The fossil was discovered by amateur fossil hunters in 1983 in a mile-wide crater called the Messel Shale Pit, not far from Frankfurt. Scientists speculate that at one time the pit was a volcanic caldera, where animals got caught and their remains unusually were well preserved. The amateurs saw that they had a very good fossil, but they did not recognize its potential importance.
The location, a UNESCO World Heritage Site, has been the source of many other fossils from the Eocene Period, about 50 million years ago.
The fossil was shown by collectors to Dr. Hurum, who brought in colleagues from Oslo and from the Senckenberg Research Institute to authenticate the find. They bought the specimen so that it would not disappear into private hands.
Examination of the fossil went on for two years. They have called the specimen Darwinius masillae. The researchers were able to keep their work secret until word leaked out last week.
Hurum's team said 95 percent of the fossil's skeleton appears intact. It has a long, curling tail. X-rays show it was young; probably about nine months in age. It had baby teeth and, beneath them, adult teeth forming to replace them. There also was evidence that the animal had once broken its wrist.
It is hard to say what the find may do to the modern understanding of evolution. The fossil, for one thing, is far older than any of the human ancestors other scientists have reported finding in what is now eastern Africa. "Lucy," probably the best-known African fossil that is generally accepted as pre-human, is somewhat more than 3 million years old.
"Ida" is also different in many ways from later animals, said Holly Smith of the University of Michigan, who was brought in to examine the fossil's teeth for clues to its development. For one thing, Smith said, the fossil had all its baby teeth, and all its adult teeth as well. Modern children lose their front baby teeth around age 6, but molars in the back of the jaw do not develop for several more years.
"This whole species grew up fast," Smith said. "You wouldn't find that in a great ape or in a human."
The fossil, encased in plastic, was shown to reporters. It will be returned to Oslo. A plaster cast will go on display at the Natural History museum in New York.
"This discovery represents both great minds and a great find," said Ellen Futter, president of the museum.