As grasses grew more common in Africa, most major mammal groups tried grazing on them at times during the past 4 million years, but some of the animals went extinct or switched back to browsing on trees and shrubs, according to a study led by the University of Utah.
"It's as if in a city, there was a whole new genre of restaurant to try," says geochemist Thure Cerling, first and senior author of the study published today by the journal Proceedings of the National Academy of Sciences. "This is a record of how different mammals responded. And almost all of the mammals did an experiment in eating this new resource: grass."
The experiment peaked about 2 million years ago, says Cerling, a distinguished professor of geology and geophysics. The only major group that still mostly grazes grass is the bovids: cattle, buffalo, sheep, wildebeest, hartebeest and some antelopes such as oryx and waterbucks.
The study also revealed that the present isn't necessarily the key to the past in terms of what animals eat. Today, elephants and spiral-horned antelope (elands, kudus and bushbuck) browse on trees and shrubs, but the study showed that 2 million years ago, African elephants grazed on grass and the antelopes had mixed diets with a lot of grass. Asian elephants, which ate grass and were abundant in Africa 2 million years ago, went extinct in Africa but survive in Asia, where they graze but also browse trees and shrubs.
"That the diet of some of these animals is different from that of the present was a surprise, and shows the importance of challenging one's assumptions when making ecological reconstructions," says study co-author and geologist Frank Brown, dean of the University of Utah's College of Mines and Earth Sciences.
Overall, 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."
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