First Author

Fossils from Ethiopia's Afar valley have shed light on human evolution over the past 6 million years. The dearth of older fossils, however, makes it difficult to corroborate genomic studies suggesting that the gorilla and human lineages diverged between 6 million and 8 million years ago. On page 921, University of Tokyo palaeoanthropologist Gen Suwa and his colleagues report the first fossilized teeth of a large-bodied ape from southern Afar's Chorora Formation. Suwa explains how this new species, which they have named Chororapithecus abyssinicus and dated to roughly 10 million years ago, provides evidence that the human and gorilla lines may have diverged earlier than thought.

You initiated a systematic survey of the Chorora Formation in 2005. Why?

I first visited the Chorora area with my longtime Ethiopian colleagues Berhane Asfaw and Yonas Beyene in 1989. It is 10 million to 11 million years old, and any animal fossil site covering this period would be important to understanding human origins. The area is not fossil-rich, but recent satellite images showed more possible sites. So we decided to do short, systematic surveys every year. An assistant found the canine tooth in 2006 and we found the molars earlier this year.

What is unique about the teeth you found?

The molars of modern gorillas have shearing crests that are specialized for eating leaves and stems; most fossil apes have more generalized molars. The fossil teeth we found are different again, combining shearing crests with thick enamel on one side of the molar —suggesting that this species of ape may have been partially adapted to a fibrous diet.

How has this finding changed your research approach?

We now think apes and very early human ancestors may have lived in more forested environments, and did not get fossilized with other animals. So we are searching in the less obvious patches — with fewer animal bones — in the right geological settings.

Do these teeth redefine the date of the human–gorilla divergence?

We're not yet sure. Until now, there were no convincing fossils to trace the modern African ape between 12 million and 7 million years ago. The ape we describe was either a primitive form of gorilla, or an independent branch showing a similar adaptation at about the time when the gorilla line would have been emerging. We think that currently accepted divergence estimates are unnecessarily biased towards the younger side, and hope we can convince people to be open-minded.