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Earth Matters

Spreading Grasslands — Not Homo erectus — Wiped Out Africa’s Big Animals

June 6th, 2019 by Adam Voiland

Seven million years ago, some truly spectacular creatures roamed the woodlands of East Africa. There was a moose-like giraffe called Shiva’s beast. There were giant buffalo with horns wider than the animals were tall. And the lumbering creatures known as anthracotheres defy easy categorization.

“Whenever I ask colleagues who study anthracotheres how they describe them, they always say: hippo-pig,” laughed Tyler Faith, curator of archaeology at the Natural History Museum of Utah. As for the buffalo: “This was a horn span of 3 meters (10 feet). I mean this was an awesome buffalo.”

Image credit: Slide courtesy of Tyler Faith

These and several dozen variations of more recognizable African megaherbivores — elephants, rhinos, hippos, and giraffes — all went extinct within the past several million years. For decades, archaeologists have pinned the blame on early humans, particularly Homo erectus, a species that emerged 2 million years ago, walked upright, and had a body plan similar to modern humans. Since Homo erectus made stone weapons and was capable of butchering large game, many archaeologists assumed that it hunted Africa’s megaherbivores into extinction — much like the fossil record suggests Homo sapiens (modern humans) did to the large mammals of North and South America some 11,000 years ago.

But nobody rigorously tested whether this “overkill hypothesis” fit with the fossil record. “Speculation had been repeated often enough that it just graduated into fact; it became the truth,” Tyler explained during a recent colloquium at NASA’s Goddard Space Flight Center. To check more rigorously, Tyler and colleagues analyzed fossil assemblages from 101 sites in Eastern Africa.

Image credit: Slide courtesy of Tyler Faith

What they found was a surprise. Megaherbivores began disappearing about 4.6 million years ago — long before Homo erectus came on the scene (1.8 million years ago). And there was no increase in the rate of extinctions even when Homo erectus and butchering showed up in fossil records.

However, when the researchers looked at some key indicators of past environmental conditions, they found one key change — the expansion of grasslands — lined up with the extinctions almost perfectly. Five million years ago, classic open grasslands like today’s Serengeti Plain did not exist in East Africa. Trees and shrubs were a much more dominant part of that African landscape then, explained Tyler.

But as carbon dioxide levels declined, mainly due to orbital variations and changes in the amount of Earth covered by ice, forests retreated and grasslands became dominant. Since many of the megaherbivores fed mainly on woody vegetation, they likely faded away along with their food sources. Meanwhile, other familiar species thrived. The ancestors of wildebeest, hartebeests, Thompson gazelles, oryx, plains zebras, and warthogs — all grazers that live in open habitats — proliferated.

Grasslands dominate northern Tanzania’s Serengeti Plain. The first image shows withered grasslands during a drought. The second image shows the same area during a wetter year. Read more about these images. Credit: NASA Earth Observatory

Faith’s bottom line is that it is time to stop blaming Homo erectus for something they didn’t do. “In the search for ancient hominid impacts on ancient African ecosystems, we must focus our attention on the one species known to be capable of causing them – us, Homo sapiens, over the past 300,000 years,” he said.

Faith’s analysis found that megaherbivore diversity started to decline well before Homo erectus emerged. Image credit: Faith et al.

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6 Responses to “Spreading Grasslands — Not Homo erectus — Wiped Out Africa’s Big Animals”

  1. Heather Renee says:

    Very interesting! Im curious as to how scientists are able to figure out the age of fossils. I mean I get the deeper the older but it’s so crazy to me the way they’ve been able to figure so much out about the history of the earth (& its inhabitants) , the entire universe actually. Just goes to show there are lots of ppl out there WAY smarter than me bc I could never figure out the diff between a million & 4 million year old skull or something.lol

    Anyway, so is this just a hypothesis or has it been proven that this was, in fact the cause for these species dying out so quickly?

  2. Debaditya Bhattacharjee says:

    This was a very interesting and informative article, which I read in its entirety. The graphics were especially intriguing. I assume you calculated a line of best fit from the data points on the scatterplot?

  3. RiHo08 says:

    “But as carbon dioxide levels declined, mainly due to orbital variations and changes in the amount of Earth covered by ice, forests retreated and grasslands became dominant.”

    Do I understand this correctly, that low atmospheric CO2 results in grasslands replacing the flora and fauna abundance of forests? To achieve a verdant, diverse and productive earth, does there need to be more atmospheric CO2 not less for more diversity including forests? Then the question becomes, are those promoting a “Green New Deal” agenda better for earth as a whole? Or is such an agenda, to reduce atmospheric CO2 against earth’s best interests, and, as one of its inhabitants, against man’s best interests as well?

  4. Linda Goudsmit says:

    You will never see this article in the mainstream media because actual environmental science does not comport with the political science that leftists and globalists hawk as “settled science.” The deceitful purpose of blaming man – particularly American men – is the transfer of wealth from industrialized countries to non-industrialized countries for political purposes. It is the biggest lie of the 21st century next to “You can keep your doctor.”

    • JACK AVERY says:

      LUV IT!
      Looking down on North America, earth waves, like ocean waves. show where the last ice age retreated. A buddy in Evanston, WY and I used to discuss (over an adult beverage) the consequences of a 26,000 year wobble in the earth’s rotational travel around the Sun.
      Having spent my teen years on several saltwater fishing boats along the southern California coast, I can see what global overfishing and the introduction of styrofoam did to “my ocean”.

  5. Reg caton says:

    I think this is a well written and informative article. My take from it is there is an optimum level of carbon dioxide in the atmosphere to maintain levels suited for human habitation.
    Too much or too little results in climate extremes either way.

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