‘Whodunit’ mystery arises over trove of prehistoric Kenyan stone tools

Scientists have a mystery on their hands after the discovery of 330 stone tools about 2.9 million years old at a site in Kenya, along Lake Victoria’s shores, that were used to butcher animals, including hippos, and pound plant material for food.

Which of our prehistoric relatives that were walking the African landscape at the time made them? The chief suspect, researchers said on Thursday in describing the findings, may be a surprise.

The Nyayanga site artifacts represent the oldest-known examples of a type of stone technology, called the Oldowan toolkit, that was revolutionary, enabling our forerunners to process diverse foods and expand their menu. Three tool types were found: hammerstones and stone cores to pound plants, bone and meat, and sharp-edged flakes to cut meat.

To put the age of these tools into perspective, our species Homo sapiens did not appear until roughly 300,000 years ago.

Scientists had long believed Oldowan tools were the purview of species belonging to the genus Homo, a grouping that includes our species and our closest relatives. But no Homo fossils were found at Nyayanga. Instead, two teeth – stout molars – of a genus called Paranthropus were discovered there, an indication this prehistoric cousin of ours may have been the maker.

“The association of these Nyayanga tools with Paranthropus may reopen the case as to who made the oldest Oldowan tools. Perhaps not only Homo, but other kinds of hominins were processing food with Oldowan technology,” said anthropologist Thomas Plummer of Queens College in New York City, lead author of the research published in the journal Science.

The term hominin refers to various species considered human or closely related.

“When our team determined the age of the Nyayanga evidence, the perpetrator of the tools became a ‘whodunit’ in my mind,” said paleoanthropologist and study co-author Rick Potts, director of the Smithsonian National Museum of Natural History’s Human Origins Program. “There are several possibilities. And except for finding fossilized hand bones wrapped around a stone tool, the originator of the early Oldowan tools may be an unknown for a long time.”

The molars represent the oldest-known fossils of Paranthropus, an upright-walker that combined ape-like and human-like traits, possessing adaptations for heavy chewing, including a skull topped with a bony ridge to which strong jaw muscles were attached, like in gorillas.

Other hominins existing at the time included the genus Australopithecus, known for the famous even-older fossil “Lucy.”

“While some species of nonhuman primates produce technologies that assist in foraging, humans are uniquely dependent on technology for survival,” Plummer said.

All later developments in prehistoric technologies were based on Oldowan tools, making their advent a milestone in human evolution, Potts said. Rudimentary stone tools 3.3 million years old from another Kenyan site may have been an Oldowan forerunner or a technological dead-end.

The Nyayanga site today is a gully on Homa Mountain’s western flank along Lake Victoria in southwestern Kenya. When the tools were made, it was woodland and grassland along a stream, teeming with animals.

Until now, the oldest-known Oldowan examples dated to around 2.6 million years ago, in Ethiopia. The species Homo erectus later toted Oldowan technology as far as Georgia and China.

Cut marks on hippopotamus rib and shin bones at Nyayanga were the oldest-known examples of butchering a very large animal – called megafauna. The researchers think the hippos were scavenged, not hunted. The tools also were used for cracking open antelope bones to obtain marrow and pounding hard and soft plant material.

Fire was not harnessed until much later, meaning food was eaten raw. The researchers suspect the tools were used to pound meat to make it like “hippo tartare.”

“Megafauna provide a super abundance of food,” Plummer said. “A hippopotamus is a big leather sack full of good things to eat.”