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GSloths, musk oxen, and short-nosed kangaroos: they’ve all gone the way of the dodo, vanishing from the face of the earth. These are just a few of the large mammals that are no more. Of the 57 species of megaherbivores known to have lived 50,000 years ago, only 11 survive. That’s a grim 81 percent extinction rate.
Defined as large land mammals with an average adult body mass of 2,200 pounds or more, today’s remaining megaherbivores include elephants, rhinos, giraffes, and hippos. These animals play a critical role in their ecosystems, from seed dispersal to landscape management.
Elephants, for example, reduce the density of trees and shrubs through their movement and feeding habits. These open spaces make way for plains animals such as antelope and zebra, while the hollows and crevices formed by broken branches and felled trees create habitats for small mammals, insects and fungi.
But these large creatures, unable to hide under a log or move with the agility of a gazelle, were particularly amenable to early humans looking to get the most out of every hunt. If you’re looking for meat to fill your belly and a fur to keep your family warm, a woolly mammoth has a lot more to offer than a hare.
“We know that prehistoric humans were very focused on hunting large species,” says Jens-Christian Svenning, director of the Danish National Research Foundation’s Center for Ecological Dynamics in a Novel Biosphere at Aarhus University. He is also the lead author of a recent paper published in Cambridge Prisms: Extinction who argues that it was not climate change but human hunting that caused the extinction of most megaherbivores over the past 50,000 years.
A woolly mammoth has much more to offer than a hare.
To reach their conclusions, Svenning and his team analyzed ancient data on extinctions, climate, and human migration that had been collected over the past six decades. The work continues a conversation that began in earnest in 1966 when an American paleontologist named Paul Schultz Martin first put forward his overkill hypothesis, suggesting that migrating humans preyed on North American megafauna from the Pleistocene up until the extinction event. A few years ago, researchers published a paper in Nature who also concluded that the distribution of megafauna through time and space in prehistoric South America closely matches human demographic data and the discovery of spear points, so-called fish tails, in archaeological finds.
“It’s a long-term discussion,” says Svenning, who argues that improvements in survey techniques and data quality over the past few decades have brought us closer to a definitive answer to the question of what happened to the megafauna. “We have a much better understanding now than we did in the 1960s,” he says. “What we’ve done is reassessed all of this data, and it allows us to say that we can totally rule out that climate played a major role in this kind of extinction.”
The data the researchers collected and analyzed show that the locations and timing of extinctions do not match global patterns of climate change. However, they do correspond closely to patterns of human colonization, which occurred during or after our arrival at many different times and places around the world.
“We conclude that it is one of the strongest, most consistent patterns we have in ecology,” Svenning says. His team’s findings indicate that these patterns of megafauna extinction began when humans first migrated out of Africa, about 100,000 years ago. The extinctions accelerated about 50,000 years ago as Eurasia and Australia were colonized by humans hunting big game.
Ending up on the end of a spear had such a big impact on large mammals because they naturally have a slow replacement rate. The gestation period is long, and so is the maturation process. The 46 species of megaherbivores that have disappeared in history simply couldn’t reproduce fast enough to replace the human deaths.
Felisa Smith, a paleoecologist and professor at the University of New Mexico, believes that the human impact on the megafauna extinction is no longer in dispute. “I think the work of the last few decades has shown pretty convincingly that humans played a pretty substantial role in the extinction,” Smith says.
This is not about assigning blame, says Svenning. “People who lived thousands of years ago never had access to the full picture. These things were happening on long timescales and large spatial scales that no one had an overview of; whatever people did, it was hard to see the consequences. And of course, people just had to survive as best they could.”
Svenning hopes readers will gain a greater understanding of the relationships between humans, megafauna and the natural world. Large mammals are still highly vulnerable to extinction, with more than half of the existing species weighing more than 22 pounds listed as vulnerable, endangered or critically endangered by the International Union for Conservation of Nature. “When we restore forests, we can’t just think about the trees,” he says. “We have to think about the animals that live there.” 
Main image: maradon 333 / Shutterstock
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