Scientists in Africa have unearthed the remains of six new species of large prehistoric mammals, including an ancestor of elephants and a 5,000-pound rhinoceros-like beast that roamed Ethiopia's highlands 27 million years ago.The discoveries offer new clues to the fate of Africa's mammals during the "dark period" in the interval between 32 million years ago and the time 8 million years later when the prehistoric continent known as Afro-Arabia began to connect with Eurasia. It was only after that contact that Africa developed the spectacular mix of lions, tigers, hippos, hyenas, antelopes and elands for which it is famous today. All of these animals evolved from Eurasian immigrants who crossed the frontier when the continents joined. Before that happened, Africa had evolved an array of mammals all its own, among them rodents, primates and some larger species, thought to include several elephant-like animals and other plant-eaters. Before the Ethiopian discoveries, however, none was believed to be larger than a modern-day Texas longhorn steer. "Eight million years is a very long period not to know anything about an entire continent," said John Kappelman, a paleontologist at the University of Texas at Austin who led the multinational team that has worked in Ethiopia's northwestern Chilga region since 1997. "People have been looking for rocks of this age for a long time." Results of the explorations were reported today in the journal Nature.
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