Once upon a time, our world was home to many giants.
Actually, it wasn’t that long ago. Once the dinosaurs had their day, our planet was home to a whole new range of giant animals, from sloths that towered over humans, to woolly mammoths, giant wombats and kangaroos to magnificent giga-geese.
About 50,000 to 10,000 years ago, nearly 200 of the world’s largest animal species disappeared forever, leaving nothing but their huge bones (and burrows). It is not clear what these magnificent creatures ultimately claimed.
During the time frame in which the megafauna disappeared, the world warmed and the Ice Age ended, suggesting one potential mechanism: climate change. Meanwhile, our own species expanded into new lands, chasing the wealth of resources that came with the retreating ice. And so the debate raged about the roles of these two potentially contributing factors.
Now, a new study on the decline of giant herbivorous mammals – the megaherbivores – is pointing the finger at humanity.
Fossils show that at least 57 species of megaherbivores existed 50,000 years ago. Today, only 11 remain. These include remarkable monsters such as hippos and giraffes, as well as several species of rhinoceros and elephants, many of which are still in decline.
Researchers say such a dramatic decline is inconsistent with climate change being the sole cause.
“The large and highly selective decline of megafauna in the last 50,000 years is unique in the last 66 million years. Previous periods of climate change did not lead to large, selective extinctions, which argues against a major role of climate in the extinction of megafauna,” says macroecologist Jens-Christian Svenning from Aarhus universities in Denmark
“Another significant 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 consists of a comprehensive review of the available evidence since the extinction of the dinosaurs 66 million years ago. These include sites and timing of extinctions, habitat and food preferences, estimated population size, evidence of human hunting, human population movements, and climate and vegetation data going back millions of years.
We know that humans coexisted with megafauna, and we have evidence that some species were hunted to extinction. We know that our ancestors were able to effectively hunt large animals.
“Early modern humans were efficient hunters of even the largest animal species and clearly had the ability to reduce populations of large animals,” 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.”
New research shows that these human hunters were efficient enough to have contributed significantly to many extinctions. The megaherbivores, the team found, died out in a variety of climate scenarios in which they were able to effectively thrive even in times of change. Most of them would adapt well to a warming environment, the researchers found.
And they died at different times and at different rates—but all those times were after humans arrived or developed the means to hunt them. In fact, the use of mammoths, mastodons, and giant sloths was pretty consistent wherever humans went.
Perhaps the reason the mammoths stayed on Wrangel Island after the mainland population disappeared was because there were no people there.
It’s a sobering thought, especially since the megafauna that survive today are dwindling due to human exploitation, a 2019 study found. About 98 percent of endangered megafauna species are at risk of extinction because humans won’t stop eating them.
“Our results highlight the need for active conservation and restoration efforts,” says Svenning. “By reintroducing large mammals, we can help restore ecological balance and support the biodiversity that has evolved in megafauna-rich ecosystems.”
No wonder the rest of the animal kingdom fears us.
The research was published in Cambridge Prisms: The Demise.