Wild capuchin monkeys have been making stone tools for at least 3,000 years, and their technology has changed over this time, suggests a study published online this week in Nature Ecology & Evolution.
Monkeys, chimpanzees and otters are all known to use stones in the wild to crack open nuts and shells. However, until now, chimpanzees were the only non-human animal with a known archaeological record.
Tomos Proffitt and colleagues excavated a capuchin archaeological site in Brazil, where monkeys today use stones to crack open cashew nuts. Using radiocarbon dating and stone-tool analysis, the authors found that the monkeys may have been doing this for 3,000 years (or 450 generations). They also suggest that the monkeys have changed their methods over time. During the earliest phase at the site, which began 3,000 years ago, monkeys used smaller and lighter stone tools. From 2,500 to 300 years ago, the capuchins using bigger and heavier stones to process foods. They then reverted to slightly smaller tools in the most recent period, which is associated with the cashew-processing of today.
The authors suggest that the changes in tools used may be explained by several theories: different capuchin groups could have used different stones; or that before cashews became more available, different foods could have required different sized tools for processing.