Some monkeys accidentally make stone-like tools

Monkeys in southern Thailand use rocks to rub open oil palm nuts, accidentally crushing the stone shards that pop out of their nutcrackers. Researchers say that these meat-like sharp stone tools were created by some presumed industry by ancient hominids.

Thailand’s long-tailed macaques (Macaca fascicularis) to produce shards that could easily be mistaken for stone flints previously found at 17 East African hominid sites from about 3.3 million to 1.56 million years ago, say archaeologist Thomas Proffitt and colleagues. The discovery suggests that ancient people may have sometimes accidentally created rock while using rocks for nuts, bones or other objects, scientists report on March 10. Journal of Sciences.

Previous research has already shown capuchin monkeys in Brazil to be unknowingly producing a hominid-like carnivore (SN: 10/19/16).

Observations of rock bashing by these two species of apes undermine the long-held assumption that hominids deliberately made some of the oldest stone quarries, including some examples of the earliest known tools, Proffitt says.SN: 6/3/19). It is time to rethink how such determinations are made.

Proffitt’s group identified 219 whole and broken into 40 macaque nuts burned in places on the island where the monkeys live. The team also found rocks showing damage consistent with being used either as hammering tools or hammering beaks.

Some differences exist between macaque and hominid lacrimal stones, says Proffitt, of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. For example, many macaques show loss of meat on only one side, versus multiple losses in hominid artifacts.

Such clues can help archaeologists develop rules for evaluating whether ancient hominid rocks were made intentionally or accidentally, Proffitt suspects.