Ice Age Australia

Summary

The Ancients: Episode Summary – Ice Age Australia

Podcast Information:

• Title: The Ancients
• Host: Tristan Hughes
• Guest: Professor Larissa Desantis, Vanderbilt University
• Episode: Ice Age Australia
• Release Date: February 9, 2025
• Description: Delving into the distant past, this episode explores the extraordinary world of Ice Age Australia, examining its unique megafauna, climatic shifts, human arrival, and the factors leading to the extinction of its magnificent beasts.

---

Introduction to Ice Age Australia

Tristan Hughes opens the episode by setting the stage for an exploration of Ice Age Australia, a period marked by significant climatic fluctuations and the presence of diverse megafauna. He introduces Professor Larissa Desantis, a renowned paleontologist specializing in Australian megafauna, as the guest who will shed light on the fascinating and less commonly discussed aspects of Australia’s ancient past.

Tristan Hughes:
"When someone mentions the Ice Age, you might immediately think of great beasts like woolly mammoths or saber-toothed tigers. But Ice Age Australia was home to equally extraordinary and unique megafauna."
(00:31)

---

Climatic Conditions and Landmass Configuration

Professor Desantis elaborates on the Pleistocene epoch’s climatic cycles, emphasizing the global nature of glacial and interglacial periods. She explains how lower sea levels during glacial maxima connected Australia, Papua New Guinea, and Tasmania into a single landmass known as Sahul. This connection facilitated the movement of both humans and animals across these regions.

Professor Larissa Desantis:
"The Pleistocene was defined by cycles of glacial and interglacial periods, leading to significant fluctuations in sea levels. During glacials, Sahul emerged as a vast landmass, allowing animals and humans to traverse what are now separate islands."
(05:16)

---

Diverse Megafauna of Ice Age Australia

The discussion transitions to the remarkable array of megafauna that inhabited Ice Age Australia. Desantis highlights species such as the Procoptodon goliah, a giant short-faced kangaroo, and the Diprotodon, often referred to as the "killer wombat." Additionally, she mentions massive snakes akin to today’s pythons and formidable flightless birds.

Professor Larissa Desantis:
"We had diprotodons, giant wombat-like animals the size of rhinos, and Procoptodon goliah, a kangaroo several meters tall. There were also massive snakes and formidable flightless birds that dominated the landscapes."
(12:09)

---

Challenges in Dating and Fossil Preservation

One of the significant hurdles in studying Ice Age Australia’s megafauna is accurately dating the fossils. Radiocarbon dating is limited to specimens younger than approximately 50,000 years, and many Australian fossils exceed this age. As a result, alternative dating methods, such as potassium-argon dating, are employed, although they offer less precision.

Professor Larissa Desantis:
"Radiocarbon dating is only effective for fossils up to about 50,000 years old. Many Australian megafauna fossils are older, necessitating the use of other dating methods, which are less precise."
(09:46)

---

Human Arrival and Coexistence with Megafauna

The episode delves into the arrival of humans in Australia around 65,000 years ago and their coexistence with the continent’s megafauna. Desantis discusses archaeological sites like Cuddy Springs and Lake Mungo, which provide evidence of humans and megafauna existing concurrently for thousands of years.

Professor Larissa Desantis:
"Sites like Cuddy Springs and Lake Mungo have demonstrated prolonged coexistence between humans and megafauna, challenging the earlier blitzkrieg hypothesis that humans rapidly drove these species to extinction shortly after their arrival."
(38:54)

---

Debating Extinction Causes: Climate Change vs. Human Impact

A central theme of the episode is the debate over what led to the extinction of Ice Age Australia’s megafauna. While earlier theories, such as the blitzkrieg hypothesis, posited that humans swiftly hunted these animals to extinction, Desantis presents evidence suggesting that climate change played a more substantial role. She argues that the increasing aridification and environmental stressors made survival difficult for specialized megafauna.

Professor Larissa Desantis:
"Our research indicates that climate change, particularly the drying trend and increasing aridity, significantly impacted these megafauna. This environmental stress likely made these species more vulnerable to extinction, regardless of human presence."
(34:05)

---

Dietary Insights Through Isotopic Analysis

Desantis explains how isotopic analysis of fossilized teeth provides insights into the diets and environmental adaptations of megafauna. For instance, the study of Procoptodon goliah revealed a shift from consuming C4 shrubs like saltbush to other resources as the climate became drier. This dietary shift indicates increased vulnerability as preferred food sources dwindled.

Professor Larissa Desantis:
"By analyzing the carbon and oxygen isotopes in Procoptodon goliah’s teeth, we discovered a shift in their diet from C4 shrubs to more limited resources, reflecting the increasing aridification and reduced availability of their preferred food sources."
(31:03)

---

Unique Vulnerabilities of Large Megafauna

The episode highlights how the size and specialized niches of large megafauna made them particularly susceptible to environmental changes. Larger animals typically have slower reproduction rates and require more resources, making them less adaptable to rapid climate shifts compared to smaller, more adaptable species.

Professor Larissa Desantis:
"Larger animals like diprotodons produced fewer offspring and required extensive resources. This made them less resilient in the face of rapid climate changes and habitat loss, increasing their likelihood of extinction."
(35:27)

---

Conservation Lessons from the Past

Desantis introduces her research center, the Desantis Dream Lab, which focuses on conservation paleobiology. The lab aims to understand how past climate changes affected mammalian ecosystems to inform current conservation strategies. By studying ancient responses to environmental stressors, the research provides valuable lessons for protecting modern biodiversity.

Professor Larissa Desantis:
"Our Dream Lab is dedicated to understanding how mammals responded to past climate changes. This research is crucial for developing effective conservation strategies today, as it offers insights into how current species might cope with ongoing environmental challenges."
(61:01)

---

Indigenous Knowledge and Wildlife Management

The conversation also touches on the importance of integrating Indigenous Australian knowledge into scientific research. Desantis emphasizes the value of traditional practices, such as totemic relationships and land management techniques, which have sustained Australia’s ecosystems for millennia.

Professor Larissa Desantis:
"Indigenous Australians have a profound understanding of wildlife management through practices like totemism and sustainable land stewardship. Collaborating with First Nations people enriches our scientific perspectives and fosters more holistic conservation approaches."
(59:30)

---

Conclusion and Future Directions

Tristan Hughes wraps up the episode by summarizing the key insights from the discussion. The exploration of Ice Age Australia reveals a complex interplay between climate change and human activities in shaping the continent’s ecological history. Desantis underscores the importance of ongoing research and collaboration with Indigenous communities to fully comprehend and preserve Australia’s natural heritage.

Tristan Hughes:
"Today's exploration into Ice Age Australia has unveiled the intricate factors that led to the rise and fall of its magnificent megafauna. As we continue to study these ancient ecosystems, the lessons we learn are invaluable for today's conservation efforts."
(62:58)

---

Looking Forward

Hughes previews the next episode, which will delve into the story of the last Neanderthals in Europe and Western Asia, featuring Dr. Chris Stringer. He encourages listeners to subscribe and stay tuned for more compelling narratives from the annals of history.

Tristan Hughes:
"Next week, we're moving from Ice Age Australia to Europe and Western Asia to explore the story of the last Neanderthals with Dr. Chris Stringer. It promises to be an enlightening episode, so stay tuned."
(63:50)

---

Notable Quotes

• Tristan Hughes:
  "We often underestimate the role that extreme heat and drought can play on an ecosystem. It's definitely having an effect and may set thresholding events where certain animals just can't survive."
  (17:19)

• Professor Larissa Desantis:
  "When we look at the oxygen isotopes and see that Procoptodon goliah has much lower values, it indicates that it was drinking water regularly. This reliance makes it more vulnerable as water sources become scarce."
  (32:29)

• Professor Larissa Desantis:
  "If climate change played a role in the past, that's crucial to understand for managing ecosystems today. It’s not just about mitigating human impact but also about preparing for how species respond to environmental stressors."
  (56:34)

---

Final Thoughts

"Ice Age Australia" offers a comprehensive look into a lesser-known chapter of ancient history, highlighting the unique challenges and adaptations of its megafauna. Through Professor Desantis's expertise, listeners gain a deeper appreciation for the intricate balance between climate, ecology, and human influence that has shaped Australia's natural world.

For more in-depth documentaries and ad-free podcasts, listeners are encouraged to subscribe to History Hit at historyhit.com/subscribe.

Transcript

[Tristan Hughes]

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[Larissa Desantis]

All About Petra and the Nabateans, and enjoy a new release every week.

[Tristan Hughes]

Sign up now by visiting historyhit.com subscribe.

[Ryan]

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[Dan Snow]

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[Ryan]

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[Larissa Desantis]

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[Larissa Desantis]

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[Tristan Hughes]

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[Larissa Desantis]

The woolly mammoth, the saber toothed.

[Tristan Hughes]

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 goliah, a giant short faced kangaroo? Or the Diprotodon, a giant carnivorous marsupial, also known as the killer wombat or perhaps the wonambi, 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 the ancients on history hit. 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 Larissa 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. 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.

[Larissa Desantis]

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

[Dan Snow]

Thanks so much for having me.

[Larissa Desantis]

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.

[Unknown]

Absolutely. And it still had a lot of.

[Dan Snow]

The large effects that we faced across the globe. You know, the Ice Age phenomenon was.

[Unknown]

Really a global phenomenon, not a localized phenomenon.

[Larissa Desantis]

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

[Unknown]

So the entire Pleistocene, which is the.

[Dan Snow]

Last 2.6 million years, is really defined.

[Unknown]

As occurring during periods of glacial interglacial period. So you have these sort of cycles.

[Dan Snow]

From full glacials where you have extensive.

[Unknown]

Ice sheets in different regions of the.

[Dan Snow]

World, much lower sea levels.

[Unknown]

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.

[Dan Snow]

So at the time that Australia was experiencing full glacial periods, you could literally walk from Papua New guinea across to.

[Unknown]

Australia, across to Tasmania.

[Dan Snow]

And so all that was considered one large sort of landmass because the continental shelf was exposed and all of those areas were much.

[Unknown]

The sea level was lower. And so animals could literally. And people could walk back and forth as needed.

[Larissa Desantis]

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

[Unknown]

Yes. Although again, it's fluctuating. Right. So there's going to be periods where.

[Dan Snow]

You have an interglacial and you can't, you have to, you know, use some other means or those, those pathways are.

[Unknown]

Cut off for whatever species that might be and other periods where they're connected.

[Dan Snow]

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, part isolated, connected, isolated.

[Larissa Desantis]

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?

[Unknown]

Sure, yeah, they're pretty standard and largely.

[Dan Snow]

Caused by sort of orbital cycling. And so the, the Milankovitch cycles contribute to the magnitude at which they occur.

[Unknown]

And also the regularity which they occur.

[Dan Snow]

And typically you have sort of these fluctuations. You have different sort of clocks moving and different sort of patterns that are actually happening. So they tend to be fairly regular.

[Unknown]

Over the long term, but they can be variable.

[Dan Snow]

But you typically go from a period of pronounced glacials and then you start having the warming, the melting of the ice that's going to cause sort of the warming in general of other surrounding areas.

[Unknown]

You have these positive feedback loops that basically lead to expedited warming events which.

[Dan Snow]

Usually happen pretty quickly. And then again, sort of, you'll start.

[Unknown]

To have cooling events that will happen thereon after. So you just kind of go from.

[Dan Snow]

Cycle to cycle between glacial and interglacials.

[Larissa Desantis]

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?

[Dan Snow]

Yes, Sahul, or. I don't know the exact pronunciation, but.

[Unknown]

That'S how I say it with my American accent.

[Larissa Desantis]

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.

[Unknown]

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

[Dan Snow]

A lot of what we have is identified to Pleistocene.

[Unknown]

And so we don't exactly know from.

[Dan Snow]

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.

[Unknown]

Sort of the heyday. In other places like North America, you.

[Dan Snow]

Have lots of megafauna at places like the La Brea Tar Pits and you.

[Unknown]

Have a really good record for the past 50,000 years.

[Dan Snow]

That's well within the time that we can actually radiocarbon 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.

[Unknown]

Others are sort of beyond the limits of radiocarbon dating.

[Dan Snow]

So they're older than 50,000 years.

[Unknown]

So other forms of dating are used.

[Dan Snow]

To try to date sort of the sediments surrounding these fossils. But I'd say a lot of the.

[Unknown]

Material that we know the most about is from the latest Pleistocene.

[Dan Snow]

So somewhere around, you know, 60,000 to 30,000 ish years and there's a variety of sites. Now there's also a lot of material that we've identified to Pleistocene. It could well fall in that area. It might be much older.

[Unknown]

And so it's hard to know exactly.

[Larissa Desantis]

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?

[Dan Snow]

So what essentially happens is with any sort of radiometric dating, you have a.

[Unknown]

Parent product and then what they call the daughter product.

[Dan Snow]

And essentially what happens is you have decay from that parent product to this daughter product.

[Unknown]

And you measure the ratio between these.

[Dan Snow]

And the half life for C14 is.

[Unknown]

Somewhere around 5,000 years.

[Dan Snow]

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

[Unknown]

You know, undergone decay.

[Dan Snow]

And so at the point that you're getting towards that, that 50,000 window, you.

[Unknown]

Have such small amount of material and it's, it's approaching sort of limits of.

[Dan Snow]

The, the machinery, the technology 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 to the last roughly about 50,000 years. 40,000 is probably where we get good dates. Other places in the world we can get really nice chronologies leading up to sort of extinction events. But in Australia it's a bit more challenging. And so other methods are used. The other, you know, a lot of times when you hear about radiometric dating, you know, during the time of the.

[Unknown]

Dinosaurs, that's using volcanic ash layers.

[Dan Snow]

So you have these volcanic events and you're using a different, you're usually Looking.

[Unknown]

At potassium argon dating or a different metric and so different amounts of decay.

[Dan Snow]

That'S happening at different rates and that's giving us some sort of indicator of.

[Unknown]

What time those events are happening.

[Dan Snow]

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.

[Unknown]

Events, especially in the late Pleistocene.

[Larissa Desantis]

Well, it's very commendable for, well, 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. And I'm guessing it's looking at sediments from there and other evidence surviving Larissa to get more of an understanding of was 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?

[Unknown]

Sure.

[Dan Snow]

There was all sorts of amazing animals that. 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.

[Unknown]

See some of the classic ones.

[Dan Snow]

You get to see diprotodons which are.

[Unknown]

Giant wombat like animals the size of rhinos.

[Larissa Desantis]

Giant rhino sized wombats? Wow.

[Dan Snow]

Yes. Or wombat like animals. They're not quite wombats exactly, but they were massive. We don't think of large megafauna. That's scale in places like Australia today.

[Unknown]

You also had giant kangaroos.

[Dan Snow]

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 goannas that you might see in Australia today, imagine them the size of a soul water crocodile.

[Larissa Desantis]

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

[Unknown]

Yes.

[Dan Snow]

So that's, I feel like not as.

[Unknown]

Hard to envision in Australia because we have giant flightless birds there today.

[Dan Snow]

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.

[Unknown]

Shape, a jenny ornis, much more massive.

[Dan Snow]

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.

[Unknown]

And I haven't even mentioned what I think is the coolest, the most interesting and most exciting.

[Dan Snow]

One of my favorites is actually often referred to as the marsupial lion, but.

[Unknown]

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

[Larissa Desantis]

A killer wombat. Amazing.

[Dan Snow]

Killer wombat.

[Unknown]

And it's, it's not totally an unfounded name.

[Dan Snow]

So very similar to how, you know, giant pandas are an herbivorous animal that eats plants that evolved from a carnivorous group.

[Unknown]

Right.

[Dan Snow]

It's, they're a bear.

[Unknown]

They're related to grizzly bears and black bears and polar bears, things that primarily.

[Dan Snow]

Eat meat 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 largest mammalian predator in Australia. And it's always kind of funny because, you know, the, the Australians like to.

[Unknown]

Scare the tourists and talk about these things called drop bears.

[Dan Snow]

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

[Larissa Desantis]

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

[Dan Snow]

Yes, yes, yes.

[Unknown]

But these were sort of like, you.

[Dan Snow]

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.

[Unknown]

They weren't chasing things in like open ecosystems.

[Dan Snow]

They were definitely, you know, using the element of surprise to take down any prey. And in fact, a lot of the.

[Unknown]

Work we've done, and I'm happy to.

[Dan Snow]

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.

[Unknown]

Consuming vegetation in the densest of the forests.

[Dan Snow]

And so they relied on these trees.

[Unknown]

To do their hunting.

[Dan Snow]

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.

[Unknown]

Have the opening up of these landscapes, aridification that's happening, declines in forests.

[Dan Snow]

And these animals, we're finding out, although they could, you know, crunch or eat.

[Unknown]

A variety of different things, they were.

[Dan Snow]

Highly specialized on things that were browsing or eating leaves in forested environments.

[Larissa Desantis]

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, 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 nice areas as well. Was it just as diverse back then? What do we know?

[Dan Snow]

Yeah, so there were some differences, right? There are some areas that actually today.

[Unknown]

Are named, you know, Nullarbor, which means.

[Dan Snow]

No tree, but there's evidence of, of.

[Unknown]

Animals living there that would have required forested ecosystem.

[Dan Snow]

So what we do know is that they likely experience 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, the monsoon, the strength of the.

[Unknown]

Monsoon is sort of weakened over time.

[Dan Snow]

And this has led to widespread aridification or the drying out of the continent. And I think often people sort of underestimate the role that extreme heat and drought can play on an ecosystem. 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.

[Unknown]

And that's largely affecting kind of their distribution today.

[Dan Snow]

At the time, you know, there a lot of things were bigger, right? So you had, you know, we talked about the diproted on the giant wombat.

[Unknown]

Like animal the size of a rhino.

[Dan Snow]

But you had several different types of those.

[Unknown]

You had another one called Zygomaturus and.

[Dan Snow]

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.

[Unknown]

And so you had lots of these large animals. You had quite a diversity of different types of kangaroos, some kangaroos that were.

[Dan Snow]

Eating different types of vegetation that I'll talk a little bit more about. But is difficult, a type of vegetation.

[Unknown]

That'S difficult to eat today, primarily because.

[Dan Snow]

It has lots of salt. There's 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.

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[Larissa Desantis]

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

[Unknown]

Koalas used to be much more diverse.

[Dan Snow]

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.

[Unknown]

Miocene, which is an older time period.

[Dan Snow]

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

[Unknown]

Had this enormous diversity and that diversity has largely been cut short with these.

[Dan Snow]

Various extinctions or even just how environments have changed over time.

[Unknown]

Australia is a story about aridification, so.

[Dan Snow]

We often will zoom into the Pleistocene.

[Unknown]

And look at the short term impacts of a ratification.

[Dan Snow]

And and honestly that's what drew me to working in Australia. I worked in Florida looking at effects of glacial and interglacial periods and I really wanted to know what happens when an environment is really stressed to the max, right when you have extreme aridification, and that's Australia. But Australia has also undergone aridification over millions of years. 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 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. There were things related to diprotodons kind of from that sort of group that.

[Unknown]

Were up in the trees, kind of.

[Dan Snow]

Like 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.

[Unknown]

Out and this is something that's happening.

[Dan Snow]

Sort of also globally. You know, one of the, the big events is, you know, Australia, Antarctica and.

[Unknown]

South America were all connected at one point. And you have the unzipping of these continents.

[Dan Snow]

And ultimately when you isolate not just Australia and South America, but also Antarctica and you begin to have ocean circulation that's just circulating around Antarctica. You have that cold water that sort of allowing for these cold environments and therefore the buildup of glaciers and ice and that's actually contributing to sort of global cooling.

[Unknown]

Right. Before that sort of water was sort.

[Dan Snow]

Of directed up into other areas, you would have warm water making it into these, these cooler areas. And much like, you know, today you.

[Unknown]

Can have palm trees in some parts of England, right. Because of the Gulf Stream coast, you.

[Dan Snow]

Had other sort of phenomenon that were.

[Unknown]

Keeping parts of these areas very warm. And when you have this separation, we.

[Dan Snow]

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.

[Unknown]

More open woodland environments as opposed to the rainforest that had sort of predominated previously.

[Dan Snow]

And we often refer to this shift.

[Unknown]

As kind of going from like the.

[Dan Snow]

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. And I think part of the reason you get such iconic and unique animals is largely because these animals evolved in.

[Unknown]

Isolation for such a long period of time.

[Larissa Desantis]

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

[Unknown]

There were.

[Dan Snow]

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.

[Unknown]

Not quite as big or not nearly.

[Dan Snow]

As big as, you know, the, the titanoboa, which is a. A paleocene or aged snake that's from South America. You know, that's when it was really warm and these snakes could get really, really large.

[Unknown]

But it is a pretty massive snake.

[Dan Snow]

You know, for the time especially, and is found in a few sites in.

[Unknown]

In the southern part of Australia.

[Dan Snow]

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.

[Unknown]

They're the ones that are usually not venomous.

[Dan Snow]

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

[Larissa Desantis]

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 from 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?

[Unknown]

Yes and no. There are a fair number of sites.

[Dan Snow]

In Australia that preserve megafauna, but there are far fewer that demonstrate coexistence of humans and megafauna.

[Unknown]

And so.

[Dan Snow]

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.

[Unknown]

We tend to see if we do.

[Dan Snow]

Have evidence of any butchering or killing. It's actually usually of things that have.

[Unknown]

Actually survived into the present.

[Dan Snow]

Things like, you know, the redneck wallaby or whatnot, which are quokkas, for example, that are or were consumed until recently. And so it's quite interesting. There's, you know, the smoking gun of seeing, you know, these butchered sites with, you know, human artifacts and megafauna remains.

[Unknown]

Remains to be seen or found.

[Dan Snow]

And I think that's really caused a lot of question about what the causal.

[Unknown]

Factors are to the extinction.

[Dan Snow]

And, and we've.

[Unknown]

We've talked about some of the different.

[Dan Snow]

Animals and, and I think, you know, a lot of what.

[Unknown]

What I do and what other researchers.

[Dan Snow]

In the area are doing is trying to understand their paleoecology and paleobiology. So before we even get to sort.

[Unknown]

Of what killed them off, how did.

[Dan Snow]

They Live 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.

[Unknown]

Of feature one animal.

[Dan Snow]

So there's this one animal called Procoptodon goliath and it's a short faced.

[Larissa Desantis]

Sorry, what was that?

[Dan Snow]

Goliath.

[Unknown]

And it's a short faced kangaroo.

[Dan Snow]

A goliath, right. It's a giant short faced kangaroo. And interestingly when people started studying this animal, it has a lot of morphological.

[Unknown]

Features or the shapes of its bones.

[Dan Snow]

Indicate that it was probably eating browse, which are things like leaves in contrast to grass, which, which is pretty self evident. And so when, when researchers started actually kind of looking at the isotopic signature.

[Unknown]

So this is a way to get.

[Dan Snow]

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.

[Unknown]

And that's one approximation.

[Dan Snow]

If people did an approximation of, of our diets, we would be omnivores.

[Unknown]

We are the classic omnivores.

[Dan Snow]

We have teeth that are ideal for, you know, crushing and grinding. We're not hyper carnivorous, we're not obligate.

[Unknown]

Herbivores, we're not just eating plants.

[Dan Snow]

Now that being said, right, I might eat lots of sushi and someone else might eat, you know, lots of steak.

[Unknown]

And someone else might be vegan.

[Dan Snow]

And those are all, you know, variation.

[Unknown]

And you do have variation within natural populations as well.

[Dan Snow]

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.

[Unknown]

Eating a C4 plant or a C3 plant.

[Dan Snow]

And those are plants that photosynthesize a little bit differently.

[Unknown]

And then we can look at the.

[Dan Snow]

Microar and say, oh, they were eating.

[Unknown]

Shrubs, not grass or they were eating grass, not shrubs.

[Dan Snow]

And in Australia things get really complicated.

[Unknown]

Really quickly because there's such a diversity of vegetation.

[Dan Snow]

And you know, when I work in places like Florida or you know, colleagues.

[Unknown]

Who of mine who work in places.

[Dan Snow]

Like East Africa, it's a very simple system. You have essentially C4 grasses, so the grass. So when you get a C4 signal, that means the animal's eating grass and.

[Unknown]

You have C3 plants.

[Dan Snow]

But in Australia we have C3 grasses and C4 grasses.

[Unknown]

We have C3 plants and C or.

[Dan Snow]

C3 shrubs and C4 shrubs. And so you can't really see anything.

[Unknown]

Unless you're both looking at the isotopes and looking at the microware. And you're probably at this point saying.

[Dan Snow]

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.

[Unknown]

Also tell us about the vulnerability of that animal to that environment.

[Dan Snow]

So in the case of Perofton Goliah, we end up finding that they are eating C4 shrubs.

[Unknown]

And this is based on both the.

[Dan Snow]

Microware and the isotopes.

[Unknown]

What that tells us is that they're consuming saltbush, right?

[Dan Snow]

They're consuming a lot of this, this, this species called, or this from the genus Atroplex. And as the name or the common.

[Unknown]

Name implies, saltbush has salt.

[Dan Snow]

And so if you're out hiking all day and you've got a bag of.

[Unknown]

Potato chips and you've got an apple.

[Dan Snow]

In your bag, right, which one are.

[Unknown]

You going to go for if you.

[Dan Snow]

Haven'T had water in the last few hours?

[Larissa Desantis]

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

[Unknown]

Exactly.

[Dan Snow]

And so if you're going to consume this resource which is prevalent in large parts of Australia, that's great.

[Unknown]

That's a resource that these animals can explore and niche that they can sort of occupy. But it also requires that they are consuming water.

[Dan Snow]

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.

[Unknown]

Also incorporated into your tissues.

[Dan Snow]

And so we can actually see that.

[Unknown]

Peropton Goliath, compared to other co occurring.

[Dan Snow]

Kangaroos has much lower oxygen isotope values, indicating that it's drinking water.

[Unknown]

It's not just getting water from plants that it's eating. What this tells us is you have.

[Dan Snow]

This giant C4 browser that's eating saltbush predominantly on the landscape. It's going to require water and it's going to require water at regular intervals. As the environment starts to dry out and you have increased aridification, it's going to make this animal more vulnerable to extinction. The fact that this animal is also large makes it more vulnerable to extinction. Because what we know about larger animals.

[Unknown]

Is they typically produce fewer offspring.

[Dan Snow]

And so anything that has a smaller in number and occupies more space is more likely. The possibility of getting to zero through various stochastic or random processes is more likely the smaller that number is so these are all things that make it vulnerable. Also, if it's going to watering holes.

[Unknown]

It'S more vulnerable to predation. And that predation could be humans. It could be humans predating on them.

[Dan Snow]

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.

[Unknown]

Or the less observant prey animal that comes up to the water and doesn't.

[Dan Snow]

See the crocodiles there.

[Larissa Desantis]

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

[Dan Snow]

Yes, absolutely. And so it makes Rahabta and Goliath incredibly vulnerable if water sources are becoming fewer and far between or if the risk at these water sources is increasing in any way. And so what do we see? We see them go extinct and this gives us 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.

[Larissa Desantis]

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 extinctions.

[Dan Snow]

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.

[Unknown]

Can reproduce and invest their energy and there's constantly trade offs.

[Dan Snow]

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.

[Unknown]

Those surviving is going to be lower.

[Dan Snow]

So some classic examples of this are if you think of, you know, fish, right? So fish have tons and tons of eggs. What's the chance that, you know, any one of them is going to survive.

[Unknown]

Is pretty low, but they have so.

[Dan Snow]

Many that it's sort of A numbers game, right? Inevitably, likely some will survive.

[Unknown]

Alternatively, you have things on the, you.

[Dan Snow]

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.

[Unknown]

In that one offspring. There's a lot of investment both in.

[Dan Snow]

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.

[Unknown]

Lot of time and resources and parental.

[Dan Snow]

Care after it's born. And humans are, you know, obviously one.

[Unknown]

Of the most extreme, right?

[Dan Snow]

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 a slightly younger age, there's.

[Unknown]

Still a lot of parental care that's being invested.

[Dan Snow]

And so when you have things that can reproduce quickly, things like rodents, rabbits.

[Unknown]

They produce lots of offspring at one time. Some of them can reproduce multiple times a year. Those things are able to sort of respond, it's sort of a numbers game to any stochastic processes, right?

[Dan Snow]

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 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.

[Unknown]

Down to zero, if you hit zero, that's it.

[Dan Snow]

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, it's really a numbers game. And unfortunately, the things that are the biggest in many cases today at least.

[Unknown]

Are the things that are most vulnerable to going extinct.

[Larissa Desantis]

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 and 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?

[Dan Snow]

Yeah, so we, the idea used to be, and I'm going to kind of.

[Unknown]

Give you a little bit of the.

[Dan Snow]

History because it Explains it gets into.

[Unknown]

The extinction debate a little bit. But the idea used to be that.

[Dan Snow]

They thought people came over roughly about 45,000 years ago, and they also thought that a lot of the megafauna were.

[Unknown]

Going extinct around this time.

[Dan Snow]

And so there was this sort of.

[Unknown]

Reigning hypothesis called the blitzkrieg hypothesis.

[Dan Snow]

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 things that we've.

[Unknown]

Learned is actually people came over much earlier.

[Dan Snow]

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.

[Unknown]

We have some sites that show coexistence.

[Dan Snow]

Of humans and megafauna, which is really exciting.

[Unknown]

So there's a site called Lake Mongo.

[Dan Snow]

And also a site that I worked.

[Unknown]

Quite extensively with, which is called Cuddy Springs.

[Dan Snow]

And this was a site.

[Larissa Desantis]

Ah, Cuddy Springs, yes, yes.

[Dan Snow]

And Cuddy Springs is an inch. So when I first, my first trip to Australia, you know, I went over there really interested in looking at sort of extreme responses to climate change. And I had no idea that, you.

[Unknown]

Know, Cuddy Springs at the time was as controversial as it was.

[Dan Snow]

And one of the reasons it was.

[Unknown]

So controversial, and I say was because.

[Dan Snow]

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.

[Unknown]

And this idea, just the existence of.

[Dan Snow]

Cuddy Springs showing coexistence of megafauna at some time after this 40, 45,000 year interval went against this blitzkrieg hypothesis. And so it received a lot of what I think is 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.

[Unknown]

A, it's a mixed assemblage.

[Dan Snow]

And, and the woman who has done so much for the site is Jude Field, she's an archaeologist. She excavated the site for decades and worked with first nations people to learn.

[Unknown]

About the history of the site and.

[Dan Snow]

To excavate it with them as well. And, and really did a lot of remarkable work. But you Know, anytime there was sort of a contentious issue, she would go out and find the best person to help, sort of test that question. And so, for example, when they said.

[Unknown]

Oh, it's a mixed assemblage, everything's jumbled together.

[Dan Snow]

Well, let's test that.

[Unknown]

So she reaches out to Clive Truman.

[Dan Snow]

Who'S an expert on rare earths. And they used rare earths, which is.

[Unknown]

A kind of a way of looking.

[Dan Snow]

At different chemical signatures and in fact shows. No, we have these sort of intact assemblages. And just for a long time, I.

[Unknown]

Think just cuddy springs being cuddy springs.

[Dan Snow]

And I'm sure there was, you know, the fact that you had a female.

[Unknown]

Archaeologist leading a lot of this work.

[Dan Snow]

And contrasting what a lot of the, you know, typically male archaeologists were saying at the time.

[Unknown]

I'm sure that played into it as.

[Dan Snow]

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 kangaroos eating? What are, you know, we have these ideas based on their morphology, but what.

[Unknown]

Is their diet and what can we.

[Dan Snow]

Tell about these animals? 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.

[Unknown]

And so what we did is we actually looked at all of the animals.

[Dan Snow]

That were in both of those different horizons and had been carefully excavated.

[Unknown]

And I will say, being a paleontologist.

[Dan Snow]

And knowing archeologists, archaeologists do a far better job of excavating fossil localities.

[Unknown]

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

[Dan Snow]

This often is now occurring in paleontological.

[Unknown]

Sites, but still not to the rigor.

[Dan Snow]

And the level that archaeologists do it. But everything had been meticulously excavated. We knew the horizons that they were.

[Unknown]

In, that rare earths had been done. When we looked at the isotopes, what.

[Dan Snow]

We found was pretty astounding, is that.

[Unknown]

The kangaroos, we know, kangaroos are actually.

[Dan Snow]

Really good at telling us something about climate.

[Unknown]

And we know that based on modern kangaroos today. So you can look at kangaroos from.

[Dan Snow]

Really wet environments, really dry environments and sort of in between, and you can actually use those oxygen isotopes to reconstruct the environment.

[Unknown]

And we can do that with modern ones.

[Dan Snow]

So we know where these kangaroos are from. We know that they live in high rainfall areas or low rainfall areas.

[Unknown]

We look at the auction isotopes and.

[Dan Snow]

We see this beautiful map where we can say, okay, these are from drier areas, these are from wetter areas.

[Unknown]

And once we sort of have tested that to make sure it works in.

[Dan Snow]

The modern, we can take that back.

[Unknown]

Into the fossil record.

[Dan Snow]

And so we, when we do that.

[Unknown]

At Cuddy Springs, we see that you're.

[Dan Snow]

Going from a fairly dry environment, but to a drier environment.

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[Larissa Desantis]

So we Cuddy 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, 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.

[Dan Snow]

Yes, absolutely.

[Unknown]

So as you're kind of comparing the.

[Dan Snow]

Different layers, we can see this sort of shift in the oxygen isotope.

[Unknown]

So it's not going from wet to.

[Dan Snow]

Dry, you're going from dry to drier. And with that we can also look at what the animals are eating.

[Unknown]

So the oxygen tells us about what.

[Dan Snow]

They'Re, how, what the water is like or what the climate is like.

[Unknown]

And the carbon isotopes can tell us.

[Dan Snow]

What exactly they were eating. Were they eating C3 plants or C4 plants? And then we can look at the microwear which can tell us was it.

[Unknown]

Shrubs, was it grass? And so when we begin to map.

[Dan Snow]

This out, what we find is that.

[Unknown]

With increased aridification, so as things are.

[Dan Snow]

Getting drier, which we can see with the kangaroos. Right.

[Unknown]

So the kangaroos are also demonstrating this at the site.

[Dan Snow]

We also see a shift away from eating C4 resources.

[Unknown]

And this is actually in contrast to.

[Dan Snow]

What I see in Florida happening during glacial interglacial time. When you go from 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 mammoths and all.

[Unknown]

Sorts of things that are able to eat the C4 resources. You have other things that are browsing.

[Dan Snow]

You actually have two different types of.

[Unknown]

Camels that exist because one can do one thing and one can do the other.

[Dan Snow]

And so it's sort of this more resources in the landscape. What's interesting about Australia is that these animals stop eating these C4 resources.

[Unknown]

And this got us thinking, okay, well.

[Dan Snow]

What are these C4 resources? Well, it turns out similar to Procopton.

[Unknown]

Goliath, the short faced kangaroo, many of these C4 resources are things like saltbush.

[Dan Snow]

And so we don't know if the saltbush has gone away. In fact, we don't think it has. We think it's probably stayed on the landscape.

[Unknown]

But what we do are learning is.

[Dan Snow]

That these animals are likely unable to.

[Unknown]

Eat those resources, eat that C4 saltbush anymore.

[Dan Snow]

So they're having to sort of not eat that food and now having to compete for more similar resources. So with the drying out of the continent that's happening sort of, you know.

[Unknown]

Globally, but also locally, the Lake Erie Basin is drying out, you have the weakening of the monsoon signal, for example.

[Dan Snow]

You'Re seeing this shift in the kangaroos that's being recorded via climate, but you're.

[Unknown]

Also seeing sort of a dietary shift.

[Dan Snow]

Away from certain resources. 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.

[Unknown]

What the impacts are of aridification.

[Dan Snow]

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?

[Unknown]

Like this doesn't seem earth shattering or groundbreaking.

[Dan Snow]

You know, the animals are vulnerable to climate change. Said, yeah, but when we published that.

[Unknown]

Paper, the paper took us a while to get out.

[Dan Snow]

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 up 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 January of 2017, January 20th of 2017, papers from Nature Communications.

[Unknown]

Said humans rather than climate, the primary cause of Pleistocene megafaunal extinctions in Australia.

[Dan Snow]

Then our paper came out about a week later and said, didn't say anything.

[Unknown]

About causal factors, but said dietary responses.

[Dan Snow]

Of Sahul, Pleistocene Australia, New guinea megafauna to climate, 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.

[Unknown]

Saying at least 17,000 years of coexistence.

[Dan Snow]

Between modern humans and megafauna.

[Unknown]

And this is from the Lake Mungo.

[Dan Snow]

Wallandra Lakes site that was led in the, in the paper that was led by Michael Westaway. But essentially they demonstrated another site that showed an animal called Zygomaturus and megafauna.

[Unknown]

Coexisting for some period of time. So now it's not just Cuddy Springs.

[Dan Snow]

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.

[Unknown]

Of 2017, a paper came out in Nature saying human occupation of northern Australia.

[Dan Snow]

By 65,000 years ago. And so we're starting to see this sort of more complete picture of what's.

[Unknown]

Sort of happening, in which case there.

[Dan Snow]

Might be more prolonged coexistence of humans.

[Unknown]

A variety of causal factors.

[Dan Snow]

But I think it just goes to.

[Unknown]

Show the importance of actually kind of.

[Dan Snow]

Stepping back and trying to understand just even the paleobiology of these animals, what they're doing, before we jump on any one theory and to try to argue, you know, why these were going extinct.

[Larissa Desantis]

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. Yeah, it's, 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?

[Dan Snow]

Yes, yes. Related to Diprotodon, it's maybe more of a forested dweller. There's some different hypotheses there, but yes, it's a. Maybe think of a smaller rhino size or a large taper size, but still quite large.

[Larissa Desantis]

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. 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?

[Unknown]

Yeah, I think that's a great question. I think what we really have to do is look at the evidence.

[Dan Snow]

I am a scientist, I look at data and I try not to, I'm sure I have my own biases, but I try not to, to be open.

[Unknown]

Minded when new data come about. So, for example, and I'm going to.

[Dan Snow]

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 there the data look as if the megafauna at La Brea at least.

[Unknown]

Are going extinct locally right about the.

[Dan Snow]

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 how better to explain it. It's literally just jumping in magnitude.

[Unknown]

And so there.

[Dan Snow]

We don't know, we don't know. Was it humans who are lighting these fires?

[Unknown]

Presumably this is at the same time.

[Dan Snow]

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.

[Unknown]

The humans very well may have played.

[Dan Snow]

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 the compelling. And so there's no like clear evidence. There's only a few sites that show coexistence.

[Unknown]

And it is possible, of course.

[Dan Snow]

And I think, but I think what's happening is the reigning hypothesis for so long has been one of humans coming onto the continent, killing off everything very quickly. And then iterations of that hypothesis just keep getting stretched thinner and thinner and thinner. I think it's important if we look.

[Unknown]

At all the factors. My students will often ask me, why does it matter?

[Dan Snow]

Why does it matter if it's climate change or if it's humans that are contributing to the extinction. This is what I tell them.

[Unknown]

Presumably if it is just humans, if human over hunting was the cause of megafauna of these megafaunal extinctions, then if we stop hunting these animals then presumably.

[Dan Snow]

Everything will be fine, right?

[Unknown]

That these animals would be able to.

[Dan Snow]

Respond positively and you remove that factor.

[Unknown]

But if climate change played any role.

[Dan Snow]

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.

[Unknown]

If climate change did play a role in the past, that's really important to know and to be able to learn.

[Dan Snow]

And disentangle, especially if we need to think about that and how we would.

[Unknown]

Manage for ecosystems moving forward.

[Dan Snow]

And the more and more I, you know, I investigate these different animals, whether it's the, you know, giant short faced kangaroo that was eating C4 shrubs and, and eating to, and 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, you know, just from things from forests.

[Unknown]

And so we know that based on the isotopes and we've looked at the.

[Dan Snow]

Microware of these, they have, you know.

[Unknown]

Bolt cutters for teeth, they could eat whatever they wanted, but they are only.

[Dan Snow]

Eating things actually within these dense forests.

[Unknown]

And so what that tells me is.

[Dan Snow]

That when environments are getting drier and opening up and fewer forests, that these animals are losing the upper hand that.

[Unknown]

They have, which is being able to.

[Dan Snow]

Ambush, hunt from trees potentially or eating these forest browsers.

[Unknown]

These forest browsers are also disappearing from these ecosystems.

[Dan Snow]

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 cons, you know.

[Unknown]

Continue to evaluate all of the different.

[Dan Snow]

Hypotheses and to, you know, on that note, I remain open about looking at the impacts of humans. I just don't want to prematurely assume it was humans when we don't necessarily have clear evidence that it was. And I also think it's important. So I'm not an archeologist, I think, oh, I should, I should make that clear.

[Unknown]

I'm a paleontologist.

[Dan Snow]

But in Australia a lot of the sites are, you know, most of the sites are paleontological and a few have archaeological remains. But paleontologists and archaeologists work together all the time. 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 kind of working within a much more recent timeframe. 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.

[Unknown]

Wildlife management than we do.

[Dan Snow]

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.

[Unknown]

A few of the things that, that.

[Dan Snow]

I've become aware of or learned about are things like totems and how different individuals within different groups would be, you know, sort of assigned a totem or an animal that they were responsible for. And this was an animal that they.

[Unknown]

Would not consume, but it was an animal that they also would.

[Dan Snow]

Would try to manage. Right. And they would. They would be knowledgeable about if the.

[Unknown]

Population was increasing or decreasing.

[Dan Snow]

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.

[Unknown]

That is being done actively by archaeologists in this area, also by paleontologists.

[Dan Snow]

But there's. There's a lot that I think I, you know, we don't fully understand with sort of how people were managing or respecting their environment. And also we need to kind of consider those factors.

[Unknown]

We can't just take the sort of.

[Dan Snow]

Western view of conquering, bring it to Australia and say, therefore, megafauna went extinct. We need to kind of step back, really evaluate and be open to other hypotheses.

[Larissa Desantis]

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. The Desantis Dream Lab, what it is and why it's important and linked to your research.

[Unknown]

Sure.

[Dan Snow]

So our lab is the Dream Lab.

[Unknown]

Which stands for Dietary Reconstructions and Ecological Assessments of mammals, which is a bit.

[Dan Snow]

Of a mouthful, but what we're trying to do is really understand how mammals.

[Unknown]

Have responded to climate change in the past. There's actually an entirely new field that developed within the past few decades, which.

[Dan Snow]

Is referred to as Conservation paleobiology, much.

[Unknown]

Like conservation biology, we ask questions that.

[Dan Snow]

Are of relevance to conservationists, but we actually use the fossil record to ask and answer those questions. We try to look at which animals.

[Unknown]

Responded to these climate changes or what were the impacts of these extinctions.

[Dan Snow]

Extinctions.

[Unknown]

And a lot of the questions that.

[Dan Snow]

We'Ve been trying to look at is not just why did animals go extinct.

[Unknown]

But what were the subsequent consequences of.

[Dan Snow]

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. And the western part of North America.

[Unknown]

For example, experiencing all of these fires.

[Dan Snow]

This is very similar to what happens.

[Unknown]

In Australia as well in these different sort of Mediterranean climates.

[Dan Snow]

So in some ways we're trying to use what we can from the past to extract important sort of conservation lessons and even cautionary lessons that can be of relevance to today. And so, you know, I have the privilege of being able to do this on most continents. I primarily work in North America and in Australia, although I have colleagues and collaborations on all continents except for Antarctica.

[Larissa Desantis]

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

[Dan Snow]

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

[Larissa Desantis]

Well, there you go.

[Tristan Hughes]

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 favorite favor. 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 [e-mail] subscribe.

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[Dan Snow]

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This, this Also start with the topics. Hot.

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[Larissa Desantis]

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[Dan Snow]

Com.