André Ueberbach / CC A-S A 2.0 GER
Long-tailed macaques (Macaca fascicularis aurea) on Piak Nam Yai, one of Thailand's islands, are using stone tools to process and eat shellfish and nuts, a new study led by Dr. Michael Haslam from the University of Oxford shows. The study actually provides the first archaeological evidence of tool use by Old World monkeys, and finds that the macaques have been using the technique for decades, if not thousands of years.
"We find that primates with much smaller brains than humans have innovative ways of
exploiting the food sources available to them," Dr. Haslam said.
"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."
The macaques break open oysters attached to large boulders. They dislodge the top half of the shell using their crushing tool and then scoop out the meat with their fingers. Once a macaque has a good stone for the job, they keep it to crack open other shells or nuts.
The macaques often discard their tools around where they had enjoyed their meal. So, when the animals had left the shore, Dr. Haslam's team went on land to closely examine the tools for marks. They found features such as pitting on the flat side, or crushing and fracture marks on the narrow ends of the stones.
The scientists also excavated the area beneath a prominent boulder for evidence of discarded stone tools used by previous generations of macaques. Having identified the tell-tale marks of food processing, the team spotted ten tools in the oldest archaeological layer, at 65 cm below the surface.
The excavated tools have been dated between 10 and 50 years old by obtaining radiocarbon dates for oyster shell debris found in the same undisturbed archaeological layer.
"What we don’t have at the moment is a body of archaeological evidence to compare
the evolutionary behavior of other primates with our own," Dr. Haslam said.
"Uncovering the history of the macaques’ foraging behavior is a first step."
"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."