South American capuchin monkeys are famous for their careful use of stone as tools to harvest and grind food, a practice that we know has occurred for the last 3000 years.
A new study explains that the type and shape of the tool have changed over time in relation to the food they ate.
A cache of the monkey's stone tools found at a dig site in northeastern Brazil illustrate how different stones were selected to deal with small, soft foods or larger, hard-shelled edibles.
“It’s likely that local vegetation changes after 3,000 years ago led to changes in capuchin stone tools,” says archaeologist Tomos Proffitt of University College London.
Tools respond to climate
The revelation also opens up the possibility that chimpanzees and macaque monkeys, which also use stone tools, may have changed their choice and style of tools, to respond to changes in climate and habitation.
The discovery of the tools is special as archaeological evidence of apes and monkeys tools are uncommon.
The excavation site that revealed the long history of the animals' tool is located in Brazil’s Serra da Capivara National Park. Ancient human tools were also found in the same dig.
Three thousand years of tool evolution
Primatologist Tiago Falótico of the University of São Paulo and Tomos Proffitt of University College London and their colleagues recovered 122 capuchin stone artifacts from four sediment layers. The research team used radiocarbon dating of small wood specimens from each layer to help them form a timeline of the usage of the stones.
Among the inventory of tools were both partial and complete pounding stones, rocks used as platforms on which to pound objects, and pieces of rock that detached from pounding stones and platforms during use. They found that the stone implements dated between 3,000 and 2,500 years old were small and heavy and likely used to smash open small foods like seeds and fruits with soft rinds.
Specific tools for specific nuts
This style of tool lasted for some time until larger pounding stones appeared about 300 years ago. This larger tools likely indicate a shift in the Capuchin diet to harder shelled fruits and nuts that required more force to open.
Tools dated about 100 years old are again smaller and lighter that the research team suspect and were perfect for efficiently opening cashew nuts.
Modern-day Capuchins use similar tools in the area today to open the delicious creamy snack.
The change in tools may be from different populations visiting the site who had different preferences for different stone implements or a single population returned regularly to the site and changed their tool choice to adapt to the changes in the landscape.
“What’s novel is that a stone tool pattern we had already seen in chimps today is now recognizable from the archaeological evidence for capuchins,” says University of Oxford primatologist and archaeologist Susana Carvalho.