Mysterious disappearance of megafauna: why humans may share the blame

• There have been six megafaunal extinctions since the Late Pleistocene.
• The most recent of these fell between 18,000–11,000 years ago in South America, 30,000–14,000 in North America, and 50,000–32,000 years ago in Australia. 
• Coincidentally, or perhaps not, these also happened at the same time as early humans settled those areas, but was that the cause?

The Pleistocene Epoch, often referred to as the "Great Ice Age," was when the Earth's climate changed significantly, and large, amazing animals called megafauna appeared.

These massive creatures roamed the Earth for more than two million years before disappearing around 10,000 years ago.

But why did they disappear? Was it from natural causes, or perhaps, was our species to blame?

Come with us on a journey to discover the incredible megafauna of the Pleistocene Epoch and discover some of the most plausible theories and explanations.

What was the megafauna?

More accurately called the Pleistocene megafauna, they were a group of enormous animals that inhabited Earth throughout the Pleistocene period (roughly between 2.5 million and 11,700 years ago).

The latter date, 11,700, corresponds with an event known as the Younger Dryas, which we'll discuss in more detail later.

During the Quaternary extinction event, many Pleistocene megafaunas became extinct, drastically altering ecosystems worldwide. The cause for this is very much a matter of heated scientific debate, but theories range from humans or climate change being the leading causes.

The classification of a member of the megafauna typically includes animals (usually mammals) whose size is more than 99 pounds (45 kilograms).

The types of creatures included in this classification vary from continent to continent.

For instance, the Australian Pleistocene megafauna includes the enormous Diprotodon, which resembled a giant wombat, and the enormous Megalania goanna.

Some of the most notable examples that lived in Europe include mammoths, cave lions, cave bears, straight-tusked elephants, interglacial rhinoceros (Stephanorhinus), heavy-bodied Asian antelope (Spirocerus), Eurasian hippopotamuses, woolly rhinoceros, gigantic deer, saber-toothed cat (Homotherium), and the leopard.

Of all megafauna that ever existed, most of the remaining species can be found in Africa. But what happened to the rest?

Let's take a look at the most prevalent theories.

What wiped out the megafauna?

We are not entirely sure, but megafauna worldwide likely became extinct due to ecological and environmental reasons. Whatever the cause, we do have a good idea of the timing.

Fossil evidence from numerous continents indicates that megafauna animals went extinct at or close to the end of the last glacial period. Various megafauna appears to have gone extinct at different times.

Still, the overall trend over a few hundred thousand years points to the large-scale wiping out of most of the larger animals of the day.

For example, the straight-tusked elephant went extinct in Eurasia between 100,000 and 50,000 years ago. Between 50,000 and 16,000 years ago, the Eurasian hippopotamuses, interglacial rhinoceros, heavy-bodied Asian antelope, and cave bears (Ursus spelaeus) also vanished.

The saber-toothed cat (Homotherium), the cave lion, and the leopard disappeared from Europe 28,000, 11,900, and 27,000 years ago. Between 16,000 and 11,500 years ago, the woolly rhinoceros and the last mammoths died too.

After 11,500 years ago, the big deer vanished, with the last pocket remaining in western Siberia until about 7,700 years ago. 

However, the extinction event was not total. A small population of mammoths was still present on Wrangel Island 4,500 years ago.

So, what happened to them?

As we've previously mentioned, the currently most supported theories include pressure from climate change and the possible impact of human hunting.

As for the former, scientists have managed to reconstruct how the climate changed throughout this period. A series of severe and quick climate changes, with regional temperature swings of up to 16 °C, characterized the Late Pleistocene and have been linked to the extinction of large mammals.

However, megafaunal extinctions during the height of the last glacial maximum (LGM) do not appear to have occurred, indicating that growing seasonality and the subsequent changes in available plants were not the sole cause.

While climate change appears to have been bad for large mammals, the climate changes of the time might have benefited our early ancestors.

Roughly 195,000 years ago, the ancestors of modern humans first appeared in East Africa. Some left Africa roughly 60,000 to 90,000 years ago, with one group eventually making it to Central Asia roughly 50,000 to 40,000 years ago.

From there, people traveled to Europe. Human remains dating to 43,000–45,000 years ago have been found in Italy, Britain, and the European Russian Arctic.

Around 27,000 years ago, another group left Central Asia and made it to the lower Yana River in Siberia, which is well above the Arctic Circle. In the central Siberian Arctic, at Yenisei Bay, mammoth remains that humans hunted 45,000 years ago have been discovered.

Between 20,000 and 11,000 years ago, when the Wisconsin glacier had retreated, but before rising sea levels submerged the Bering land bridge, modern humans made their way across the Bering land bridge and into North America.

However, there is still disagreement among academics over the timing of human migration to the Americas. 

The first agricultural practices appeared in the Fertile Crescent 11,500 years ago.

Megafaunas are thought by some to have evolved initially in response to glacial circumstances and to have gone extinct with the arrival of warmer temperatures and the changes to vegetation this brought.

Megafauna extinction in temperate Eurasia and North America ended simultaneously as a sizable expanse of forest replaced the huge periglacial tundra in both regions. Elk, deer, and pigs, better suited to forests, supplanted glacial species like mammoths and woolly rhinoceros.

Horses moved south to the steppes of central Asia while reindeer (caribou) moved north. Even though humans just began to colonize non-tropical Eurasia and non-tropical North America less than 15,000 years ago and 10,000 years ago, respectively,

Areas that are tropical or subtropical have seen less drastic climatic change. The most notable of these changes was converting a sizable portion of north Africa into the greatest desert on the planet. Africa and tropical and subtropical Asia both avoided catastrophic faunal extinction, which allowed some of the continent's megafauna to survive to the modern day.

Asian elephants continue to exist today, along with Asian rhinoceroses, even on the comparatively small Indonesian island of Java.

Australia's climate transitioned from cold-dry to warm-dry after the last ice age. Surface water became scarce as a result. Most interior lakes dried up entirely or partially during the warmer months. In eastern Australia, where there was permanent water, and greater vegetation, most large, primarily browsing animals lost their environment and relocated there.

So, much like the dinosaurs before the Chixculub impact, megafauna appears to have been on the out. But, around 11,700 years ago, something dramatic ended almost all of the rest.

But what could this have been? Let us introduce you to something called the Younger Dryas.

What was the Younger Dryas?

The gradual climatic warming after the Last Glacial Maximum (LGM — between 27,000 to 20,000 years ago) was momentarily reversed during the Younger Dryas (roughly 12,900 to 11,700 years ago), which saw a return to glacial temperatures.

The Younger Dryas was the final stage of the Pleistocene epoch (about 2,580,000 to 11,700 years ago), before the start of the present, warmer Holocene epoch. It was preceded by the Late Glacial Interstadial, the worst and longest of several breaks in warming the Earth's climate (between about 14,670 to 12,900 ago).

This was a relatively abrupt transition, which occurred over decades, leading to a 13.7 °C (7.218 °F) decrease in Greenland's temperature and the advancement of glaciers and drier conditions across a large portion of the temperate Northern Hemisphere. At the same time, a slight warming occurred in the Southern Hemisphere and several regions of the Northern Hemisphere, including southeastern North America. 

This would have been a very tough event to live through, and many animals and plants, as well as our ancestors, would have been stretched to their limits. Despite our incredible adaptive capacity, some research indicates that our species suffered a massive decline in population during this period.

The collapse in the human population appears to have been quite severe. In fact, evidence for this collapse can be seen in our DNA as a "bottleneck" event.

What's more, and very controversially, it has been argued by a few that this event may have also destroyed some ancient "advanced" civilizations. However, while this theory is attractive, it is not widely supported by archaeologists.

But how could this have happened?

The most widely accepted theory among scientists regarding the cause is that an influx of fresh, cold water from North America into the Atlantic disrupted the Atlantic meridional, overturning circulation which moves warm water from the Equator towards the North Pole. 

This was most likely caused by a significant influx of fresh water from glacial melt lakes that flowed into the oceans.

Why this happened is very much up for debate, but either there was a sudden failure of natural levees or dams that held back the water, or some other violent event caused the mass melting of ice in a short period.

There is also growing evidence that the Younger Dryas might have been caused by something literally out of this world - a comet or asteroid impact.

Called The Younger Dryas impact Hypothesis (YDIH), also known as the Clovis comet hypothesis, this theory is proposed as an alternative to the more general idea that the Younger Dryas was the result of a significant reduction or shutdown of the North Atlantic "Conveyor" in response to a sudden influx of freshwater from Lake Agassiz and deglaciation in North America.

According to the YDIH theory, a massive (more than 2.48 miles/4 kilometers in diameter), evaporating asteroid or comet fragment struck Europe, western Asia, North America, and South America 12,850 years ago, coincided with the start of the Younger Dryas cooling episode.

The Younger Dryas boundary layer (YDB), created by numerous meteor air bursts and impacts, is thought to have deposited peak concentrations of platinum, high-temperature spherules, melt glass, and nanodiamonds at more than 50 sites across about 19.3 million square miles (50 million km2) of the Earth's surface, creating an isochronous datum.

According to some experts, this event caused significant biomass burning, the Younger Dryas' abrupt climatic shift, a short impact winter, the extinction of late Pleistocene megafauna, and the end of the Clovis culture in North America.

This theory is very appealing and would undoubtedly explain something like the Younger Dryas, but it must be acknowledged that the scientific community does not widely accept it. However, it does have some interesting evidence to back it up.

For example. the existence of microstructures (spherules) and "black mats" of sediment, which the theory's proponents claim are proof of widespread fires. Proponents also point to suggested dates for the Hiawatha crater in Greenland, in the range of 12,800 years ago (though later dating has indicated it came from an event from 55 million years ago), and the synchronous extinction of megafauna and related effects on prehistoric human societies have all been offered as evidence for the impact event.

According to the concept's proponents, these data are insufficiently explained by volcanic, anthropogenic, or other natural processes. They contend that the Younger Dryas boundary layer should be employed as a regional, global, or stratigraphic marker.

The existence of a layer of nanodiamonds, metallic microspherules, carbon spherules, magnetic spherules, platinum, platinum/palladium ratios, charcoal, soot, and fullerenes enhanced with helium-3 are among the substances that proponents—the majority of whom are scientists—have reported as supporting evidence for an impact event that initiated the Younger Dryas.

But, if there was a bolide impact, where is the crater?

If the impactor (comet or asteroid) hit the extensive ice sheets of the planet at the time, it could be the case that we'll never find a crater. Much like murder with a weapon made of ice, the "crater" would now be long since melted away.

However, there are some potential candidates. A 2018 research offered evidence for a potential impact crater under the Hiawatha Glacier in Greenland, which was assumed to have formed sometime during the Pleistocene.

Kurt Kjaer, lead author on a paper discussing this crater, said that the team was confident of the link between the Hiawatha and the Younger Dryas.

However, since it would have left behind evidence like a young ejecta blanket, skeptics disregarded this connection because it would have required an unusually recent impact, evidence for which would be easier to find.

So, this means humans are off the hook, right? Probably not.

Were humans the cause of the megafauna extinction?

In short, it isn't an easy question to answer. For some megafauna species, probably, but for most others, probably not. The climate was far from stable during this time, and humans were not just predators during the Pleistocene; we were also prey, hunted by larger predatory mammals too.

But, before we get into the weeds, it is essential to understand the scale of the loss of life during this period. Although, it is difficult to give an exact percentage of megafauna that died during the Pleistocene, as it varied widely among different regions and species.

It is estimated that a significant number of megafauna species went extinct during the Pleistocene, particularly during the Late Pleistocene (around 126,000-11,700 years ago). Some estimates suggest that up to 50 percent of megafauna species may have gone extinct during this period. In North America, estimates have been quoted as high as 70 percent of the region's megafauna species.

The extinction of megafauna around the world at the end of the Pleistocene period, around 11,000 years ago, is a complex and controversial topic in paleontology and anthropology. The question of whether human activity was the cause of this extinction is still debated among scientists.

This is especially the case as human populations would have been relatively low at the time, with estimates of around 1,000,000 worldwide. To put that into perspective, there are about 1 billion sharks alive today, and human population levels at the time are about the same as the number of bears alive today.

Evidence supports both human and non-human causes for the extinction, and a combination of factors likely led to the loss of these animals.

One theory is that human hunting and overhunting was the leading cause of the megafauna extinction. According to this theory, human populations expanded rapidly after the last ice age and began to hunt these animals for food, resulting in their overhunting and eventual extinction.

This theory is supported by the fact that many of the animals that went extinct, such as mammoths, mastodons, and giant ground sloths, were large, slow-moving creatures that would have been relatively easy to hunt.

Furthermore, many of these animals were known to be hunted by early human populations. There is evidence of human hunting of these animals in the form of artifacts such as spear points and butchering tools found in association with the animals' remains.

Another theory is that natural climate change, rather than change from a meteor impact, was the leading cause of the megafauna extinction. According to this theory, the rapid warming that occurred at the end of the last ice age led to changes in vegetation patterns and animal migrations, leading to many large mammals' extinction.

This theory is supported by the fact that many of the animals that went extinct were adapted to cold Arctic environments and would have been unable to survive in the warmer climates that developed after the last ice age.

Furthermore, there is evidence that many of these animals were dependent on specific types of vegetation, such as mosses and lichens, which would have been adversely affected by the warming climate.

A third theory is that a combination of human activity and natural causes led to the extinction of the megafauna. According to this theory, human hunting and climate change likely both contributed to the decline of these animals.

Still, a more proximate cause could also have contributed to their extinction, in the form of a catastrophic event such as a comet impact, volcanic eruption, or epidemic disease outbreak.

This theory is supported by the fact that many megafauna extinctions occurred relatively rapidly, in a time frame consistent with a catastrophic event.

In summary, the megafauna extinction that occurred around the end of the Pleistocene period is a complex and multifaceted event that is likely the result of a combination of factors.

Human hunting and overhunting, human-induced climate change, and possibly a catastrophic event such as a comet impact, volcanic eruption, or epidemic disease outbreak are all likely to have played a role in the extinction of these animals.

Currently, no single theory thoroughly explains the extinction event. More research is needed to understand the complex interactions of the different factors that contributed to the loss of these animals.

What, if any, megafauna still exists?

Well, you, for one.

Adult humans tend to average around 147 pounds (67 kg) in weight, so we meet the term's criteria. But that's not really what people mean when they ask questions like this.

Other than us, there are plenty of animals worldwide that are, technically speaking, megafauna. Most of the large mammals in Africa being the prime examples: elephants, lions, other big cats, giraffes, and rhinoceros, to name a few.

Further afield, other large mammals, like tigers, panthers, moose, elk, and marine mammals, also fit the bill. Most of these evolved during the Pleistocene and have survived to the modern day.

What are the most exciting megafauna animals that were lost during the Pleistocene?

All very interesting, but what creatures were lost during the period of great change for the planet? Let's take a look at some of the most notable examples.

The following are from the late Pleistocene and are primarily those lost during the Quaternary mass extinction event.

1. Glyptodon is one of the strangest animals you've ever seen

Large armored mammals called glyptodons went extinct about 10,000 years ago. The glyptodon, around the size of a Volkswagen Beetle, was well-protected from predator attacks.

They were related to modern-day armadillos and could not withdraw their heads into their shells like turtles. Thus, they had to rely on their sharp spikes and heavy skull armor to protect them. Their thick tail had a bony bump at the end and could be wielded as a club, much like the dinosaur ankylosaurus.

Scientists believe they ate almost anything, including plants, insects, and carrion.

2. Megalania must have been a scary creature to meet

An extinct species of giant monitor lizard called Megalania (Varanus priscus) lived in Australia during the Pleistocene and was a member of the megafaunal assemblage. With an estimated length of 11.5 - 23 feet (3.5 to 7 meters) and a weight of between 214 and 4,277 pounds (97 and 1,940 kilograms), it is the giant terrestrial lizard known to have existed.

However, estimates of its size are highly speculative due to the fragmentary nature of the known remains.

Megalania's ecology is believed to be similar to that of the Komodo dragon today (Varanus komodoensis). The earliest fossil evidence of enormous monitor lizards in Australia dates from 50,000 years ago. Megalania may have been encountered by the first native Australian settlers, who may also have contributed to its extinction.

Australian Aboriginal people and megalania may have had conflicts, which may be what gave rise to legends of terrifying monsters like the "whowie."

Due to its striking resemblance to other Australian monitor lizards, megalania is now considered a member of Varanus rather than the original genus of which it was the sole member.

3. Megalonyx was a gigantic ground-dwelling sloth

Megalonyx, which means "big claw" in Greek, was a genus of extinct ground sloths that lived in North America throughout the Pliocene and Pleistocene eras. It lived from around 5 million to 11,000 years ago and went extinct during the Quaternary extinction event at the end of the Rancholabrean period of the Pleistocene.

This species, M. jeffersonii, was up to 2,200 lb (1,000 kilograms) in weight and roughly 9.8 feet (3 meters) long (2,200 lb). Megalonyx is a descendant of Pliometanastes, a genus of ground sloth that arrived in North America before the Great American Biotic Interchange during the Late Miocene.

Megalonyx was the most widespread ground sloth in North America. Its range included most of the country's contiguous states and occasionally reached as far north as Alaska.

4. There was once a tiny pygmy mammoth

The extinct pygmy mammoth, also known as the Channel Islands mammoth (Mammuthus exilis), was a tiny relative of the Columbian mammoth of mainland North America (M. columbi).

This species went extinct during the Quaternary extinction event, which also saw the demise of numerous megafauna species due to environmental changes to which the species was unable to adapt.

M. exilis, is believed to have had an average height of just 5.6 ft (1.72 m) tall at the shoulders and (1,680 lb (760 kg) in weight. This is a marked contrast to its much taller and heavier ancestor.

The cause of the extinction of the pygmy mammoth is unknown, but it could have been caused by overhunting by humans, wildfires, climate change, or some combination thereof.

5. The mammoth is probably the most iconic megafauna

Following in nicely from the pygmy mammoth, its full-scale mammoth ancestor is probably the most iconic of all lost megafauna.

Mammoths (originally from the Russian ма́монт" (mámont), meaning 'Earth Horn') are one of the numerous genera that make up the class of trunked mammals known as proboscideans. The several mammoth species were all typically armed with long, curved tusks and, in northern species, a coat of long hair.

They existed in Africa, Europe, Asia, and North America and lived from the Pliocene epoch (about 5 million years ago) into the Holocene, until roughly 4,000 years ago.

The species belonged to the same family as current elephants and their forebears, including the two genera of extant Elephantidae - African and Asian elephants. African elephants are more distantly related to mammoths than Asian elephants are.

The South African mammoth (M. subplanifrons), the first known member of the Mammuthus genus, first arrived in what is now southern and eastern Africa about 5 million years ago during the early Pliocene.

The Columbian mammoth's ancestors were a descendant species of these mammoths that went north and continued to breed, eventually populating most of Eurasia before migrating to North America 1.5–1.3 million years ago (M. columbi).

The woolly mammoth (M. primigenius), the last species to appear, appeared in East Asia about 400,000 years ago. Some of these animals continued to exist as recently as around 4,000 years ago when the Great Pyramid of ancient Egypt was being built.

These last survivors lived on Russia's Wrangel Island in the Arctic Ocean and possibly on the Taymyr Peninsula in mainland Siberia.

6. Smilodon probably hunted our ancestors

Smilodon is the most well-known saber-toothed cat and one of the most well-known prehistoric mammals. Despite being commonly known as the saber-toothed tiger, it was not closely related to the tiger or other modern cats.

Smilodon lived between 2.5 million and 10,000 years ago) on the American continents. Based on fossils found in Brazil, the genus was given its name in 1842, with its name translating to "scalpel" or "two-edged knife" plus "tooth."

S. gracilis, S. fatalis, and S. populator are considered three distinct species of Smilodon. The largest collection of Smilodon fossils comes from the La Brea Tar Pits in Los Angeles, where hundreds exist.

Smilodon had a more muscular build than any cat alive today, with exceptionally well-developed forelimbs and unusually long upper canine teeth. Its top canines were slender and delicate because they were designed for precision killing, and its jaw gaped more than that of modern cats.

Smilodon was effective even when it encountered new prey species in South America while hunting giant herbivores like bison and camels in North America. Although it is unknown how the bite was administered, it is believed that Smilodon killed its prey by holding it immobile with its forelimbs and then biting it.

It most likely also preyed on our ancestors.

Scientists disagree on whether Smilodon lived in a gregarious or solitary environment; nevertheless, both views may be supported by examining contemporary predator behavior and the fossil evidence for Smilodon.

Smilodon most likely resided in closed environments like woodlands and bushes, which would have offered shelter for prey ambushes.

This terrifying large cat perished around 10,000 years ago, around the same time as most of North and South America's megafauna. Along with climate change and competition with other species, its dependency on large animals has been suggested as the reason for its extinction.

However, the precise cause is uncertain.

And that is your lot for today.

The Pleistocene was a period of rapid and dramatic climate change for the planet. This partly contributed to the downfall of many large mammals of the day but appears to have played well into our early ancestors' hands.

Forced to adapt or die, our early ancestors spread out of Africa and quickly colonized many parts of the world. While undoubtedly, humans would have hunted for food, it seems very unlikely that that was the sole cause of the series of mass extinction seen throughout the period.

But, much like the dinosaurs that preceded them, their fate appears to be the classic triumvirate of changing climate, competition, and, perhaps, an extraterrestrial coup de grâce.