What Killed the Megafauna?
A Land of Monsters
We live in a biologically impoverished world, a world where all of the hugest, fiercest and strangest creatures have disappeared. To get an idea of just how impoverished most of the world is today; imagine taking a trip to a place billed as one of the last great wildernesses, the northern Canadian pine forests. Nature documentaries often give the impression that moose and bears lurk behind every tree, but sadly it seems that this is not the case. I’ve watched documentaries where people have trekked through these very same forests of which I speak for days and weeks and found nothing except maybe some moose tracks and the odd black or brown bear at a distance. Yet, whenever I watch footage of the African Serengeti, I am constantly blown away by the sheer abundance and diversity of megafauna on show. In fact, I remember watching a documentary featuring survival expert Ray Mears, and he told of a funny story he’d heard from a safari lodge manager about how a tourist had decided to go for a jog during the early hours of dawn. Luckily this manager was already up and about patrolling the area, he spotted the naïve tourist and quickly bundled him into the jeep and said: ‘What do you think you’re doing? Going to feed the lions?’ This is a funny, yet sobering reminder that most of us have no idea what it’s like to live alongside dangerous large animals.
Of all the places in the world, Africa is the place that we associate with wildlife, because it still has its marvellous monsters. In the recent past, the rest of the world was not so different and the evidence for that lies right beneath our feet. Buried deep in the ground are the remains of some of the most bizarre and spectacular animals that ever walked the Earth. They thrived for millions of years, evolving and adapting to whatever environmental challenges they encountered. But during the latter stages of the Pleistocene epoch (1.8 million years ago-10,000 years ago) they suddenly and mysteriously disappeared. The scale of this vanishing is alarming: South America for example lost 80 per cent of its large animals, its northern neighbour lost 73 per cent, Eurasia 30 per cent, Australia 86 per cent and the oceanic islands which took the biggest hit of all lost a staggering 95 per cent. So what on earth happened to them?
Of course, extinction is a natural process, and all species disappear eventually, someday the same fate will befall us. Over millions of years, new species evolve, while old ones fade away, but there are times when the extinction process is accelerated dramatically; it’s an event where a large number of animals disappear en masse in a relatively short period of time. Whenever this happens, scientists call them mass extinctions. In Earth’s history, there have been five such mass extinctions, the last of which occurred 65 million years ago when the dinosaurs and other large reptiles disappeared. Mass extinctions are normally identified by their impact on small marine creatures, whose shells usually fossilise well, but the Pleistocene extinction was different, it failed to kill off enough species to truly qualify a true mass extinction. However, it remains the most devastating loss of large animals since the extinction of the dinosaurs.
Discovering the cause is very important, as the very same forces that wiped out the megafauna could perhaps one day overwhelm us. Many different hypotheses have been proposed to explain this phenomenon, but there are three particular hypotheses that tend to be favoured by experts. These are disease, climate change and human overkill - which one is correct?
We’ll start with a fairly obscure, but still credible theory that a highly infectious disease perhaps transmitted by humans or domestic dogs was responsible. The two main proponents of the theory are Ross MacPhee of the American Museum of Natural History and Preston Marx of Tulane University in Louisiana. They point out that long established diseases tend to evolve a benign relationship with their host, because destroying the host completely would prevent any future chance of transmission. In contrast, newly emerged diseases, which can form when viruses or bacteria jump the species barrier, tend to be lethal. A good example of this is the AIDS virus in humans, which emerged in the 1950s after the virus jumped from African monkeys to us through increased contact. Emerging diseases may be harmless to their ancient hosts but deadly to any new ones, and they are more likely to appear when two previously isolated species all of a sudden come into close contact. Is it possible that increased contact between man and megafauna triggered a lethal epidemic sufficient enough to wipe out all of the hugest, fiercest and strangest animals across the globe?
The main problem with this theory though is that the extinct megafauna not only included mammals, but also birds and reptiles. It’s unlikely that such a diverse range of animals would be all susceptible to the same microbe. Even so, scepticism from the wider scientific community hasn’t deterred MacPhee and Marx; they’ve already begun searching the tissue of frozen mammoths for bugs that could have caused a global Pleistocene epidemic, but thus far their hard work has met with little success, they still lack the concrete evidence that would validate their theory, so for now it remains conjecture.
Did a Virus Wipe out the Megafauna?
An In-Depth Look at the Pleistocene Megafauna Extinction
- Quaternary extinction event - Wikipedia, the free encyclopedia
This link includes an extensive analysis of the climate change hypothesis as well as looking at all the other proposal so far submitted.
Climate change certainly looks strong on paper, as there is plenty of evidence that it can exterminate animals. In fact, each of the previous big five mass extinctions is associated with drastic global climate change. But what exactly caused these wild temperature swings, and were these same forces responsible for ending the Pleistocene megafauna?
For most of the previous century, scientists argued over why the dinosaurs died out; while they all agreed that climate change was responsible, they quarrelled over exactly what had caused that changes. All of sorts of different factors were proposed including sunspot activity, changes in Earth’s orbit, continental drift, volcanoes and an asteroid impact. The debate rolled on for decades until a giant impact crater was found in Mexico, the size and timing of which corresponded with a global layer of ash and iridium (an element that’s rare on Earth but common in meteorites) in ancient rock strata. It’s unlikely that the megafauna suffered the same fate as the dinosaurs, because as of yet no big craters or iridium layers dating from the late Pleistocene have been found.
What about other climatic factors? Continental drift can be ruled out because there simply hasn’t been enough time for the continents to move substantially. Also, there is no evidence of any massive volcanism or lethal charges in solar radiation.
In North America, there have been at least six mini extinctions over the last 10 million years, with the end-Pleistocene disaster ranking only second in terms of the overall number of victims, but first by a large margin in terms of the number of large animals going into the dark. The earlier extinctions all coincided with a warming period at the end of previous ice ages, long before the arrival of humans. Some scientists have speculated whether it was changes in the distribution and availability of vegetation that ended the megafauna. This of course would have required drastic swings in temperature to occur. Or perhaps it was some sort of ecological ripple effect; maybe, as key species vanished ecosystems became disrupted forever, thus hastening the extinction. In modern times, we can still see iconic megafauna such as elephants influencing their landscapes. Just through their normal daily activities, they can turn forests into grasslands, and thus alter the fortunes of other species. These hypotheses attempt to distance themselves from climate change, citing habitat change as the biggest factor, but really any hypothesis that highlights habitat change is really a climate change hypothesis in disguise as climate is the biggest factor in governing a habitat.
While climate change can certainly exterminate life, attempting to apply it to the extinction of the Pleistocene megafauna exposes a number of flaws, which I will outline below. For me at least, the finger of blame points squarely in a very different direction.
An Excellent Link
- Megafauna - "First Victims of the Human-Caused Extinction" - book by Baz Edmeades
How our species exterminated most of the planet's big, land-dwelling animals before the advent of written history. A pro-overkill e-book written by Baz Edmeades.
When the first Ice age animals were discovered and described in the nineteenth century, some palaeontologists proposed that hunting by humans was responsible for their disappearance. The most famous modern champion of this hypothesis, known as ‘overkill’ was the late Paul Martin of the University of Arizona. Paul spent his career arguing that human hunters inadvertently exterminated the megafauna as they spread across previously uninhabited lands. Below I shall highlight certain facts that about the Pleistocene extinctions that cannot be explained by any form of climate change.
- The spread of the extinction dates: If global climate change did indeed kill off the megafauna then all of the extinctions should have taken place simultaneously. But an examination of the dates for each continent reveals something significant. North America, for example lost its megafauna around 12,000 years ago, while Australia lost theirs over a broader period, but mostly around the 40,000 years ago mark, and finally the islands did not experience any extinctions until around 4000 years ago. These dates are rather erratic in terms of attempting to apply a climate change theory, but they do show a suspicious correspondence with the arrival of humans.
- Size and lifestyle: Climate and disease theories struggle to explain why large animals and flightless birds were more likely victims. This rather odd pattern is absent from all other mass extinctions. In many areas of the world, the survivors tended to be small, fast poisonous, tree dwelling or nocturnal, while the victims were rather slow, terrestrial and diurnal. Climate change does not discriminate in this way, but hunters do.
- Naïve animals: Many of the New World victims were native species, without any experience of modern humans whatsoever. In contrast, when you take a look at the surviving American megafauna (moose, elk, bison, caribou and musk-ox) they are all in fact recent Eurasian colonists just like humans. The truly native animals had little instinctive fear of humans and thus would have been easy targets for hunters. Climate change cannot explain why the African and Eurasian megafauna fared so much better than their American and Australasian brethren; but overkill can because the animals that were accustomed to us had evolved ways of defending themselves.
- Delayed extinction on islands: Long after the megafauna disappeared from the continents, some did survive on islands for up to several thousand years longer. For example, Woolly mammoths survived on Wrangel Island in the Arctic until 4000 years ago, but disappeared from both North America and Eurasia more than 10,000 years ago. Ground sloths survived in Cuba more than 4000 years longer than in North America. The climate of these islands was virtually identical to that of associated mainlands.
- Reintroduced megafauna thrive: If climate induced habitat change destroyed the megafauna, then reintroduced relatives should have difficulty surviving in the new habitat. Yet, horses reintroduced to the New World by the Spanish have spread right across the American West so successfully that they are now a pest. Similarly, European wild boar, llamas and capybara also thrive in modern America; they are all related to extinct Pleistocene fauna. Another example is the musk-ox which has been successfully reintroduced to their former ranges in Siberia, Scandinavia and Alaska.
Connie Barlow Talks About the Megafauna Extinction
A Megafaunal Graveyard
Where's the Evidence?
A criticism of the overkill theory that surfaces every so often is the fact there is little archaeological evidence to prove humans hunted the megafauna to extinction. But evidence does exist. In New Zealand for example, vast piles of moa bones fill ancient Maori refuse dumps, while kitchen middens throughout Pacific islands contain the remains of numerous extinct species. In the Americas, mammoth bones bear telltale marks of human butchery and weapon damage. Also, the blood of an extinct horses has been identified on the end of Clovis spear-points. In Eurasia, evidence exists that shows that our ancestors did hunt aurochs and woolly mammoths regularly.
Of all the continents, Australia seems to be the one lacking evidence, with the exception of the Cuddie Springs site which has yielded evidence of human butchery marks on megafauna bones. It does seem rather puzzling that evidence for human hunting in Australia is scarce at best; did humans and the megafauna actually co-exist over a long period of time? Is Australia the anomaly? Did climate play a bigger role here than elsewhere? Peter Murray of the Central Australian Museum thinks not. He suspects that another form of human interference played a much bigger role than hunting- burning. There is mounting evidence that the ancient settlers of both Australia and Madagascar used fire to change the landscape. Though Australia experiences frequent wildfires in the dry season, humans altered the natural cycle by setting fire to the landscape at other times of the year. Such a change would have had a profound impact on plant life, which of course would have had severe consequences for animals.
Scientists often attempt to try to make peace among the warring academic camps by arguing that the megafauna succumbed to a combination of factors, often suggesting that climate change and human hunting combined to push them over the edge. But while scientists struggle to unravel the full story, the evidence so far points to one culprit- Homo sapiens. As we spread throughout the world, armed with fire, weapons and intelligence we met monsters, creatures scarcely within the realms of human imagination and yet, in our wake we left a trail of death. Where once huge, fierce and strange monsters roamed, now stands vast swaths of silent forests and empty grasslands. Ours is a world of boring uniformity, its megafauna annihilated. Are we instead the real monsters?