Washington, Feb 18 (Xinhua) Researchers have found evidence that West African chimpanzees used stone tools to crack nuts 4,300 years ago, pushing chimpanzee tool use back thousands of years and indicating Chimpanzees also have their own Stone Age, according to a recent research published in the journal Proceedings of the National Academy of Sciences.

The international team, led by Julio Mercader, Department of Archaeology, University of Calgary, Canada, suggests that chimpanzees developed this behaviour on their own or inherited the trait from a common ancestor with humans.

Chimpanzees were first observed using stone tools in the 19th century. Julio Mercader and colleagues found stone tools at the Noulo site in Ivory Coast, the only known prehistoric chimpanzee settlement. The excavated stones showed the hallmarks of use as tools for smashing nuts when compared with ancient human or modern chimpanzee stone tools.

Also, several types of starch grains were found on the stones, which the researchers say is residue derived from cracking local nuts.

The tools were found to be 4,300 years old, which, in human terms, corresponds to the later Stone Age and was before the advent of agriculture.

The researchers say these findings add further support to the current body of evidence showing that chimpanzees transmit cultural information. This type of tool use could have originated with an ancestor common with humans, instead of arising independently among hominins and chimpanzees or through imitation of humans.