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January 28, 2016

Many large animals in Africa tried grass, but switched diets (Image 1)

A cape buffalo in Kenya's Nakuru National Park.

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A study by researchers at the University of Utah found that as grasses grew more common in Africa, most major mammal groups tried grazing on them at various times during the past 4 million years, but some of the animals went extinct or switched back to browsing on trees and shrubs.

Thure Cerling, a geochemist at the university and first and senior author of the study, says "This is a record of how different mammals responded. And almost all of the mammals did an experiment in eating this new resource: grass." He says things peaked around 2 million years ago.

Today, the only major group that still mostly grazes on grass is bovids, which include cattle, buffalo, sheep, wildebeest, hartebeest and some antelopes such as oryx and waterbucks. However, the study showed that looking at the present does not necessarily reflect the past. While elephants and spiral-horned antelope (elands, kudus and bushbuck) browse on trees and shrubs today, the study showed that 2 million years ago, African elephants grazed on grass and antelopes had mixed diets with lots of grass. Asian elephants, which ate grass and were abundant in Africa 2 million years ago, went extinct in Africa but survive today in Asia, where they graze but also browse on trees and shrubs.

In the study, Cerling and colleagues wrote that the assemblages of grazing, browsing and mixed-diet animals during the past 4 million years "are different from any modern ecosystem in East or Central Africa."

The research also showed there was a much greater diversity of mixed feeders, where they browsed and grazed, in the Turkana Basin of Kenya and Ethiopia from 4.1 million to 2.35 million years ago. From 2.35 million to 1 million years ago, there were many more grazers than there are today, but in the past 1 million years, many grass grazers either switched to browsing trees and shrubs or went extinct, leaving mostly bovids as grazers today.

The study was funded in part by the National Science Foundation (grants DEB 93-10546, IOS 96-04024, EAR 06-17010, BCS 06-21542, DBI 0722598 and EAR 08-19611).

To learn more, see the University of Utah news story 4 million years at Africa's salad bar. (Date image taken: 2015; date originally posted to NSF Multimedia Gallery: Jan. 6, 2016) [Image 1 of 5 related images. See Image 2.]

Credit: Mahala Kephart

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