Generations of macaques used stone tools to open oysters, nuts

OXFORD, England, June 10 (UPI) -- New research suggests the wild macaques of coastal Thailand have employed stone tools to pry open oysters and nuts for several generations.

Their use of tools may date back thousands of years, scientists at the University of Oxford say. Researcher recently detailed their discovery in the Journal of Human Evolution. Theirs is the first study to look at archaeological evidence of tool usage among Old World monkeys.

Before scientists began looking for historic remains of tool usage, they watched modern macaques in action. From boats, scientists watched the monkeys scamper across the rocky shore in search of good stones. The macaques used the stones to shatter the top shell of oysters before using their fingers to scoop out and eat the briny flesh.

The monkeys also used stones to get at the meat of snails, nuts and crabs. Scientists noticed that monkeys often held onto stones if they were serving their purpose well, and discarded them near the boulders where they would eat their meals.

"We find that primates with much smaller brains than humans have innovative ways of exploiting the food sources available to them," lead study author Michael Haslam, an archaeologist at the University of Oxford, said in a news release. "Macaques in the forests on the island come down to the shore when the tide is out to forage, and use stones as tools in order to break open shells and hard nut casings to access the food inside."

When mealtime ended, scientists docked their boats and examined the dispensed stone tools for identifying marks. The research team then excavated several feet of sandy soil surrounding the coastal boulders that serve as kitchen tables for the monkeys. They found identical marks, signs of tool usage, on stones found in the oldest archaeological layer. By radiocarbon dating oyster shell fragments, researchers estimated the tools to be between 10 and 50 years old.

Scientists have been looking for ways to compare human and primate evolution, but finding sufficient reference points has proven difficult.

"Uncovering the history of the macaques' foraging behavior is a first step," Haslam said. "As we build up a fuller picture of their evolutionary history, we will start to identify the similarities and differences in human behavior and that of other primates."