The world’s biggest land mammal is the African bush elephant, which can be up to 13 feet tall and 24 feet long. But this elephant — and giraffes, hippos and other large animals — could go extinct because of human activity, leaving the domestic cow as the biggest terrestrial mammal in a couple centuries. In a recent study, researchers scrutinized large mammal extinction as humans spread, and their study is, according to the University of New Mexico, “the first to quantitatively show … that size selective extinction is a hallmark of human activities and not the norm in mammal evolution.”

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Ancient, now-extinct megafauna, or large mammals, like the mammoth, roam the land

Thousands of years ago, the spread of archaic humans from Africa coincided with extinction of megafauna, or large mammals, like sabre-toothed tigers and mammoths, The Guardian reported. “One of the most surprising finds was that 125,000 years ago, the average body size of mammals on Africa was already 50 percent smaller than on other continents,” said Felisa Smith, professor at the University of New Mexico and lead author of the study. “We suspect this means that archaic humans and other hominins had already influenced mammal diversity and body size in the late-Pleistocene.”

Related: The world’s last male northern white rhino has died in Kenya

The researchers compiled extensive data around mammal body size, geographic location, climate and extinction status in the past 125,000 years and modeled diversity and body size distributions for the next 200 years. The study also found that in 65 million years, climate changes didn’t lead to more extinctions. “We suspect that in the past, shifts in climate led to adaptation and movement of animals, not extinction,” said co-author Jonathan Payne of Stanford University. “Of course, today ongoing climate change may result in extinction since most megafauna are limited in how far they can move.”

Smith said we’re really just starting to appreciate megafauna’s crucial roles in ecosystems. “For example, as they walk, their massive size compacts the soil, which can lead to changes in gas exchange or water tables. … We are not entirely sure what the potential loss of these ‘ecosystem engineers’ could lead to,” he said. “I hope we never find out.”

The journal Science published the research this month. Scientists from the University of California, San Diego and University of Nebraska-Lincoln also contributed.

+ University of New Mexico

+ Science

Via The Guardian

Images via Michael Pujals on Unsplash and the University of New Mexico