Did humans wipe out the megafauna?

The wonderful thing about writing for Twilight Beasts is the chance to bring back some truly incredible creatures. Here we are allowed to be taken back to a time when the largest land lizard ever walked the Earth: Megalania. We can feel the heat of the Australian sun, as we watch this oversized komodo dragon stalk a marsupial the size of a VW Beetle, the wonderful Diprotodon. Or perhaps we enjoy imagining we are sitting on the edge of a rich lagoon, with enormous tank-like Glyptodon taking a drink, unaware of a pride of Smilodon in the bushes. Or for those who like a more chilly time, step back onto the cold Steppes of Eurasia to see herds of Mammoths lolloping across the grassy plains, as a lone woolly rhinoceros munches quietly on the low shrubs.

A quick hop across the globe just a few tens of thousands of years ago, and there would have been some incredible animals to see. The world as we know it would be completely different. Strange, but so beautiful. Los Angeles would have been an open landscape with Mastodons and dire wolves. The swampy marsh lands of Florida home to many giants, like Glyptodonts and giant sloths. Musk ox and Bison would have shuffled slowly through icy winds in Britain.

And then something happened. These beasts vanished.

A typical scene in Late Pleistocene Europe around 30,000 years ago. (Image by Mauricio Antón. Public Domain)

Giants across the globe disappeared forever. These wonderful creatures were just a whisker away from the present day. This was the great Pleistocene megafaunal extinction, which some scientists are beginning to call the 6^th mass extinction. (Megafauna are animals weighing over 44kg, so something the size of a big Alsatian is classed as megafauna.) Extinctions have happened many times in the 4 billion years of life on Earth. Species come and go. Even mass extinctions happen. These are bigger, and more deadly than your average extinction.

A mass extinction is an event which shakes the foundations of ecosystems across the entire planet. The end of the non-avian dinosaurs is one of the more familiar mass extinction events, where species from across different Phyla died out. At the end of the Permian Era, there was an enormous mass extinction which wiped out many plants, vertebrates and invertebrates. One of the saddest losses in this extinction was the enigmatic group of arthropods: the Trilobites. Extinctions can not only wipe out species, but also whole Classes of animals.

From the beginning of the ‘big bang of animals’, the five mass extinction events (shown with the inverted yellow triangles). (Image by Albert Mestre. Public Domain).

The extinction of the Pleistocene megafauna was a little different. There was another variable thrown into the mix. A predator that spread across the globe to colonise almost every continent- Homo sapiens.

Humans as the main driver for megafaunal extinction was advocated by the late Paul Martin for over 5 decades. Martin saw correlation in the extinction of megafauna with the arrival of humans, and proposed his theory of ‘Overkill’. Australian giants like the Diprotodon and Giant Echidna vanished around 50,000-55,000 years ago – around the same time that the earliest evidence of human arrival. The enormous Megatherium and other American giants vanished around 12,000-10,000 years ago – again at around the same time we find evidence for human arrival. Martin proposed quite a picture of humans sweeping across the globe, slaughtering all the mega-fauna in their path.

Some scientists disagreed that little humans could wipe out entire species, genera even, in such a short space of time. Coinciding with the arrival of humans in Australia, American, and even parts of Europe were dramatic changes in the climate. (Indeed these climatic changes may have allowed humans to travel as far as they did so quickly). With changing environments comes extinction of those not able to adapt quickly enough. And a lot of the megafauna were well adapted to their little niche and couldn’t adapt fast enough. For decades there have been two schools of thought: overkill and climate.

The dramatic climatic variations during the Late Pleistocene. From extreme warm periods (interglacials) to much colder periods (glacials). (Image by Hannes Grobe. Public Domain)

Lewis Bartlett and colleagues have recently published their latest research in Ecography which may have the answer. In a prehistoric case of ‘who dun it’, the team have examined the main culprits in incredible detail. They wanted to see if there was a correlation between megafaunal extinction and climate and /or humans. They started by looking at 14 regions across the world and the megafauna that went extinct in these regions. This alone was pretty alarming: 54 out of the 69 Genera of megafauna in South America have become extinct.

Then the hard work began. For each region they gathered an enormous amount of data. Starting at 80,000 years ago, they trawled through the published articles for the latest radiocarbon dates of megafauna. They reconstructed the climate of the past based on latest research in orbital variations, atmospheric gas concentrations, ice sheet extent and sea level change. The arrival of humans was more tricky to pin point in some regions than in others, so the team produced 8 different scenarios based on dates in the literature. (For some regions this date stayed the same for each scenario as the dates were well researched. For others, like Australia and Asia, the dates varied.)

Here’s the sexy science bit. By choosing extinction dates randomly from the publications, they generated 1000 different extinction scenarios. They tested these with different variables to show the results were not just randomly generated. The results were pretty cool. Each of the 1000 scenarios gave a probability. The variable with the highest confidence in the probability was the ‘human arrival and climate lagged’ variable. In short, the simulations with three well researched sets of data across the globe show a strong correlation with the arrival of humans and the extinction of the megafauna. The ‘climate lagged’ is where the climate changed shortly after the arrival of humans, and the researchers acknowledge that climate would have played a part too.

The global spread of Homo sapiens. Compared to other hominin species, humans managed to colonise almost every continent. (Image by NordNordWest. Public Domain)

Is this the nail on the coffin for the debate? Probably not. This is a cool piece of research as it looked at a number of variables, with an enormous amount of data published. The future will bring even more detailed analysis to the table, and the results may well flip. What we do know is that humans did arrive and shortly after many of the big giants became extinct. I personally doubt it was solely down to Martin’s ‘overkill’, but a combination of hunting, climate change, and human made environmental changes.

We admire these Twilight Beasts for their magnificent size (like the iconic mammoth), or their killer instinct (think of Smilodon). Sadly, I think we admire them more because they are gone. Often we forget how beautiful the animals that are still with us are. The splendour of a pride of lions. The elegance of a hippopotamus swimming. The majesty of an eagle soaring high above. We also forget that these amazing animals are survivors of the Pleistocene. Let’s make sure no more megafauna go extinct.

Written by Jan Freedman (@JanFreedman)

Further reading:

Bartlett , L. J., et al. (2015). ‘Robustness despite uncertainty: regional climate data reveal the dominant role of humans in explaining global extinctions of Late Quaternary megafauna.’ Ecography. 38. pp.1-10. [Abstract only]

Helgen, K. M, et al, (2012), ‘Twentieth century occurrence of the Long-Beaked Echidna Zaglossus bruijnii in the Kimberly region of Australia’, ZooKeys, 255, 103-132. [Full article]

Jacobi, R. M. et al. (2009), ‘Revised radiocarbon ages on woolly rhinoceros (Coelodonta antiquitatis) from western central Scotland: significance for timing the extinction of woolly rhinoceros in Britain and the onset on the LGM in Central Scotland’, Quaternary Science Reviews. 28. 2551-56. [Abstract only]

Markoca, A. K. et al. (2013), ‘New data on changes in the European distribution of the mammoth and the woolly rhinoceros during the second half of the Late Pleistocene and the early Holocene’, Quaternary International. 292. 4-14. [Full article]

Martin, P. S. (2005), ‘Twilight of the Mammoths: Ice Age Extinctions and the Rewilding of America’, University of California Press. [Book]

Price, G. (2012), ‘Plio-Pleistocene climate and faunal change in central eastern Australia.’ Episodes-Newsmagazine of the InternationalUnion of Geological Sciences 35. 1  160.

Stuart, A. J. et al. (2002), ‘The latest woolly mammoths (Mammuthus primigenius Blumenbach) in Europe and Asia: a review of the current evidence’, Quaternary Science Reviews. 21. 1559-69. [Full article]

Stuart, A. (2005), ‘The extinction of woolly mammoth (Mammuthus primigenius) and straight-tusked elephant (Palaeoloxodon antiquus) in Europe’, Quaternary International. 126. 171-7. [Abstract only]

Stuart, A.J., Kosintsev, P.A., Higham, T.F.G., Lister, A.M., (2004). ‘Pleistocene to Holocene extinction dynamics in giant deer and woolly mammoth’. Nature 431. 684-689. [Abstract only]