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CAS professor helps make historic discovery

TAMPA, Fla. – Bones unearthed by a team of scientists in Ethiopia show that early human ancestors used tools a million years earlier than previously documented, which means many textbooks will have to be rewritten as the world gains a new perspective on human development. The August 12 issue of the journal < ahref=””> Nature recounts the story of the landmark discovery by the people who made it.

USF Geology Assistant Professor Jonathan Wynn is part of the Dikika Research Project (DRP) team, led by paleoanthropologist Zeresenay Alemseged. The team works in the Afar Region of Ethiopia and was searching through sedimentary deposits when the discovery was made. During a day intended for the intense collection of fossil bones, an effort that resembles searching for a needle in a haystack, another team member, archeologist Shannon McPherron noticed a couple of otherwise unremarkable large animal bones. The rib and femur fragments had unique markings on them that caught the team’s attention. They were cautiously thrilled, but put initial excitement on hold until experts could take a closer look.

After the team gained permission to export these exceptional fossils so that they could be put under a microscope and diagnosed, the bones were flown to Arizona State University, where zooarcheologist Curtis Marean and materials research scientist Hamdallah Bearat performed the mark identifications.

“We waited with anticipation and bated breath until the results came,” Wynn said. “Yes, everything about them was consistent with human tool use. Just as had been thought, someone had clearly made carving actions and used force to break the bone to get at the marrow with a tool of some kind. And this was done before the bones were buried, in the distant geological past.”

The team realized that it was a matter of “when” that would make the find so significant. The bones date to roughly 3.4 million years ago. Wynn’s research was instrumental in coming up with this estimate. He used the location of volcanic ash deposits known as tuffs to determine the age of the bones. They were found between tuffs already documented by Wynn as having fallen to earth 3.42 and 3.24 million years ago.

“Chemical and isotopic composition of volcanic rocks provide something of a date stamp which scientists use to date the material sandwiched between the layers,” Wynn said. “The bones were measurably closer to the lower tuff and below other areas that were documented so I was able to refine that number to 3.4 million.”

Prior to this, the oldest known stone tools have been similarly dated to between 2.6 and 2.5 million years ago at a nearby site in Ethiopia called Gona. Also found nearby in Ethiopia, at Hadar, an early Homo species jaw from that time period had led most paleoanthropologists to believe that this group was the first and only group of human ancestors to use tools.

Wynn has been working with the international team of researchers since 2002 when his reputation as one of a handful of experts in the geology of early humans in the African Rift led to an invitation from Alemseged to be part of DRP. The Afar area is rich in fossils and held a lot of promise.

Alemseged, from the California Academy of Science, and his team had already made headlines with his find of Selam in 2000, a young Australopithecus afarensis girl who lived about 3.3 million years ago known as Lucy’s baby. Lucy was the nickname for a skeleton found in Hadar, Ethiopia, in 1974. It has taken five years, and counting, to free Selam’s bones from the surrounding rock and sediment, and another year to date them. This latest find, only a few hundred meters away from Selam, provides the first evidence that Lucy’s species, Australopithecus afarensis, used stone tools and consumed meat.

Paleoanthropologist Aleseged said, “This discovery dramatically shifts the known timeframe of a game-changing behavior for our ancestors. …Tool use fundamentally altered the way our earliest ancestors interacted with nature, allowing them to eat new types of food and exploit new territories. It also led to tool making – the precursor to such advanced technologies as airplanes, MRI machines, and iPhones.

“Our closest living relatives, the chimps and bonobos, don’t hunt or scavenge animals this size, so this suggests that the Dikika Australopithecines had already begun to engage in hunting or scavenging larger mammals.”

This notion conjures up vivid imagery.

McPherron, the lead author of the study, and a scientist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, said, “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.”

The area yields so many fossils because it is in a river valley that runs through the Ethiopian Rift, which is steadily dropping, surrounded by the shoulders of the Rift Valley that are steadily moving up along active tectonic faults. So, sediment from the highlands regularly washes down into the valley carrying and burying all manner of material. Nearby volcanoes also contribute ash layers at intervals. This process has preserved a very long record of human evolution and Wynn said that the fossils from this area are exceptionally well-preserved because they are buried so rapidly.

“You often find things intact, even nearly complete animal skeletons in anatomical position, and when animals have been butchered, even things like cut marks are preserved through the burial process,” he said.

Human fossils from the layer that yielded the tools may provide evidence about whether or not they ate meat as the tools appear to indicate. Wynn hopes that a study of the chemical composition of the hominids can disclose more information about human diets from that period.

“We would be able to obtain more evidence in the chemical composition of the teeth, based on the principle that ‘you are what you eat,’ in other words, the chemical and isotopic ‘signatures’ from your diet are reflected in the composition of your teeth and bones,” Wynn said. “A look at their composition may be able to give us more information about the types of food they ate.”

Wynn’s research also is helping to develop an environmental snapshot of the time the tool-wielding hominids lived.

“They lived close to a large shallow lake surrounded by woodlands, where a river delta deposited large amounts of sediment from flooding events that occurred on a large river system,” he said. “The general environment was significantly wetter than the region is today, with lush vegetation such as reeds and tall grasses watered by seasonal floods.”

Today in this region there is a great deal of erosion. The only current landscape that resembles the past is along the nearby Awash River that cuts through the area Here, hippos, oryxes, gazelles, zebra, hyenas, jackals and ostriches can be found, some of which have wandered through Wynn’s base camp on occasion. He and a complement of fellow scientists along with 30 local tribesmen hired to serve as guides, prospectors and camp staff, have been visiting the area for several years. They avoid the hot summers and the rainy season in the fall and spring, leaving November through February for digging.

Wynn grew up surrounded by “lots of interesting rocks” in Arizona, Utah and California but it wasn’t until he went to college as a business major that he switched directions. A geology class reminded him of his curiosity about and appreciation of those rocks. After earning a bachelor’s and a master’s degree at the University of Utah, he headed to the University of Oregon for his PhD – all in geology. He has been at USF since 2006.

“When I was doing graduate work, I was working in the Turkana Depression, an arid lowland lake basin in Northern Kenya, on the border of Ethiopia. In the distance, through the haze of the dry, dusty desert, I could vaguely see the pile of volcanic rocks shrouded in mist over in Ethiopia and thought, ‘I’d like to work there someday,’” Wynn said. And that’s in fact where he has spent the past eight years working with Alemseged and the Dikika Research Group.

Meanwhile, a number of other important projects vie for his attention. Wynn is studying soil carbon in Florida, gathering data on the rates at which CO2 is pulled out of the atmosphere in different types of soils.

“Soils play a major role in the global carbon cycle and help to store some of the carbon dioxide (CO2) that would otherwise accumulate in the atmosphere,” Wynn said. “In fact, soils and land plants contain as much as three times the carbon that is currently found in the atmosphere. And, we know comparatively little about how soil carbon responds to human activity, compared to the oceans. In understanding how the water content in soil slows the decomposition of soil carbon – we can see how wetlands with water tables connected to the Florida’s aquifers, together with the actions of soil microorganisms may help to mitigate atmospheric CO2 levels.

“These findings could help us to make better decisions about utilizing Florida’s precious water resources, and what impact these decisions may have on atmospheric CO2.”

Wynn changes gears further by working with colleagues in Romania to study how sulfur-bearing minerals in caves formed, and how ice deposits in caves preserve a record of past global climate change. All of this keeps him both fascinated, and busy thinking of new ideas.

These projects and teaching will get more of his attention. The Dikika team is taking a needed break from digging in Ethiopia, for time to study their findings further and write about them. They plan to return in two years.

When they do, they hope to find out whether the hominids used naturally occurring rocks or actually fashioned their own tools from rocks.

”Now that we know that hominids other than the large-brained Homo used stone tools at this early stage in human history, we want to look for places where these hominids may have found stones that were large enough to break into sharp tools,” Wynn said. “To do this, we plan to search through nearby banks of river cobbles that were deposited on ancient gravel bars. With the current evidence of tool use in hand, we can hypothesize that these early hominids picked up stones from these river banks, and went out into the open savannas to obtain food.

“It is likely that this type of activity would have meant new horizons and new opportunities for our ancestors 3.4 million years ago.”

Filed under:Arts and Sciences School of Natural Sciences and Mathematics Geology Research  
Author: Barbara Melendez