Changing Habitat Killed Off Mega-Herbivores 4.5 Million Years Ago, Not Humans

Dec 17, 2018

An artist's impression of a Hyrachyus, an ancient mega-herbivore and related to present-day rhinos.
Credit University of Utah

Millions of years ago there were diverse and large populations of mega-herbivores, but today there are only a few mega-herbivore species. New research reveals a new theory about the extinction of these ancient mega-herbivore species. 

"A mega-herbivore is a term used by ecologists. It usually refers to big plant eaters that are more than 1,000 kilos in body mass, so we’re talking 2,200 pounds.  In Africa today that would include elephants, giraffes, black and white rhinos and hippos."

That was Tyler Faith, a curator of archeology at the Natural History Museum of Utah and an assistant professor of anthropology at the University of Utah. According to Faith, today’s mega-herbivores are just a shadow of what existed several million years ago.

"For decades now, people have been speculating that our early human ancestors, specifically homo erectus, they played a role in driving some of these large mammals, mega-herbivores to extinction," Faith said. 

But Faith and his collaborators found that early humans are not the reason for the mega-herbivore decline in Africa.

"The timing of this mega-herbivore decline at about 4.5 million years ago, it corresponds with a time when our human ancestors are small bodied, semi-arboreal, frugivores, they’re living in the trees a little bit they can still walk upright on two legs, their diet was more similar to chimpanzees, and they certainly were not hunting large mammals and definitely not to extinction," Faith said. 

Instead Faith and his collaborators found that ecosystem shifts away from forests and increasing grassland expansion lead to the decline of mega-herbivore populations.

"From the fossil teeth of mega-herbivores we can tell what they were eating. Most of the mega-herbivores that are disappearing are animals that ate leaves of trees and shrubs and probably lived in forests," said Faith "So the pattern makes a lot of sense the expansion of grassland habitat and the animals that did not eat grass were disappearing. And it is this long-term steady process that’s really hard to pin on humans, it would be quite far-fetched."