Once upon a time, our world was home to many giants.
Actually, it wasn’t that long ago. After the dinosaurs had done their day, our planet was home to a whole new range of giant animals, from sloths that towered over humans, to woolly mammoths, to giant kangaroos and kangaroos, to magnificent giant geese.
Between 50,000 and 10,000 years ago, nearly 200 of the world’s largest animal species disappeared forever, leaving behind nothing but their large bones (and burrows). It is unclear what ultimately claimed these majestic creatures.
During the time period in which the megafauna disappeared, the world warmed and an ice age ended, suggesting one possible mechanism: climate change. Meanwhile, our species was expanding into new lands, chasing the wealth of resources that came with the retreating ice. And so the debate over the roles of these two possible contributing factors has raged.
Now a new study on the decline of giant herbivorous mammals – the megaherbivores – points the finger at humanity.
Fossils show that, 50,000 years ago, there were at least 57 species of megaherbivores. Today, only 11 remain. They include notable giants such as hippos and giraffes, as well as several species of rhinoceros and elephants, many of which continue to decline.
Such a dramatic decline, the researchers say, is inconsistent with climate change as the sole cause.
“The large and highly selective loss of megafauna over the past 50,000 years is unique over the past 66 million years. Previous periods of climate change did not lead to large, selective extinctions, which argues against a major role for climate in extinctions.” megafauna,” says macroecologist Jens-Christian Svenning of Aarhus University in Denmark
“Another important pattern that argues against a role for climate is that recent megafauna extinctions hit climate-stable areas as hard as unstable areas.”
The new study is a comprehensive review of the evidence available since the extinction of the dinosaurs 66 million years ago. These include the locations and timing of extinctions, habitats and food preferences, estimated population sizes, evidence of human hunting, human population movements, and climate and vegetation records dating back millions of years.
We know that humans coexisted with megafauna, and we have evidence of hunting some species to extinction. We know that our ancestors were capable of hunting large animals effectively.
“Early modern humans were effective hunters of even larger animal species and clearly had the ability to reduce large animal populations,” says Svenning.
“These large animals were and are particularly vulnerable to overexploitation because they have long gestation periods, produce very few offspring at a time, and take many years to reach sexual maturity.”
The new research shows that these human hunters were effective enough to contribute significantly to many extinctions. The megaherbivores, the team found, died out in a variety of climate scenarios in which they had been able to thrive effectively even during times of change. Most of them would have adapted well to a warming environment, the researchers found.
And they died out at different times and at different rates – but all those times were after humans had arrived, or developed the means to hunt them. In fact, the exploitation of mammoths, mastodons, and giant sloths was pretty consistent wherever people went.
Perhaps the reason mammoths hung onto Wrangel Island after the mainland population disappeared was because there were no humans there.
It’s a sobering thought, especially since the megafauna that survive today are dwindling thanks to human exploitation, as a 2019 study found. About 98 percent of endangered megafauna species are at risk of extinction because humans won’t stop eat them.
“Our results highlight the need for active conservation and restoration efforts,” says Svenning. “By reintroducing large mammals, we can help restore ecological balances and support biodiversity, which evolved into ecosystems rich in megafauna.”
No wonder the rest of the animal kingdom fears us.
The research was published in Cambridge Prisms: Extinction.