American Extinction Part 1: Climate Conundrum

Nowhere is more central to the subject of the Late Pleistocene extinctions than the Americas. It was based on the staggering losses of megafauna here that an American geoscientist, Paul Martin, proposed his theory that the first humans to enter the New World were responsible for the elimination of most large-bodied species through overhunting, also known as “overkill”¹.

His idea has been strongly contested of course, with others arguing that it was instead climate change which doomed the animals² or at least contributed in a substantial way alongside humans^{3 4}. Others yet argue for the importance of indirect effects of human activity on ecosystems^{5 6 7} , while a few promote unsupported theories like a comet impact or hyper-disease^{8 9} . The debate has continued for decades and it is unlikely a consensus will be reached any time soon.

This series will be divided into two parts. This is the first, wherein I meticulously discuss the inadequacy of climatic explanations for the extinctions, and then lay out why a primarily human causation makes more sense. The sequel will delve into what we know about human arrival, the evidence for human predation on megafauna, and examine the details of how extinctions may have unfolded as people spread through the New World.

Fair warning, this post is quite lengthy, so references will be hidden behind a spoiler tag for easier scrolling.

Before we get started, we need to set up more context first.

Background and Challenges

Towards the very end of the Pleistocene, the large majority of North and South American megafaunal genera-72% in North America and 83% in South America-went extinct¹⁰. The extinctions in the Americas have a lot in common with those in Australia, another focal point in the debate about overkill. In both cases, megafauna with no prior exposure to hominins went extinct soon after human arrival. In both cases, the typical suspects are climate and humans. There are important differences, however.

1. The extinctions in the Americas were far more recent, resulting in a far better fossil record with more remains and better dating on those remains. This makes pinpointing when various megafauna disappeared easier, although not without difficulty.
2. Whereas in Australia, there is only one site alleged to indicate a much earlier date for human entry than traditional estimates, in North and South America there are many. This has made it hard to determine precisely when humans arrived in the Americas.
3. While claims about major climate change during the extinction window in Australia are controversial, there is no disputing that a dramatic shift was taking place when American megafauna died off.
4. In Australia, there is no agreed-upon direct evidence for human predation on megafauna, such as kill sites, unlike in the Americas where there is plenty.

In my post on Late Quaternary Australian extinctions, I showed that narrowing down the timeframe for extinction and refuting claims about concurrent climate change are enough to attribute responsibility to humans. In the Americas by contrast, the undeniable climate shifts coinciding with human settlement complicate causation. The presence of climate change does not rule out a primarily human-driven extinction, nor does evidence of human predation negate a climatic role. Assuming both contributed roughly equally, on the other hand, risks falling into the middle-ground fallacy. A different approach is needed.

Making matters more complex is the debate over whether humans drove extinction through simple overhunting of each species(classic overkill), trophic disruption⁷, or whether the human use of fire and/or selective elimination of keystone species drastically altered environments leading to further extinctions^{5 6} . For the sake of simplicity, I will use “environmental change” here to refer to the kinds of broad biome changes primarily brought on by natural forces like climate, and then address the finer details of human impact in the next part.

Timing is another issue. Some claim humans reached the Americas south of the ice sheets well before the usually accepted 16-14 kya timeframe^{11 12}, while others claim extinct megafauna survived on the mainland into the Holocene¹³. Both are used to challenge overkill or at least its rapid (blitzkrieg) version^{13 14}. However, these claims remain controversial. I have addressed the early human arrival claims before and will do so again part 2.

Studies often claim evidence of megafauna surviving on the American mainland after 10,000 years before present, but many are inconclusive or dubious. Often, they rely on sedimentary DNA detected in soil samples¹⁵, but dating these sediments is problematic due to reworking, which can yield erroneously young survival dates¹⁶. Late dates from directly testing fossils are also usually based on flawed methods and tend to be refuted upon retesting¹³.

While such findings are understandably exciting for researchers and science enthusiasts, it is best to exercise the same caution and scrutiny towards them as with anything else in science. Further, regardless of when humans first set foot in the Americas or when the last members of extinct species died off, we have enough evidence to say that an abrupt collapse of megafaunal populations took place during the glacial-interglacial transition^{17 18}.

We will start by looking at the patterns surrounding this collapse, and see whether climate fits as the central cause.

Unprecedented Losses

At first glance, climate change seems like a compelling explanation for the extinctions in the Americas. These losses occurred during significant global climate shifts as the ice age ended. The massive North American ice sheet melted rapidly, pushing cold-adapted plants and animals northward.

While dramatic, the environmental transformations during this period were not unprecedented. Similar glacial-interglacial transitions had occurred over hundreds of thousands of years without causing megafaunal losses on this scale^{6 19}. The survival of past animal communities through these cycles is an enduring objection to climate-based explanations.

Moreover, the sheer number of extinctions does not fully capture how anomalous this event was-details about which groups disappeared are quite telling. Certain taxa had thrived in the New World for millions of years: proboscideans for 16 million, ground sloths for 35 million, glyptodonts for 38 million, litopterns for 62 million, and horses for 56 million. Yet, not a single species from these groups survived. Most vanished by the early Holocene, with a few lingering on islands until the mid-Holocene^{20 21} .

The abrupt loss of such long-established taxa in a geologic instant is so unprecedented in Quaternary history that it requires a better explanation than standard climate cycles alone.

Uneven Climate Change

Comparisons across continents are just as important as comparisons across time. But continents have experienced varying durations of anatomically modern human (Homo sapiens) and hominin occupation, as well as distinct climate cycles, so this must be done carefully to minimize confounding variables. Therefore, this post will extensively compare and contrast North and South America.

Why? Both continents were settled by the same group of people, known as Paleo-Indians, around the same time, with no prior hominin presence^{18 22}. However, the way each experienced climate change differed significantly due to different geographical realities. While North America often dominates discussions on extinction, South America provides crucial context for understanding the respective roles of human activity and climate change across both regions.

South America is less climatically turbulent than the mid-upper latitudes of North America^{23 24}. It has a favorable geographic location with most of it being located in the relatively stable southern hemisphere and the part that extends into the northern hemisphere still falling well within the tropics. Glaciations were relatively minor in South America, being restricted to the Andes. In this regard at least, South America is more comparable to Africa or Australia than North America.

Temperature differences between the Last Glacial Maximum and present day were less pronounced in South America than North America²⁵. Environmental changes during the transition to the Holocene largely reflect this pattern. In parts of North America, profound changes took place: areas that were once covered in glaciers were claimed by frigid tundra, then boreal forest, and eventually temperate forest²⁶, but in South America the changes in biomes took place more along a gradient of openness than temperature²⁷.

Warm-climate vegetation zones would have certainly expanded slightly poleward in South America, but the main environmental shift was forested biomes encroaching on grassier ones. However, despite a reduction in area, grasslands and savannahs persisted through the transition and are still present today as vast ecosystems like the Cerrado, Llanos, Beni savannah, Pampas, and others.

All of these details are crucial because, despite South America’s relatively modest climate and environmental changes compared to North America, its megafauna experienced even more severe extinctions¹⁰. The implications of the mismatch between the magnitude of megafaunal loss and climate shifts in South America are often ignored by climate theorists.

With that in mind, let us zoom in to see the issues with climate scenarios for each continent.

Environmental Changes in North America

In North America, there were a myriad of species with wide distributions and varied diets who happened to go extinct. Their fates present a major challenge for climate theories, as one would expect environmental stress to be less harsh on generalists. Arctodus simus, or the giant short-faced bear, is a prime example, ranging from the Pacific to the Atlantic and from central Mexico to (periodically) northern Alaska. Naturally for such a widespread species, it would have survived on a plethora of different food sources and lived in various habitats from tundra to subtropical forest.

Other megafauna, like Megalonyx (Jefferson’s ground sloth), mastodons, and Camelops (a camel), had similar ranges, reaching as far south as Mexico and Central America and-during interglacials-as far north as Alaska and the Yukon. Naturally, their diets varied—what mastodons and Megalonyx in the Cypress swamps of Florida ate differed from what their counterparts in the Canadian taiga ate. Even animals that did not extend that far north, like Smilodon fatalis, dire wolves, and Columbian mammoths, were still highly adaptable and widespread.

This is only a small selection of flexible, broad-ranging species that went extinct, which raises a crucial question: What was so unique about the last glacial-interglacial transition that caused them to disappear completely? The Younger Dryas stadial, a sudden cold snap following the Bølling-Allerød warming, is often cited as a cause¹⁹. While it may have impacted temperate and warm-adapted species, YD-like events were an intrinsic part of climate cycles for hundreds of thousands of years^{28 29}.

The Younger Dryas affected more than just North America—Europe saw even greater climate shifts due to its position downwind of the Atlantic³⁰. Yet, temperate species there like red deer, wild boar, ibex, aurochs, and wisent survived the Younger Dryas. In fact, the European animals that did go extinct during the transition were primarily cold-adapted ones that relied on the disappearing mammoth steppe. This contrasts sharply with North America, where losses were amongst primarily temperate and warm-adapted species living in a variety of habitats.

Further, the distribution of vegetation, perhaps moreso than climate, shapes faunal distribution as animals rely on vegetation for food and habitat. The movement of vegetation zones can lag climatic shifts for millennia, and while deglaciation began around 15–14 kya, North America’s biome map did not fully resemble its modern form until 7–6 kya²⁶. This is very significant-the megafaunal collapse in North America occurred 13-11 kya and was abrupt¹⁸.

A lot of special attention has been given to Beringia, which was situated northwest of the ice sheets and included part of the mammoth steppe^{31 32}. The grazers of this region(woolly mammoth, horse) appear to have declined when warming associated with the Bølling–Allerød promoted shrubby tundra at the expense of steppe-tundra³². While I do not think it is likely that environmental changes alone doomed these animals (as they survived previous interglacials), it should be noted that Beringia is a complete outlier in terms of its environmental history.

Beringia is situated at high-latitudes, and there is no far northern equivalent of the vast stable grasslands that persist into interglacials as seen in mid-latitude North America like the Great Plains, so it is not surprising that grazers living there would struggle to cope with the expansion of shrub tundra and eventually forest. However, it should be understood that this dynamic is not applicable to all of North America.

Environmental Changes in South America

As stated earlier, the mismatch between climate change magnitude and extinction rate in South America remains a serious challenge for climate theorists. However, some have attempted environmental explanations for extinctions in South America anyway, although they do include a role for humans to make it more compelling. According to the so-called “broken zig-zag” hypothesis, closed environments like rainforest expanded greatly in place of the savannah and grasslands that most megafauna relied on³³. The increasingly small and fragmented patches of open areas then made them vulnerable to human hunters.

Addressing this argument is slightly complicated. In North America, this logic would not hold up as we know of iconic megafauna like mastodons and Megalonyx who inhabited closed forests^{34 35} but died off anyway. In South America, however, there is uncertainty about which megafaunal species inhabited tropical rainforests³⁶. This is due to very poor preservation of fossils in such environments and ongoing debates about the Amazon’s extent during glacials.

However, there are important considerations. In nearby Costa Rica, Cuvieronius hyodon clearly dwelled in closed forests and fed on C3 vegetation³⁷. Although it is unclear whether these were true rainforests or more seasonal forests, it should be noted that there is a diversity of forest types in Central and South America and extinct megafauna clearly lived in at least some of them. Second, large herbivores inhabit rainforests in Africa and Asia today, making it hard to imagine that exceptionally biodiverse South American rainforests³⁸ did not host extinct megafauna.

But what can we say about actual rainforest extent during the extinction period? According to Prates and Perez (2021), megafaunal populations crashed abruptly between 12.9 and 10.9 kya³⁹, from the terminal Pleistocene to the very early Holocene. Pollen-based vegetation reconstructions give the best direct view of what the environment of a place looked at a given time and can give us a rough idea of how dominant rainforest was.

The ones below are from the Oak Ridge National Laboratory. They show that for 12,900 and 10,100 years ago, open areas were still widespread in this period, especially at the start²⁷. Rainforest (Rfr) was still somewhat restricted when extinctions began. As a matter of fact, newer climate-based simulations of past vegetation show that for even much of the Holocene, South America had less rainforest area than today⁴⁰.

Moreover, the population crash followed millennia of rising megafaunal density after a low during peak glacial conditions²⁷. This suggests that habitat loss was offset-perhaps considerably-by increased productivity in the remaining grasslands and savannahs (likely due to warming and rising CO₂ levels). In other words, quality was making up for quantity. This does not fit the picture of total megafaunal numbers declining greatly due to an ever-expanding rainforest.

Another aspect to consider in this story involves the dry forests like the Gran Chaco and Caatinga. An intriguing possibility is that South America’s modern distribution of dry forests vs. savannahs may not be entirely natural. Studies indicate that many plants in drier areas exhibit herbivore resistance⁴¹, suggesting they were once heavily consumed by megafauna. Another study finds that South America has far denser tree cover than Africa at comparable moisture levels, potentially because of the absence of large herbivores that would maintain open habitats in the former⁴².

Some dry forests in South America already contain numerous patches of savannah⁴¹. The authors of the second study suggest that if South America’s megafauna still existed, the dry forests could possibly be more similar to savannah broadly, while presently-defined savannahs might be less woody⁴². This would mean a much-less woody continent overall.

There are two key conclusions to be made from this information which both undermine the broken zig-zag hypothesis. First, extinctions hit all types of environments, including closed ones. Second, prime open habitat for megafauna in South America today is likely more widespread than portrayed, and most certainly was when extinctions occurred.

The Big Picture: Extirpation vs. Extinction

Another important thing to keep in mind regarding this topic is the difference between extirpation and extinction. Extirpation refers to regional disappearance of a taxon, whereas extinction proper refers to its complete elimination. The issue when trying to link local faunal shifts to broader patterns is how complex environmental changes can be. A species’ preferred habitat may shrink in one region but remain stable or even expand elsewhere, which can partially or fully offset declines in the former.

While some animals undoubtedly had a hard time during the glacial-interglacial transition as a result of habitat reduction-like the grazers of Beringia-the evidence that this was happening to most species across the board in the Americas is severely lacking. The transition period provided ample habitat for grazers and browsers south of the ice sheets²⁷, although detrimental changes post-extinction of large animals cannot be excluded⁶. Localized environmental changes should not automatically be seen as reflecting broader trends.

Patagonia offers a perfect case study here. A paper postulated that the transition of a section of southern Chile from cold grassland to Nothofagus forest between 13-11 kya was partly responsible for the extinction of grazers there like Mylodon, Lama gracilis, and Hippidion saldiasi ⁴³. However, a larger nearby region in Argentina retained cold steppes through and beyond this period⁴⁴.

And while sea level rise flooded part of eastern Patagonia, it should be noted that megafaunal density was very low in peak glacial times when land extent was greatest³⁹. Density actually rose dramatically from 18 kya until around 13 kya when they crashed in a sudden and unnatural fashion. Thus, losses in land were seemingly being offset by increasing productivity. Ultimately, there seems to be no clear link between extinction and habitat shifts in Patagonia.

All of this demonstrates the give and take nature of habitat shifts in the face of climate change. An informed perspective looking at overarching animal-habitat dynamics rather than localized ones explains why continent-scale correlations between climate and extinction in the Americas are weak or nonexistent²².

Size-Biased Extinctions

It is no secret that the Late Pleistocene extinctions as a whole were heavily size-biased^{18 33 45}. The Americas were no exception in this regard. In fact, there are salient points that drive home exactly how absurdly size-biased the extinctions were in the New World, which raise further doubts about the role of climate as we would expect there to be a somewhat analogous loss of small animals in the event of primarily climate-driven losses like in previous natural extinctions.

A striking fact is that not a single species of megamammal (animal weighing over 1000 kg) survived in the Americas, from Patagonia to the Arctic^{6 33}. American megamammals belonged to diverse groupings, such as proboscideans, giant ground sloths, and glyptodonts. This weight class included species with a wide range of habitats and diets⁶, making it hard to see how they should have been so susceptible to a typical glacial-interglacial transition.

South America, the most biodiverse continent⁴⁶, highlights the size paradox in a surprising but rarely mentioned way. While South American rainforests like the Amazon are renowned for their unparalleled species richness, the tropical/subtropical grassy biomes of South America are also quite biodiverse. Despite losing nearly all of their megafauna, they nearly approach the mammalian diversity of eastern and southern Africa, which retained most of its megafauna^{38 42}. This is because South America, conveniently, managed to preserve its small mammal diversity.

Therefore, climate theorists must address two glaring questions: 1) Why did climate change not spare a single megamammal in the New World and 2) Why did climate change allow South America to retain unequaled small mammal diversity while wiping out nearly all of its large mammals? The size-biased nature of the extinction events remains another problem for environmental theories.

Fecundity

In North America, surviving herbivore species often have shorter gestation periods-which allows for faster reproduction-than their extinct counterparts did. While gestation length generally correlates with size, this pattern holds even when controlling for it. For instance, horses have gestation periods of 11–12 months and camels around 13 months, and this was probably true for their extinct American relatives. Compared to bison, American horses were smaller and Camelops was a similar weight. Yet, bison persisted and the other two did not. Bison, as well as other survivors like elk, moose, caribou, and pronghorn, have gestation periods of under 300 days.

A study speculated that bison survived slightly longer than horses in eastern Beringia due to their “mixed-feeding” habits, but isotopic and dental wear analyses show that both animals had very similar diets^{47 48}. Further, both bison and horse were present on the grasslands of the Great Plains further south but only the former survived, casting doubt on dietary explanations and suggesting a stronger link with reproductive rates.

The survival of species with shorter gestation periods does not align with climatic explanations, as it is hard to see why resource-limited environments would favor more fecund species over slower-reproducing ones.

American Resilience?

With all the talk about environmental change affecting animals in the past, it may be surprising to hear that the Americas were actually blessed in some ways as far as allowing animals to cope with these shifts. But this is exactly what I would argue on the basis of the favorable geographical arrangements on both continents, even in North America in spite of its extreme glacial advances and retreats.

Today, there is a vast expanse of flat grassland in central North America stretching from the Texas Gulf coast all the way to Alberta in Canada-the aforementioned Great Plains. The grassland grades into forest at its eastern boundary, and the forest continues eastwards all the way to the Atlantic. The climate in both the forest and grassland regions of North America ranges from fairly warm in the south to quite cold in the north.

The grassland and forest belts existed during all periods of the Late Pleistocene as well²⁷. Although their exact distribution shifted, the grassland was centrally located and the forest further east. Very importantly, there is no geographic barrier separating the two belts. Animals could move west or east as they needed to to track changes in vegetative openness. Due to the north-south arrangement of these belts, temperate North American animals could track changes in temperature as well.

In South America, the spatial arrangement of biomes is different but there is a similarity in that within the tropical/subtropical zone, the once megafauna-dense savannah, grassland, and scrub are not separated from the major rainforests by geographical barriers. This allows animals to easily move to more suitable areas when the climate changes.

This in stark contrast to Eurasia where the peculiar arrangement of water bodies, mountains, and vegetation zones would create significant obstacles for animals coping with periods of environmental duress. I will write in detail about this topic in a future post about Pleistocene Eurasian extinctions, but my point here is that it should not come as a shock if American megafauna were more resilient than often thought.

There is compelling reason to believe that my hypothesis here holds weight. Gary Haynes has described how severe climatic stress should cause survivors to shrink due to declining food sources¹⁹. Yet, we see that in the Late Pleistocene, the mean mass of animals in both North and South America was similar to that of Africa⁴⁵. This is despite them surviving several previous glacial-interglacial cycles and reinforces the idea that they weathered such changes effectively.

The Case for a Predominantly Human Causation

Let us restate the peculiar features of the extinction event:

• It is the only glacial-interglacial transition to feature such high losses of megafauna.
• Diverse and extremely long-lasting taxa disappeared in a geologic instant.
• The severity of extinctions did not correlate with the magnitude of climatic changes.
• The mechanisms through which climate-driven habitat changes would have led to extinction are either unknown or unconvincing.
• Extinctions were extremely size-biased.
• Survivors tended to have lower gestation periods even controlling for size.

All of these facts are hard to reconcile with a climate-driven extinction but can be explained effortlessly with a human-driven one. This transition was uniquely deadly due to the impact of humans. Extinct species, including generalists and long-lasting taxa, were all highly vulnerable as they faced a novel threat. All regions suffered losses regardless of environmental conditions because they were all settled by people. Size-biased extinctions are expected, as larger animals are more susceptible to human predation^{45 49}. The chance of survival is positively correlated with a shorter gestation period, because these animals offset losses from hunting more easily.

Attempting to explain the extinctions via climate instead of humans invariably results in glaring holes. Dr. Nogues-Bravo and colleagues analyzed extinction patterns across continents and determined that there was a link between climate footprint size and extinction intensity²⁴. The big outlier was South America, which despite having a small climatic footprint, had a high extinction rate (Australia would have been another if it were included). They concluded that climate largely drove extinctions in North America, while “non-climatic factors” were responsible in South America.

This does not make sense. Both continents were settled at about the same time by the same group of people (Paleo-Indians). The animals were equally unfamiliar with humans. Why would climate be the primary cause in one but not the other? A more logical explanation is that humans were the driving force for extinction in both continents, and the greater climate footprint in North America was mostly a coincidence that serves to mask the human role.

For example, while the Younger Dryas cold snap is often blamed for North American extinctions, South America was actually experiencing gradual warming at the time^{19 39}. Yet extinctions still occurred there near-simultaneously. Therefore, the coincidence of North American extinctions with the Younger Dryas should not automatically be taken as proof that it, or any climate event, was the responsible force.

Non-climate factors can even explain South America’s greater extinction rate. South American megafauna were larger on average than North American ones, and we know the extinctions were size-biased. Additionally, native (pre-Great American Biotic Interchange) South American animals evolved in a milieu with far less dangerous predators compared to their North American counterparts⁵⁰, potentially making them more defenseless against the human super-predator. The fact that almost all surviving mammalian megafauna in South America-deer, tapirs, big cats, llama relatives-are North American migrants from the GABI³³ would further support this point.

A False Middle Ground?

Throughout this post, I have referenced the common view that both climate and humans played substantial roles in American megafauna extinctions^{3 4 33}. By avoiding single-cause explanations, these perspectives appear nuanced and intuitive, and often come in the form of describing these factors as “synergistic” rather than additive³³. Even many overkill proponents posit a climatic influence⁵¹.

Although I admire and cite many experts who hold this view, I take issue with this framing. First, Australia demonstrates that a major input from climate change is not required for continental extinctions. Second, we must clarify what it means for a factor to be “necessary” or to have “contributed.” If it simply means climate and humans influenced the timing and specifics of extinctions, that is understandable. But if it implies that most megafauna could have survived into the modern era if dealing with only one factor rather than both, it is questionable.

If climate had a large but not exclusive input in driving extinction(say 30–50%), we should still see a noteworthy correlation between climate change intensity and extinction severity, or between species specialization and vulnerability. Yet, such patterns are almost entirely absent. While some animals may have been highly sensitive to climate shifts, their dynamics are certainly not representative of all species in the Americas.

The overall evidence suggests that human-related factors (which I will expand on in the next post) sufficiently explain broad extinction patterns. At present, I would argue climate change’s overall impact was likely minimal.

Multifactor hypotheses remain popular, partly because they are harder to refute than climate-centric models which have become increasingly untenable. Regardless of whether one favors a major or minor role for climate, an objective assessment would recognize that human actions doomed at least a large portion of the New World megafauna independent of environmental conditions.

Megamammals are good candidates for inevitable extinction. Despite their diverse ecologies, all of them perished⁶. In that context, does it make sense to debate whether hypothetical habitat reductions, such as for mastodons in the southwestern U.S., “contributed” to their demise? Given the total extinction of this weight class, it is reasonable to believe humans would have wiped them all out even under ideal conditions.

This extends beyond the largest species. Cione et al. (2009) note that South America’s surviving megafauna mostly inhabit inaccessible areas like mountains, dense forests, and wetlands³³ and are overwhelmingly Holarctic migrants. While the authors argue that rainforest expansion contributed to extinctions, such shocking facts speak for themselves. In a scenario where the environment remained unchanged from 15 kya onwards, would plains-dwelling megafauna have fared much better against growing human populations armed with increasingly lethal hunting tools¹⁸? The answer seems evident.

Conclusion and Sequel

In this post, we have established the weakness of climate change in comparison to humans in explaining the Late Pleistocene extinction mystery in the Americas. Despite the indisputable presence of major climate shifts during the extinction window, the evidence overwhelmingly rules out climate as the dominant factor in megafaunal loss. Multifactor theories wherein climate was a necessary component alongside humans are popular but ultimately suffer from many of the same issues.

Big-picture thinking is key to solving the debate. As I have shown here, continent-wide analysis is necessary, and appropriate comparisons between continents can be valuable-as with North and South America. North America’s losses cannot be analyzed without also considering South America’s extinction patterns, which throw a wrench into climate narratives.

However, there is still much more to explore on this topic. The evidence for human predation on megafauna, the intricate relationship between human settlement and megafaunal decline, and the specific mechanisms driving these extinctions all warrant further discussion. These aspects will be the focus of the next installment in this series.