The stones used by Capuchin monkeys in the area of today’s Serra da Capivara National Park in Brazil about 3,000 years ago are already considered as the instruments not used by older humans ever found outside Africa.
In the study, published in Nature Ecology & Evolution, various rounded stones are described due to the blows produced by the capuchin monkeys in the region to break seeds and open nuts. The most interesting fact, however, lies in the fact that these are objects of various shapes belonging to different eras, something that suggests that the monkeys of the region have used stones of different shapes and with a different degree of roundness to scratch or open foods of various hardness over time.
This without considering that it is a fairly detailed individual archaeological record, something that usually belongs to human beings. Not that it was not known that many species of primates already used at the time, or long before, stone tools to facilitate the opening of nuts, but they are the few archaeological sites that can boast of having preserved non-human instruments.
The researchers found more than 1500 stones during excavations and 122 of them showed signs of impact or other changes that clearly indicated that they were used to open nuts or crush seeds, just as different species of monkeys do today. The stones vary in size depending on the period to which they belong. Some, used between 2403 thousand years ago, are low-weight rocks, probably used for smaller or less resistant foods like cashews.
Other stones, used 250 years ago, turn out to be more resistant and heavy rocks, probably used to open harder foods.
“It is the first example of variation in the use of long-term tools outside human lineage,” state researchers Tiago Falótico of the University of Sao Paulo in Brazil and Tomos Proffitt of University College London who performed the study on the stones together with other colleagues.
These changes could be explained by the parallel changes in the availability of different foods over time. For example, cashews, today quite abundant and one of the main foodstuffs for Capuchin monkeys, may not have been so widespread during the past.