The atomic bomb, the plastic dumping ground we call our oceans, and Psy's Gangnam Style – the human race has a lot to answer for, but according to a study recently published in the journal Science, the extinction of Africa's large mammals during the Plio-Pleistocene period is not one of them.
When our hominin ancestor "Lucy" (Australopithecus afarensis) meandered the African plains (specifically, the area around Hadar, Ethiopia) 3 million years ago, she would have met at least three species of giraffe, two species of rhino, a hippo, and four species of elephant-like animals. Today, the vast majority of these large, plant-eating mammals are resigned to the history books. Scientists are not exactly sure when or why they faced extinction but the blame is usually placed on our hominin relatives.
However, scientists from the University of Utah say this could be wrong. According to the team's research, the timeline simply doesn't fit.
"Our analyses show that there is a steady, long-term decline of megaherbivore diversity beginning around 4.6 million years ago," lead author Tyler Faith, curator of archaeology at the Natural History Museum of Utah and assistant professor in the Department of Anthropology at the University of Utah, said in a statement.
"This extinction process kicks in over a million years before the very earliest evidence for human ancestors making tools or butchering animal carcasses and well before the appearance of any hominin species realistically capable of hunting them, like Homo erectus."
So, if not us, who (or what) is responsible for their demise? Climate change is the number one suspect. Specifically, the researchers believe the extinctions were the result of falling carbon dioxide levels in the atmosphere, which triggered the expanse of grassland at the expense of shrubland.
The team came to this conclusion after analyzing more than 100 fossil assemblages from the last 7 million years, comparing the results to stable carbon isotope records of vegetation structure and herbivore teeth, and independent records on climatic and environmental trends. They found that over the last 7 million years, 28 lineages of megaherbivore species have gone extinct. What's more, additional analysis suggests that this decline in diversity started roughly 4.6 million years ago.