LOS ANGELES AND NEW YORK — A 47-million-year-old primate fossil that is so complete scientists can even tell what the animal's last meal was promises to shed new light on the earliest stages of evolution of the lineage that eventually led to humans, researchers said Tuesday.
The unprecedented fossil of a lemur-like creature that probably weighed no more than 2 pounds when it was fully grown is remarkable because it is the most complete primate specimen ever obtained.
For the most part, the story of primate evolution has been pieced together from fossilized skulls, jawbones and the occasional foot -- leaving large gaps in anatomy for researchers to fill in with informed speculation.
"This fossil is so complete . . . it is unheard of in the primate record," said paleontologist Jorn H. Hurum of the University of Oslo. "You have to get to a human burial to see something this complete."
Hurum is the lead author of a paper that appeared Tuesday in the online journal PLoS One as part of a massive publicity campaign. The same day, the information about the primate was revealed at a Hollywood premiere-like news conference at the American Museum of Natural History in New York, where a replica of the fossil is now on display. Even New York Mayor Michael R. Bloomberg showed up for the event.
A book about the discovery, called "The Link," will be published today by Little Brown and Co., and a documentary with the same name will air Monday on the History Channel.
Asked about the unusual amount of hype surrounding the announcement, Hurum was unrepentant. "That's part of getting science out to the public, to get attention," he said. "I don't think that is so wrong."
As is evident from the title of the book and documentary, the fossil is being promoted as a kind of "missing link" in the evolution of humans. But the researchers themselves are more circumspect.
"It is a representative of an ancestral group giving rise to all kinds of higher primates," Hurum said. "We are not dealing with our great-great-great-grandmother but perhaps our great-great-great-aunt."
But critics say it's not even that closely related.
"It's more like our third cousin twice removed," said paleontologist Chris Beard of the Carnegie Museum of Natural History at Johns Hopkins University. "It's part of the primate family tree that is about as far away from humans as you can get and still be a primate."
Regardless of the circus-like publicity and controversy over the researchers' interpretations, the fossil is certainly a gem.
It is "the most completely preserved fossil primate that has ever been found," said paleontologist Tim White of UC Berkeley, who was not involved in the research. "It preserves things that are almost never preserved -- stomach contents, tissues, hair. That only happens in very unique circumstances."
In this case, the unique circumstance is the Messel Shale Pit, a world-renowned fossil source in Germany about 25 miles southeast of Frankfurt. Formed by a volcanic eruption nearly 48 million years ago, the shale in the pit has yielded a bounty of fossils from the Eocene epoch, when that region of Germany was a tropical forest.
Animals that fell into the volcanic lake sank to the bottom and lay virtually undisturbed until the present. The cocktail of minerals in the water and sediment contributed to preservation.
"Other mammals have been found there with hair, stomach contents and other features," White said. "People had always hoped that a primate would come out."
The fossil, formally called Darwinius masillae but nicknamed Ida after Hurum's daughter, was found by amateur fossil hunters in 1983, a period when excavations were hurried because of plans, since aborted, to turn the depleted oil shale mine into a garbage dump.
Ida was broken in half and the lower portion was sold to the Wyoming Dinosaur Center. The top remained in a private collection out of the reach of scientists until two years ago, when it was offered to the Natural History Museum at the University of Oslo for $1 million. After negotiations, it was purchased for "substantially less," Hurum said. The university borrowed the bottom half from the dinosaur center.
At that point, researchers quickly realized that the two parts comprised virtually the entire animal. All that is missing is part of the left leg, broken off at the knee, probably when the fossil was collected.
Ida was about 23 inches long from the tip of her nose to the tip of her tail, "like a small cat in size," Hurum said. She was an adolescent, about 9 months old. The absence of a baculum, or penis bone, indicates she was female.
The bones are extremely fragile and cannot be studied individually, but the specimen was studied intensively with X-rays and computed tomography.
Ida has opposable thumbs, which places her squarely in the primate family. She also has fingernails -- not claws as would be expected from a more primitive animal. The talus, or ankle bone, is identical to that in humans, but smaller.