Known as Ida (pronounced ?ee-da?), the fossil is thought to represent an early member of the lineage that gave rise to monkeys, apes and humans.
The find is described in a paper published online May 19 in the open-access journal PLoS ONE and also is the subject of a History Channel film, THE LINK, scheduled to premiere Monday, May 25 at 9 p.m., and a book, The Link: Uncovering Our Earliest Ancestor (Little, Brown).
Ida, a young, agile plant-eater, belonged to a previously unknown genus of primate, which the paper's authors have named Darwinius masillae. The fossil is 95 percent complete and includes the skeleton, an outline of the animal's body and the contents of her gut, providing hints to her diet and life history. About the size of a small monkey, Ida lived on fruit and leaves during her short life. Only about nine-months old at death, she may have been overcome by the carbon dioxide gas that blanketed the surface of the volcanic lake where she perished and was preserved until her discovery.
Smith, an associate research scientist at the U-M Museum of Anthropology and an authority on the evolution of mammalian dentition, used CT scans of the fossil to determine Ida's age and life expectancy. "She could have lived as long as 20 years, but she would have been an adult in three to four years," Smith said. "She was probably a third of the way to being an adult when she died."
Ida may help resolve a debate over which group of early primates gave rise to humans. One likely candidate is the tarsioid superfamily, whose modern members are tiny, saucer-eyed forest creatures known as tarsiers. This is the group with which adapoids like Darwinius are now shown to be associated. The other is the lemuroid-lorisoid superfamily, which is evidently more distantly related.
The newly-described fossil shares key anatomical features with higher primates, bolstering the evidence for a link between ancient adapoids and humans, said Gingerich, professor of geological sciences and director of the U-M Museum of Paleontology.
"Darwinius is really a Rosetta Stone of primate evolution because it links many characteristics we haven't been able to associate in one animal before," he said.
In addition to Gingerich and Smith, the paper's authors are Jens Franzen and J