WASHINGTON, D.C. AND LEIPZIG, GERMANY - Chimpanzees in a remote West African rainforest use stones and branches as hammers to crack open different types of nuts when foraging. While the nuts they crack are available throughout tropical Africa, this nut-cracking behavior has been documented only among chimpanzees from western Côte d'Ivoire, Liberia and southern Guinea-Conakry.
How old is this behavior? Have nut-cracking techniques changed over time? To answer these questions, a unique collaboration of scientists - Christophe Boesch, an expert in chimpanzee behavior of the Max Planck Institute for Evolutionary Anthropology in Germany, Julio Mercader, a specialist in rainforest archaeology in The George Washington University Department of Anthropology, and Melissa Panger, who studies primate tool use at GW - launched an archaeological excavation of a chimpanzee nut-cracking site in Côte d'Ivoire's Tai National Park in September 2001.
Using archaeological methods on a non-human species for the first time, the excavations revealed new facets and confirmed others of chimpanzee tool behavior. Chimpanzees at the site known as "Panda 100," for example, collect rocks from various sources across the landscape and bring them to nut-cracking sites.
The repeated occupation of the same site over many seasons allowed for the cracked nut shells and stone pieces that break off of the hammers to build up. The unearthed materials include more than 479 stone pieces that may have flaked off when smashed on tree roots the chimpanzees used as anvils.
In addition to the possibility of tracing ape culture back in time, the scientists also believe the research will open up new ways of interpreting some early hominid, or human, sites.
"Some of the stone by-products of chimpanzee nut-cracking are similar to what we see left behind by some of our early ancestors in East Africa during a period called the 'Oldowan,'" said Mercader, the lead author of the journal article "Excavation of a Chimpanzee Stone Tool Site in the African Rainforest" that will appear in the May 24 edition of Science.
The results of the team's research indicates the possibility that some of the technologically simplest Oldowan sites could be re-interpreted as nut-cracking sites and that some artifacts from the more sophisticated Oldowan assemblages could be proof of hard-object feeding by hominids.
"We know that flaked stone tools were used 2.5 million years ago, but stone tools may have been used by hominids as long as 5 million years ago," said Panger, a coauthor on the article along with Mercader and Boesch. "If we look for assemblages of stone pieces like those we have found left behind by the chimpanzees, we can infer that those assemblages may relate to tool use, even if we don't have the tools."
Until now, archaeologists have focused on buried cultural remains left behind by our ancestors, but with the excavation of the chimpanzee stone tool site, scientists now know that humans are not the only animals whose behavior creates archaeological sites. This discovery opens up a new territory for archaeology, primatology, and paleoanthropology.
The data also highlights how much more can still be learned about our closest living relative, the chimpanzee, to understand humanity's uniqueness.
The project was primarily supported by the Max-Planck Institute of Evolutionary Anthropology. Additional funding was received from The George Washington University, National Geographic Society, and the National Science Foundation.
A press conference to discuss the study will be held on Thursday, May 23, at 1 p.m., at The George Washington University (Marvin Center, Room 309, 800 21st Street, N.W., Washington, D.C.). Media wishing to attend the press conference should contact Bob Ludwig at 202-994-3566.
For information on obtaining rights for using photographs pertaining to the study, please contact the authors, Christophe Boesche at boesch@eva.mpg.de or Julio Mercader at madrid@gwu.edu. Additional information can be obtained from: Wild Chimpanzee Foundation at http://www.wildchimps.org and the Max Planck Institute for Evolutionary Anthropology at http://www.eva.mpg.de/primat
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