ScienceDaily (Apr. 5, 2011) — Fossil teeth of African animals show that during the past 10 million years, different plant-eating critters began grazing on grass at different times as many switched from a salad-bar diet of tree leaves and shrubs, says a University of Utah study.
The chewing surface of a fossilized upper molar from an equid -- an ancestor of zebras -- that lived in East Africa 9.6 million years ago. University of Utah researchers studied 452 fossil teeth from nine families of animals to show that between 10 million and 3 million years ago, different East African plant eaters changed at different times from a diet of trees and shrubs to a diet of warm-season grasses. (Credit: Kevin Uno, University of Utah)
The first animals to hit the hay -- technically warm-season grasses known as C4 plants -- were zebras' ancestors, starting 9.9 million years ago. Next, some but not all rhinos made the switch, beginning 9.6 million years ago. Grass-grazing spread 7.4 million years ago to the ancestors of elephants. Hippos began grazing on grass more slowly. And giraffes, with heads in the trees, never left the salad bar.
The study -- by a Utah-led international team of researchers -- is being published online in the journal Proceedings of the National Academy of Sciences.
It constructed a 7-million-year record of dietary change -- from 10 million to 3 million years ago -- by analyzing carbon isotope ratios in 452 fossilized teeth from nine animal families living at three sites in Kenya also occupied by ape-like human ancestors.
"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, says the study's first author, Kevin Uno, a doctoral student in geology at the University of Utah. "Grass is now the main food for many herbivores there."
He adds: "The results paint a picture of differential dietary response to changes in climate and landscape from 10 million to 3 million years ago, a period that includes the appearance of hominids that eventually gave rise to humans."
The findings "demonstrate that different animals respond differently to ecological change," says geochemist Thure Cerling, the study's senior author and a distinguished professor of geology and geophysics, and biology at the University of Utah.
"This has implications for the future of our planet as climate and ecology change as a result of human activities -- not only climate change, but land-use change such as agriculture and desertification," he adds. "And it is not always possible to predict how different parts of the ecosystem will respond to any of these changes."
Uno and Cerling did the study with John Harris of the George C. Page Museum in Los Angeles; paleontologist Meave Leakey of Kenya's Turkana Basin Institute based at Stony Brook University in New York; and Japanese scientists Yutaka Kunimatsu and Masato Nakatsukasa of Kyoto University, and Hideo Nakaya of Kagoshima University.
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Late Miocene to Pliocene carbon isotope record of differential diet change among East African herbivores
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