Wild Brazilian bearded capuchin monkeys (Sapajus libidinosus) use stones to pound open defended food, including cashew nuts. And this activity dates back at least 600 to 700 years, according to a team of scientists led by Dr. Michael Haslam from the University of Oxford, UK.
Archaeological evidence suggests that Brazilian bearded capuchin monkeys have been using stone tools to crack open cashew nuts for at least 600 years. Image credit: University of Oxford.
“Until now, the only archaeological record of pre-modern, non-human animal tool use comes from a study of three chimpanzee sites in Cote d’Ivoire in Africa, where tools were dated to between 4,300 and 1,300 years old,” said Dr. Haslam, lead author of a paper published in the journal Current Biology.
Dr. Haslam and his colleagues observed groups of capuchins at Serra da Capivara National Park in northeast Brazil, and combined this with archaeological data from the same site.
The monkeys use stones as hand-held hammers and anvils to pound open hard foods such as seeds and cashew nuts, with young monkeys learning from older ones how to do the same.
The animals created what the scientists describe as ‘recognizable cashew processing sites,’ leaving stone tools in piles at specific places like the base of cashew trees or on tree branches after use.
The team found that capuchins picked their favorite tools from stones lying around, selecting those most suitable for the task.
Stones used as anvils were over four times heavier than hammer stones, and hammers four times heavier than average natural stones.
The capuchins also chose particular materials, using smooth, hard quartzite stones as hammers, while flat sandstones became anvils.
Using archaeological methods, Dr. Haslam and co-authors excavated a total of 69 stones to see if this tool technology had developed at all over time.
The scientists dug to a depth of 28 inches (0.7 m) at a site close to cashew trees where they had seen modern capuchins frequently using their stone tools.
They identified the tools from inspecting the size and shape of the stones, as well as the distinctive damage on the stone surface caused by capuchin pounding.
Through mass spectrometry, the team was able to confirm that dark-colored residues on the tools were specifically from cashew nuts.
They also carbon-dated charcoal discovered with the stones to establish the oldest tools were least 600 to 700 years old.
According to the scientists, around 100 generations of monkeys have used this tradition of stone tools.
The team also compared tools used by modern capuchins with the oldest excavated examples, finding they are similar in terms of weight and materials chosen.
“This apparent lack of change over hundreds of years suggests monkeys are ‘conservative,’ preferring not to change the technology used, unlike humans living in the same region,” the researchers said.
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Michael Haslam et al. 2016. Pre-Columbian monkey tools. Current Biology 26 (13): pp. R521 – R522; doi: 10.1016/j.cub.2016.05.046
