August 12, 2010

Human Ancestors Used Stone Tools Million Years Earlier

Fossilized bones from two ancient animals in Ethiopia show signs of human butchering, pushing back the earliest known evidence for the use of stone tools by nearly a million years, according to researchers. 

The bones appear to have been butchered about 3.4 million years ago, and are the first evidence of the use of stone tools for meat consumption by Australopithecus afarensis, the species best known for the fossil called "Lucy," Zeresenay Alemseged, Curator of Anthropology at the California Academy of Sciences, told the Associated Press (AP).

Alemseged led an international team of scientists who discovered the fossilized bones while working in the Afar Region of Ethiopia.

The researchers said the fossilized bones showed unambiguous signs of stone tool use"”cut marks inflicted while carving meat off the bone and percussion marks created while breaking the bones open to extract marrow.

"This discovery dramatically shifts the known timeframe of a game-changing behavior for our ancestors," Alemseged wrote in an August 11th press release.

"Tool use fundamentally altered the way our early ancestors interacted with nature, allowing them to eat new types of food and exploit new territories. It also led to tool making"”a critical step in our evolutionary path that eventually enabled such advanced technologies as airplanes, MRI machines, and iPhones."

"This find will definitely force us to revise our text books on human evolution, since it pushes the evidence for tool use and meat eating in our family back by nearly a million years," he said.

"These developments had a huge impact on the story of humanity."

Until now, the oldest known evidence of butchering with stone tools came from Bouri, Ethiopia, where several cut-marked bones were dated to about 2.5 million years ago.  The oldest known stone tools, also dated to around that time, were found at nearby Gona, Ethiopia.

The current find from Alemseged and his "Dikika Research Project" team were found just 600 feet away from the site where Alemseged's team discovered "Selam" in 2000. Dubbed "Lucy's Daughter", Selam was a young A. afarensis girl who lived about 3.3 million years ago and represents the most complete skeleton of a human ancestor discovered to date.

"After a decade of studying Selam's remains and searching for additional clues about her life, we can now add a significant new detail to her story," Alemseged said.

"In light of these new finds, it is very likely that Selam carried stone flakes and helped members of her family as they butchered animal remains."

The location and age of the butchered bones from Dikika clearly indicate that a member of the A. afarensis species inflicted the cut marks, since no other hominin lived in this part of Africa at the time. These fossils provide the first direct evidence that this species, which includes such famous individuals as Lucy and Selam, used stone tools.

"Now, when we imagine Lucy walking around the east African landscape looking for food, we can for the first time imagine her with a stone tool in hand and looking for meat," said Dr. Shannon McPherron, an archeologist with the Dikika Research Project and research scientist at the Max Planck Institute for Evolutionary Anthropology in Leipzig.

"With stone tools in hand to quickly pull off flesh and break open bones, animal carcasses would have become a more attractive source of food. This type of behavior sent us down a path that later would lead to two of the defining features of our species"”carnivory and tool manufacture and use."

To date the butchered bones, project geologist Dr. Jonathan Wynn used a well-documented and dated set of volcanic deposits in the Dikika area. These same deposits had been used to determine Selam's age, and are well known from nearby Hadar, where Lucy was discovered.  The cut-marked bones at Dikika were sandwiched between volcanic deposits that have been securely dated to 3. 24 and 3.42 million years ago, and were located much closer to the older sediment.

"We can very securely say that the bones were marked by stone tools between 3.42 and 3.24 million years ago, and that within this range, the date is most likely 3.4 million years ago," said Wynn, a University of South Florida geologist.

Both of the fossilized bones found at Dikika came from mammals -- one a rib fragment from a cow-sized mammal and the other a femur shaft fragment from a goat-sized mammal.  Both are disfigured by cut, scrape, and percussion marks.

Microscope and elemental analysis revealed that these marks were created before the bones fossilized, meaning that recent damage can be eliminated as the cause of the marks.   Additionally, the marks were consistent with the morphology of stone-inflicted cuts rather than tooth-inflicted marks.

"Most of the marks have features that indicate without doubt that they were inflicted by stone tools," said Dr. Curtis Marean from the Institute of Human Origins at Arizona State University, who helped with the mark identifications.

"The range of actions that created the marks includes cutting and scraping for the removal of flesh, and percussion on the femur for breaking it to access marrow."

Although it is clear that the Australopithecines at Dikika were using sharp-edged stones to carve meat from bones, it is impossible to tell from the marks alone whether they were making their tools or simply finding and using naturally sharp rocks. To date, the researchers have not found any flaked stone tools at Dikika from this time period, which could indicate that the Dikika residents were simply opportunistic about finding and using sharp-edged stones.

But the sedimentary environment at the site suggests another potential explanation.

"For the most part, the only stones we see coming from these ancient sediments at Dikika are pebbles too small for making tools," said McPherron.

"The hominins at this site probably carried their stone tools with them from better raw material sources elsewhere. One of our goals is to go back and see if we can find these locations, and look for evidence that at this early date they were actually making, not just using, stone tools."

Regardless of whether or not Selam and her relatives were making their own tools, the fact that they were using them to access meat and marrow from large mammals would have had wide-ranging implications for A. afarensis, both physically and behaviorally.

"We now have a greater understanding of the selective forces that were responsible for shaping the early phases of human history," said Alemseged.

"Once our ancestors started using stone tools to help them scavenge from large carcasses, they opened themselves up to risky competition with other carnivores, which would likely have required them to engage in an unprecedented level of teamwork."

The research is reported in the August 12 issue of the journal Nature.


Image 1: These two cutmarks were made about 3.4 million years ago, when an Australopithecus afarensis carved meat off the rib bone of a cow-sized mammal. Credit: Dikika Research Project, California Academy of Sciences

Image 2: These two bones from Dikika, which have been dated to roughly 3.4 million years ago, provide the oldest known evidence of stone tool use among human ancestors. Both of the cut-marked bones came from mammals -- one is a rib fragment from a cow-sized mammal, and the other is a femur shaft fragment from a goat-sized mammal. Both bones are marred by cut, scrape, and percussion marks. Credit: Dikika Research Project, California Academy of Sciences

Image 3: Dr. Zeresenay Alemseged, Curator of Anthropology at the California Academy of Sciences, excavates an ancient rhino skull at Dikika, Ethiopia. Alemseged's excavations at Dikika recently unearthed the oldest known evidence of stone tool use among human ancestors. Credit: Dikika Research Project, California Academy of Sciences


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