In the summer of 1944, workers digging a bunker in Nazi-occupied Athens came across a fossilized lower jaw with badly damaged teeth. The jaw was shown to a geologist named Bruno von Freyberg who brought it back to Germany and misidentified it as that of a monkey. Years later, the fossil was re-examined and recognized as belonging to an ancient species of ape, dubbed Graecopithecus freybergi. But with few preserved features that would reveal anything further about the creature, the jaw was all but forgotten by scientists.
Now, that same jaw, together with a lone tooth found in Bulgaria, have re-emerged as the centrepiece of new scientific study that makes a provocative claim: The sparse remains are not from just any species of ape, the team behind the study argues. Rather, they appear to be the oldest known traces of hominins, the group that branched off from the ancestors of chimpanzees millions of years ago and evolved into modern humans.
If the interpretation is correct, it could mean that the hominin line first showed up in southeastern Europe, rather than in Africa, as is generally thought by experts.
"It opens up that possibility," said David Begun, a professor of anthropology at the University of Toronto and a co-author on the study, published Monday in the journal PLOS ONE. "People need to stop just thinking about Africa as the only possible location for this divergence. It could well have happened in Europe."
The reason this matters has nothing to do with geographical bragging rights, Dr. Begun said. It's to help researchers arrive at a clearer picture of how and why hominins developed a unique set of adaptations, including smaller canine teeth and the ability to walk upright, that would later prove to be key evolutionary steps on the road to humanity.
"You need to know the ecological setting so that you can speculate on the reasons for it," Dr. Begun said.
To be clear, there is no question that our species, Homo sapiens, originated in Africa between 100,000 and 200,000 years ago and subsequently spread around the globe. Fossils of hominins found in Africa make a compelling case that for millions of years the continent has been the focal point for the development of human-like traits, including tool use and large brain size.
But prior to about 4.4 million years ago, the fossil record becomes sparse. A creature called Sahelanthropus, represented by a cranium and a few other fragments found in Chad that date to about seven million years ago, is currently on of the best candidates for the earliest hominin.
In 2011, Madelaine Bohme, a paleontologist at the University of Tuebingen, was involved in the discovery of an ape's tooth in Bulgaria that has been dated at about 7.2 million years. This is slightly older than Sahelanthropus, but much more recent than other apes that were known from the fossil record to inhabit the Balkans.
Dr. Bohme wondered what kind of ape the tooth represented. She recalled learning about the ape jaw that had turned up in Greece and wondered if there was a connection.
"My feeling was it could be of similar age to the Bulgarian tooth," she said.
Dr. Bohme then embarked on a one-and-a-half year quest to re-locate the Freyberg jaw, which finally turned up in a specimen box at the University of Erlangen-Nurmeberg.
With the jaw in hand, Dr. Bohme and her team made a detailed investigation using a micro CT scanner, which employs focused X-rays, to produce three dimensional images of the interior of a fossil. The researchers were able to identify the roots of the teeth still embedded in the jaw.
Unlike the eroded outer surfaces of the teeth, the roots were well preserved and displayed features that the researchers say are only known to be present in hominin fossils. They also showed that it came from sediment that closely matched the 7.2 million year old age for the Bulgarian tooth and that was rich in reddish dust blown in from the Sahara.
Putting it all together, Dr. Bohme said the fossils paint a picture of an early hominin lineage that became cut off from African great apes during a drying out period that started around 7.4 million years ago and that turned the Sahara desert into an impassible barrier.
"To make two separate lineages, you need a permanent stop of genetic flow," she said.
Later, when the regional climate became more humid, hominins would have been able to enter Africa from the north but by then would have been genetically isolated from the ancestors of chimps already living in African forests.
The researchers are careful not to overstate their case. For example, there is no way to know if Graecopithecus walked upright, which would clearly identify it as a hominin. Further excavations are planned in both Greece and Bulgaria to see if additional material can be unearthed.
Dr. Begun, who is known for proposing a European origin for non-human African apes at an early time in geological history, said he expects the new study to generate debate.
Kieran McNulty, an anthropologist at the University of Minnesota who was not involved in the study, said the work on the Greek fossil was impressive but the jaw could not be definitively shown to be a hominin because so little is known about the deep past of ape species that were not part of the human line.
"It's really difficult to interpret what those earliest common ancestors would have looked like, because all we can see is the end product of millions of years of evolutions in chimps and gorillas," he said.
He added that the weight of evidence still favours a hominin origin in Africa, including the long line of hominin fossils and the presence of chimps and gorillas there today.
Herman Pontzer, an evolutionary anthropologist at Hunter College in New York, agreed the work was thorough and important, but the results so far are not enough to overthrow the conventional picture of hominin origins, he said.
"While it's exciting to think about the possibilities," he added, "I don't think this is going to change the way I teach human evolution."