SALT LAKE CITY, April 4 (UPI) -- Fossil teeth of African animals show in the past 10 million years different plant-eaters switched diets from leaves and shrubs to grass, U.S. researchers say.
Scientists are the University of Utah say different species made the grazing switch at different periods in response to climate change, a university release said Monday.
The first animals to "hit the hay" -- technically warm-season grasses known as C4 plants -- were zebras' ancestors, starting 9.9 million years ago, the fossil study found.
Next, some but not all, rhinos made the switch at 9.6 million years ago, and grass-grazing spread 7.4 million years ago to the ancestors of elephants, while hippos began grazing on grass more slowly.
And giraffes, with their heads in the trees, never gave up the salad bar, the research found.
"This record is the first to illustrate the dietary response among herbivore families to the appearance of warm-season grasses in East Africa" at least 10 million years ago, study author Kevin Uno, a doctoral student in geology, said. "Grass is now the main food for many herbivores there."
The findings "demonstrate that different animals respond differently to ecological change," said Utah geochemist Thure Cerling.
Climate changes have the potential to transform a forest into grassland or vice versa, the researchers said, and animals must change their diets or suffer the consequences, which in extreme cases might mean moving to a new habitat or eventually going extinct.
