Two monkey tooth fossils found in the Tugen Hills of central Kenya in 2006 have shed new light on the species’ evolution.

A team of Yale-affiliated researchers has discovered that the modern monkey, also known as the Old World monkey, was alive approximately three million years earlier than previously thought. The fossil record shows these monkeys from the family Victoriapithecidae died out approximately 12.5 million years ago — however, the teeth found in Kenya are more similar to those of modern monkeys such as baboons and macaques, said study co-author Christopher C. Gilbert, a former Yale postdoctoral researcher and current assistant professor at Hunter College in the City of New York.

The team’s findings, which were published online in the journal PNAS on March 18, are expected to help determine the exact point at which hominoids such as apes and humans diverged from Old World monkeys, said Yale anthropology professor Andrew Hill, one of the project’s leading researchers.

This research will be “a contribution to understanding the origins of the modern fauna of the African bio-geographic region and of the Old World as a whole,” he added.

Hill said the researchers hope to use their discovery to refine what has been known about the ecological and climate conditions driving evolution.

“One thing that some paleontologists are interested in is to work out from the fossil record when major groups of animals diverged from others in the course of evolution,” he said. “This gives us the opportunity to understand the reasons for evolutionary shifts — if we can correlate them with contemporary events, such an environmental or climate change, or the origination of other contemporary animals or plants.”

Other scientists in the field of human evolution said this finding has the potential to shift future research goals. A thorough understanding of evolution comes from comparisons of genomes of living species with their fossil records, which still requires the discovery of more specimens to fill the gaps of the fossil record.

“Figuring out the timing of monkey evolution is one important component of understanding pattern and timing of hominoid [ape and human] evolution,” said David Pilbeam, a professor of human evolution at Harvard University.

The scientists’ next step in their research is to investigate time periods in evolutionary history — such as that between 9.5 and 12.5 million years ago — that were formerly overlooked by researchers.

By identifying the specific specimens that lived in this three million year period and other lesser-known periods, Gilbert said, scientists can reach a more complete understanding of Earth’s inhabitants. He said he hopes his team’s findings will inspire members of the scientific community to look for more rock deposits.

“There is a poor fossil record for the period of time between about 15 and 16 million years ago and [between] eight and nine million years ago. We don’t know much about them,” he said.

The paper’s lead author is James B. Rossie GRD ’03, anthropology professor at Stony Brook University.