for National Geographic News
A ten-million-year-old jawbone recently unearthed in Kenya may have come from the last common ancestor of gorillas, chimpanzees, and humans, researchers say.
The find also helps refute a theory that the apes that eventually gave rise to humans left Africa for Asia and Europe, only to return much later, as many experts have hypothesized.
The jaw was found at Nakali, Kenya, on the eastern edge of the Great Rift Valley, along with incisor, canine, and molar teeth.
The teeth are so different from previous finds that researchers placed the creature, named Nakalipithecus nakayamai, in a new hominid genus.
Hominids are part of a broad family of primates that includes Africa's chimpanzees and gorillas and Southeast Asia's orangutans. The group also includes our own genus, Homo, and the extinct Australopithecus.
Scientists estimate that orangutans split off from the lineage that ultimately led to humans about 12 million years ago. Gorillas and chimps are believed to have parted ways from our ancestors about eight and four million years ago, respectively.
"We think that the new ape ... is very close to the common ancestor of gorillas and chimpanzees and humans," said Yutaka Kunimatsu, an assistant professor at the Primate Research Institute at Kyoto University and co-leader of the joint Kenyan-Japanese team that found the fossil.
The findings appear in this week's issue of the journal Proceedings of the National Academy of Sciences.
The newfound teeth are about the size of a modern female gorilla's and show indications of a mostly vegetarian diet.
"The animal had thick enamel on its cheek teeth ... so we think that the new ape ate a considerable amount of hard food, probably nuts and seeds," Kunimatsu said. "It probably also ate other food, like most primates."
When Nakalipithecus was alive, Kunimatsu said, a few grassland clearings would have dotted a mostly forested region.
SOURCES AND RELATED WEB SITES