifty thousand years ago. 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. 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. But can you give us an idea of what types of great beasts of megafauna existed in Ice Age Australia?

• 12:25Speaker 03

  Sure. There was all sorts of amazing animals. The 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. And on that image, you get to see some of the classic ones. You get to see diprotodonts, which are giant wombat-like animals the size of rhinos.

• 12:49Tristan Hughes?

  Giant rhino-sized wombats. Wow.

• 12:52Speaker 03

  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, you know, several meters in height. You would be looking eye to eye or actually looking up at them in many cases. We also had things like giant goannas. So if you think of You know, sort of the the the guanas that you might see in Australia today, imagine them the size of a saltwater crocodile.

• 13:29Tristan Hughes?

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

• 13:34Speaker 03

  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 Jenny Ornes, much more massive. 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. And I haven't even mentioned what I think is the coolest, the most interesting and most exciting, one

• 14:13Speaker 03

  of my favorites is actually often referred to as the marsupial lion. But I have a colleague who actually refers to it from a much cooler name, and that name is a killer wombat.

• 14:25Tristan Hughes?

  A killer wombat, amazing.

• 14:27Speaker 03

  Killer wombat. And it's 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? It's they're a bear. They're related to grizzly bears and black bears and polar bears, things that primarily need or are more omnivorous. 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 the largest mammalian predator in Australia. And it's always kind

• 15:12Speaker 03

  of funny because, you know, the the Australians like to scare the tourists and talk about these things called drop bears.

• 15:19Tristan Hughes?

  Oh, yes.

• 15:20Speaker 03

  I don't know if you've ever heard of this.

• 15:22Tristan Hughes?

  Oh, yes, I was in I was in Australia for a year or so. I heard the drop bears stories, yeah.

• 15:26Speaker 03

  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. 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

• 16:07Speaker 03

  in the densest of the forests. And so they relied on these trees to do their hunting. And in fact, what we're sort of learning about them, and I can go into sort of the 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 environment.

• 16:52Tristan Hughes?

  I mean, Larissa, you mentioned your work around climate change, and we're going to get to that, especially when we get to that question around extinction. And also with the arrival of humans, we're going to get to that as this chat progresses. 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, the environment that they were best suited to, I mean, do we know much about the climate, the environment in Ice Age Australia? 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?

• 17:35Speaker 03

  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, of animals living there that would have required forested ecosystem. So what we do know is that they likely experienced fairly extreme environmental fluctuations, right? So going from, you know, 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.

• 18:17Speaker 03

  And I think often people sort of underestimate the role that extreme heat and drought can play on an ecosystem, 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, there were, a lot of things were bigger, right? So you had, you know, we talked about the, you know, Diprotodon, the giant wombat-like animal the size of a rhino, but you had several different types of those. You had another one called Zygomaturus, and you had another one that was sort of like a taper a little bit, although maybe it was more like a sloth is now we're learning.

• 19:02Speaker 03

  And so you had lots of these large animals. 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, is difficult, a type of vegetation that's difficult to eat today, primarily because it has lots of salt. The salt bush is, you know, has salt and requires you drinking a lot of water. 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.

• 19:43Speaker 01

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• 20:16Speaker 04

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• 21:13Tristan Hughes?

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

• 21:22Speaker 03

  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. 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. 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.

• 22:06Speaker 03

  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. 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

• 22:48Speaker 03

  possums in the treetops, or actually giant, you know, wombat-like animals. 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 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

• 23:30Speaker 03

  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 of glaciers and ice. And that's actually contributing to sort of global cooling, right? Before, that sort of water was sort of directed, you know, up into other areas. You'd have warm water making it into these these cooler areas. And much like, you know, today, you could 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.

• 24:13Speaker 03

  And when you have this separation, we think from South America and Antarctica, 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 landscape in these big grassland, more open woodland environments as opposed to the rainforest that has 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, there's all sorts of amazing animals.

• 24:58Speaker 03

  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.

• 25:09Tristan Hughes?

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

• 25:17Speaker 03

  There were. You know, it's interesting because that's something that you wouldn't necessarily expect to get a lot larger. We, 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, not quite as big or not nearly as big as, you know, the, the Titanoboa, which is a, a Paleocene or age 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

• 26:01Speaker 03

  found in a, in a few sites in, in the southern part of Australia. Yeah, I wouldn't want to be near it, 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, those are the ones I'm terrified of.

• 26:23Tristan Hughes?

  Well, and you've also highlighted, Larissa, that importance in the story of Australia, Ice Age Australia, Australia in general with aridification, with that, that 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. 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?

• 26:58Speaker 03

  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 so, 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. 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.

• 27:42Speaker 03

  And, and so it's quite interesting. There's, you know, the, 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, the causal factors are to the extinction. And, and we've, we've talked about some of the different animals. And, and I think, you know, a lot of what, what I do and what other researchers in the area are doing is trying to understand their pale ecology and paleobiology. So before we even get to sort of what killed them off, how did they live?

• 28:22Speaker 03

  And thinking about that, would they be vulnerable to these, these changes? And so Not to kind of go back a little bit, but to kind of feature one animal. So there's this one animal called Procoptodon Goliath, and it's a a short-faced kangaroo. Sorry, what was that? Procoptodon Goliath, 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 browse, which are things like leaves, in contrast to grass, which, which is pretty self-evident.

• 29:04Speaker 03

  And so when, when researchers started actually kind of looking at the isotopic signatures, 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, you can use morphology or what you look like to infer diet, and that's one approximation. If people did an approximation of, of our diets, we would be omnivores. We are the classic omnivores. We have teeth that are ideal for, you know, brushing 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,

• 29:48Speaker 03

  lots of steak and someone else might be vegan. And those are all, you know, variation and, 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. 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.

• 30:31Speaker 03

  And then we can look at the microwear and say, oh, this, they were eating shrubs, not grass, or they were eating grass, not shrubs. And in Australia, things get really complicated really quickly because there's such a diversity of, of vegetation and You know, I work in places like Florida or, you know, colleagues who of mine who work in places like East Africa. It's a very simple system. You have essentially C4 grasses. So the gra- so when you get a C4 signal, that means the animal's eating grass. And you have C3 plant. But in Australia, we have C3 grasses and C4 grasses. We have C3 plants and C4, C3 shrubs and C4 shrubs.

• 31:13Speaker 03

  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, you know, C4 shrubs or C3 grass or what that diet was. And, 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 Proctognia, 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 salt bush, right? They're consuming a lot of this, this, this species called, or this, from the genus Atrix.

• 31:58Speaker 03

  And as the name or the common name implies, salt bush 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? Which one are you going to go for if you haven't had water in the last few hours?

• 32:12Tristan Hughes?

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

• 32:15Speaker 03

  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 and 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, you know, as, 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 Proctognia compared to other co-occurring kangaroos has much lower oxygen isotope values, indicating that's drinking water. It's not just getting water from plants that it's eating. So what this tells us is you have this giant.

• 33:00Speaker 03

  C4 browser that's eating salt bush 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 a ridification, it's going to make this animal more vulnerable to extinction. 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 has a smaller in number and occupies, you know, more space is more likely, you know, the, the possibility of getting to zero through various stochastic or random processes is more likely the smaller, you know, that number is.

• 33:45Speaker 03

  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 choppy things, right? Crocodiles. You see that as things are getting water at watering holes, whether that's in, you know, Africa or in Australia, crocodiles are more than happy to, you know, take advantage of the, the naive or the less observant prey animal that comes up to the water and doesn't see the, the crocodiles there.

• 34:22Tristan Hughes?

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

• 34:25Speaker 03

  Yes, absolutely. And so it makes for Haptongolaya 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 pause 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 to a reduction in water on the continent.

• 35:04Tristan Hughes?

  Um, Larissa, 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. 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. But I guess, does it also emphasize the fragility of many of these great megafauna species that even with, you know, 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 extinction?

• 35:44Speaker 03

  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, you know, 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. 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.

• 36:25Speaker 03

  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. Alternatively, you have things on the, you know, the far end of the spectrum, things like, you know, elephants, right? They have a long gestation period, they produce, you know, one offspring, much like us, during their, their, their 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, 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.

• 37:08Speaker 03

  And in humans are, you know, obviously one of the, 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, we're investing in them before they sort of go off. But even so, even if it was, even at the slightly younger ages, 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, they, 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?

• 37:51Speaker 03

  Some of them might go extinct as well, 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, 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. And the more, the closer you get down to zero, if you hit zero, that's it. You even hit one, that's it, right? And so you can't reproduce and you can never recover from that. So it's, it's really a numbers game. And unfortunately, the things that are the biggest in many cases today at least,

• 38:36Speaker 03

  are the things that are most vulnerable to going extinct.

• 38:40Tristan Hughes?

  Larissa, I'd like now to quickly talk about humans in Ice Age Australia and their relationship with these megafauna. I appreciate that Indigenous Australians believe that they've been in Australia forever. I respect that belief, but scientifically, when do we think now? When do we believe now that the first humans reach Ice Age Australia? And for how long roughly do we think that they coexist with various Ice Age megafauna before they go extinct?

• 39:11Speaker 03

  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. 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. 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. And one of the

• 39:54Speaker 03

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

• 40:27Tristan Hughes?

  Ah, Cuddy Springs, yes.

• 40:29Speaker 03

  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, 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, 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

• 41:14Speaker 03

  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. 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, it's a mixed assemblage. And, and the woman who has done so much for the site is Jude Field. She's an archaeologist. She excavated the

• 41:57Speaker 03

  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, and really did a lot of remarkable work. But, you know, anytime there was sort of contentious issue, she would go out and find the best person to help sort of test that question. 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 earth. And they use rare earth, which is a kind of a way of looking at different chemical signatures and in fact

• 42:38Speaker 03

  shows, no, we have these sort of intact assemblages. And just for a long time, I think just Cuddy Springs being Cuddy Springs. And, 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, the, you know, typically male archaeologists were, were saying at the time. I'm, I'm sure that played into it as well. But it was really contentious. 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, you know, what are these different

• 43:19Speaker 03

  kangaroos eating? What are, you know, we have these ideas based on their morphology, but, but what is their diet? And what can we tell about these animals? So when I went over there, I was really interested in looking at the change from, so there is 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, megafaunal raining 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.

• 44:04Speaker 03

  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 at the big step. Archaeologists meticulously will map out the site. And 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. And so we knew the horizons that they were in, that rare earths had been done. 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.

• 44:48Speaker 03

  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. 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. 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.

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• 47:09Tristan Hughes?

  So we cut east springs. This is New South Wales. This is inland. This is nowhere near the coast. 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.

• 47:30Speaker 03

  Yes, absolutely. So as you're kind of comparing the different layers, we can see this sort of shift in the oxygen isotopes. 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. 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?

• 48:15Speaker 03

  So the kangaroos are also demonstrating this at the site. We also see a shift away from eating C4 resources.

• 48:24Speaker 03

  And this is actually in contrast to what I see in Florida happening, you know, during glacial, interglacial time. So when you go from sort of a forested ecosystem to this B4, 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 manas and, 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.

• 49:04Speaker 03

  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 Precocton Goliath, the short-faced kangaroo, many of these C4 resources are things like salt bush. And so we don't know if the salt bush has gone away. In fact, we don't think it has. 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 salt bush 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

• 49:47Speaker 03

  happening, sort of, you know, globally, but also locally, the Lake Eyre Basin is, is drying out. You have the weakening of the monsoons 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 aridification. 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, okay. Well, what, what, what new, what new thing are you telling us?

• 50:32Speaker 03

  Like, this doesn't seem earth shattering or groundbreaking. You know, the animals are vulnerable to climate change. Said, yeah, but when we published that paper, the paper took us a while to get out. It was, we want to make sure it was done right. We, I was also, I went transitioning from a grad student to junior faculty setting at my lab, getting the machinery and equipment to be able to properly, you know, and ask and answer the questions. 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.

• 51:14Speaker 03

  And then our paper came out about a week later and said, didn't say anything about causal factors, but said dietary responses of Sahel, Pleistocene Australia, New Guinea, megafauna to climate and environmental change, and talked about those impacts. 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 Wollongong Lakes site that was led, and the, and the paper that was led by Michael Westaway. But essentially, they demonstrated another site

• 51:57Speaker 03

  that showed an animal called Zygomaturus 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. 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

• 52:34Speaker 03

  Of what's sort of happening, in which case there might be, you know, more prolonged coexistence of humans, a variety of causal factors. But I think it just goes to show the importance of actually kind of stepping back and trying to understand just even the paleontology 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.

• 52:56Tristan Hughes?

  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, 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?

• 53:16Speaker 03

  Yes, yeah, it's related to dichotodon. It's maybe more of a forested dwellers, some different hypotheses there. But, uh, yes, it's a, maybe think of a smaller rhino size or a, uh, large tapir size, but still quite large.

• 53:31Tristan Hughes?

  So what your research is revealing is that with that change in 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. I am always hesitant when people say, oh, certain large species died out for one reason, and newspaper headlines are saying they died out because of this. 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? And maybe could that have had a small impact, too?

• 54:16Speaker 03

  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 not 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 the megafaunal extinction, the timing of it at La Brea. And

• 54:51Speaker 03

  There, the data look as if the megafauna, at least 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 a huge spike. I don't know if I'm 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?

• 55:33Speaker 03

  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, like, clear evidence. There's only a few sites that show coexistence. And it is possible, of course. And I think, but I think what's happening is the reigning hypothesis for so long has

• 56:11Speaker 03

  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? 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 extinction. Then if we stop hunting these animals, then presumably, everything will be fine, right?

• 56:55Speaker 03

  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, 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. 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.

• 57:37Speaker 03

  And the more and more I, you know, I investigate these different animals, whether it's the, you know, giant chirphea kangaroo that was eating seaford shrubs and eating salt bush 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. And so we know that based on the isotopes and we've looked at the microwear of these. 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

• 58:22Speaker 03

  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. These forest browsers are also disappearing from these ecosystems. 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. And so I think we have to just, you know, I think we have to remain open. And you 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.

• 59:01Speaker 03

  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. I think, oh, 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 of the time. But it maybe it's a bit different than, say, some of the other guests you've had on for other shows, where, you know, the archaeologists are, are kind of working within a much more recent timeframe.

• 59:39Speaker 03

  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. 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. A few of the things that that I've become aware of or learned about are things like totems

• 1:00:23Speaker 03

  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 would try to manage, right? And they would, 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. But there's, there's a lot that I think.

• 1:01:01Speaker 03

  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.

• 1:01:19Tristan Hughes?

  Yes.

• 1:01:19Speaker 03

  And say, therefore megafauna went extinct. We need to kind of step back, really evaluate, and be open to other head economies.

• 1:01:28Tristan Hughes?

  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. 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.

• 1:01:49Speaker 03

  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 paleo biology. 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, you know, look at which animals, you know, responded to these climate changes, or what were the impacts of these extinctions?

• 1:02:31Speaker 03

  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. 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.

• 1:03:13Speaker 03

  To extract important sort of conservation lessons and even cautionary lessons that can be of relevance 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.

• 1:03:33Tristan Hughes?

  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.

• 1:03:39Speaker 03

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

• 1:03:45Tristan Hughes?

  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. Next week, we're moving from Ice Age Australia to Europe and Western Asia to explore the story of the last Neanderthals. 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. It really helps us and you'll be doing us a big favour. Don't forget, you can also listen to us and all of History Hits podcasts ad-free and watch hundreds of TV documentaries when you subscribe at historyhit.com/subscribe.