for National Geographic News
Researchers have found the first reported chimpanzee fossils in Kenya's Rift Valley, providing the first physical evidence that chimpanzees coexisted with early human ancestors, known as hominins.
Thousands of fossils, including the famous Australopithicus afarensis, "Lucy," found in Ethiopia, have been filling in the hominin family tree. Early humans split off from a common ancestor shared with chimpanzees between five and eight million years ago. (See "Chimps, Humans 96 Percent the Same, Gene Study Finds.")
"But on the chimpanzee side we've had nothing," said Nina Jablonski, curator of anthropology at the California Academy of Sciences in San Francisco.
Jablonski identified at least three fossil chimpanzee teeth from a set of fossils collected by University of Connecticut anthropologist Sally McBrearty. The two scientists report their discovery in tomorrow's issue of the science journal Nature.
McBrearty uncovered the fossils in the Kapthurin Formation, a section of the Rift Valley near Kenya's Lake Baringo.
She and other researchers had previously found Homo erectus and Homo rhodesiensis fossils in the same geologic layer. This overlap suggests that the early human species and the newly found chimpanzee shared the same turf during the Middle Pleistocene, about 780,000 to 130,000 years ago.
Three teetha molar and two incisorslikely came from the same individual, a chimpanzee living about 545,000 years ago.
"The information is straightforward and very compelling," said William Sanders, a paleontologist at the University of Michigan's Museum of Paleontology. "It would be great to have more."
"As tantalizing as it is, it's really frustrating because it shows us how poor the chimpanzee fossil record is," he said.
Finding the Fossils
McBrearty unearthed the teeth early last summer on a routine walk through her research area in the Kapthurin Formation, where she's been working for more than a decade.
She then moved the fossils to the National Museums of Kenya in Nairobi. All archeological evidence found in the country is stored in the museums' vaults.
SOURCES AND RELATED WEB SITES