What killed off prehistoric elephants and their relatives?

There have been conflicting theories about what led to the extinction of mastodons and other elephants. One hypothesis is that prehistoric elephants and other mammalian megafauna were wiped out by the ravenous hunting of early humans as we spread across the globe. 

But now, a new study from the University of Bristol supports an entirely different conclusion. In collaboration with paleontologists at the Universities of Alcalá and Helsinki, the team carried out the most complex analysis to date on the rise and decline of elephants. 

The research delved into the evolution of 185 species over 60 million years by studying museum collections all over the world. 

“Most proboscideans over this time were nondescript herbivores ranging from the size of a pug to that of a boar. A few species got as big as a hippo, yet these lineages were evolutionary dead-ends. They all bore little resemblance to elephants,” explained study co-author Dr. Zhang Hanwen.

Roughly 20 million years ago, when the Asian and African continents collided, proboscidean (elephant) evolution took a turn, by allowing ancestral elephants new areas to explore in Eurasia. Once out of Africa, the elephants evolved 25 times faster than their slowly evolving African ancestors. This led to a boom in elephant and elephant-like species in Eurasia. 

However, this boom wasn’t to last. The rapidly changing climate demanded changes just as quick in the evolution of creatures that were to survive. 

By 2.4 million years ago, extinction of prehistoric elephants and their relatives had peaked in Africa. Eurasia and the Americas soon followed at 160,000 and 75,000 years ago, respectively. 

These extinction time periods might let our ancestors off the hook – they don’t correlate with human expansions. Instead, it looks like climate may be the culprit. This isn’t to say that humans played no role, they certainly still hunted mastodons and other prehistoric elephants, they just may not be the main cause of extinction.    

“We didn’t foresee this result. It appears as if the broad global pattern of proboscidean extinctions in recent geological history could be reproduced without accounting for impacts of early human diasporas. Conservatively, our data refutes some recent claims regarding the role of archaic humans in wiping out prehistoric elephants, ever since big game hunting became a crucial part of our ancestors’ subsistence strategy around 1.5 million years ago,” said study co-author Dr. Zhang Hanwen.

“Although this isn’t to say we conclusively disproved any human involvement. In our scenario, modern humans settled on each landmass after proboscidean extinction risk had already escalated. An ingenious, highly adaptable social predator like our species could be the perfect black swan occurrence to deliver the coup de grâce.”

The study is published in the journal Nature Ecology and Evolution.

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By Zach Fitzner, Earth.com Staff Writer