Capuchin monkeys at the Serra da Capivara National Park in Brazil have been using stone tools for 3,000 years, leaving behind a valuable archaeological record.

When archaeologists took a closer look at the different tools of Brazil's capuchin monkeys in the span of three millennia, they found that there are notable variations in size, design, and method of use over time.

Archaeologists have long known that the use of tools are not exclusive to humans, but this is the first time they've been able to study non-human tools to trace the changes in the behavior of another species through time. Chimpanzees have been using tools for around the same number of years as capuchin monkeys, but chimpanzee tools haven't changed significantly at all.

Capuchin Monkey Tools Through The Years

In the study published in the journal Nature Ecology & Evolution, archaeologists observe the changes in the tools to track the changes in capuchin monkey diet and behavior.

The oldest stone hammers from 3,000 to 2,400 years ago were found to be smaller, lighter, and more battered than modern capuchin monkey tools. According to the scientists, a likely explanation is that the monkeys were eating smaller, less hardy foods such as seeds. Smaller food mean that it's more likely for the capuchin monkeys to miss their target, making their tools more banged up.

The next stone tools recovered are from 640 to 565 years ago, with archaeologists unearthing many anvils alongside the stone hammers. The hammers from this period are larger and heavier than modern tools, which indicates that capuchin monkeys moved on from eating seeds to food that's even harder than the cashews they eat today.

Finally, the newest tools recovered from the last century are found with round quartzite cobbles along with conical marks on the flattest part of the surface. A number of the tools even have cashew residue on them, which made it easy to identify what these newer hammers were used for.

Study author and archaeologist Tomos Proffitt of University College London explained that their findings point to two possible scenarios. One possibility is that different capuchin populations lived in the same site at various periods, with each population using a particular type of stone tool on their preferred food. Another is that a single population lived in the site and changed their tools over the years to adapt to the food available.

What Does This Mean?

The study authors noted that although the capuchin monkey tools shift over time, their use of these tools do not change at all: percussion. All of their tools are variations of a stone hammer, whereas humans evolved to use tools in different ways, such as moving from smashing food with rocks to shaping sharp edges on these rocks.

While the evolution of human tools signaled steps in cognitive advancement, it's likely that the slight shifts in capuchin tools are indicative of subtler changes, such as a new environment or available food or tool materials.

"If you define 'Stone Age' as a time period when individuals are using stones as tools, capuchins have their own Stone Age, that's not a problem," Proffitt told National Geographic. "Whether that Stone Age will develop into something far more complex, I have absolutely no idea."