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Planet Earth

The Monkey at Dawn


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Some time not long before 45 million years ago, a new kind of primate came to be. Known as an anthropoid, it had a face that was flatter than those of the lemur-like primates that existed before. And its descendants--monkeys, apes, and humans--would eventually push these older primates aside. But thanks to a meager fossil record, the question of where this first anthropoid was born has remained open. This past year, vertebrate paleontologists at the Carnegie Museum of Natural History in Pittsburgh and the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing marshaled some impressive evidence for Asia-- rather than Africa--as the home of the ur-monkey.

In 1994 the researchers had discovered a few intriguing teeth of a 45-million-year-old primate near Shanghai that they had rather confidently named Eosimias sinensis (dawn monkey of China). Although the fossils were at least 6 million years older than the next-oldest anthropoid (from Egypt), it was hard to be sure about their true identity. Last April, however, the same team reported finding in the Yellow River valley in central China a relatively complete lower jaw of another species of Eosimias, and in the summer they found an Eosimias anklebone. Eosimias retained molars that cut like scissors--a feature of lower primates--but it also bore the big, daggerlike canines that distinctly mark it as a higher primate. These sorts of traits put Eosimias firmly at the base of the anthropoid family tree.

According to Christopher Beard of Carnegie, the team’s leader, anthropoids may have radiated to the rest of the world, and notably to South America, within a few million years of their Asian dawn. People who believe that anthropoids first evolved in Africa have great difficulty explaining how they went from Africa to South America, says Beard. Most argue that they rafted across the South Atlantic Ocean. Under the Asian origin hypothesis, the only reasonable way of getting monkeys from China to South America is via North America. The good news about that possibility is that the Bering land bridge was always a viable route during the age of mammals.

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