Dental News - New research on mandible and premolar fossils could rewrite human history

Dental Tribune International

Fri. 16. June 2017

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TÜBINGEN, Germany: For the general public, the debate as to where humankind originated might not seem like a current topic. However, the highly contentious subject within the science world continues to be debated, most notably in two recently published studies investigating the dentognathic morphology of the Graecopithecus freybergi mandible and premolar fossils. The findings indicate that the split of the human lineage occurred in the eastern Mediterranean and not in Africa.

Researchers from Australia, Bulgaria, Canada, France, Germany and Greece collaborated on the two papers, outlining a possible new scenario for the beginning of human history. They were headed by Prof. Madelaine Böhme, from the Senckenberg Centre for Human Evolution and Palaeoenvironment at the University of Tübingen, and Prof. Nikolai Spassov, from the Bulgarian Academy of Sciences.

In the first study, scientists utilised new CT techniques and 3-D reconstructions to recreate the internal structures of the mandible and premolar fossils. From this, they discovered that the premolar roots were fused together.

Mandible has additional dental features

“While great apes typically have two or three separate and diverging roots, the roots of Graecopithecus converge and are partially fused—a feature that is characteristic of modern humans, early humans and several pre-humans (Ardipithecus and Australopithecus),” said Böhme.

Furthermore, the mandible has additional dental root features, which suggest that the G. freybergi species might belong to the prehuman lineage. “We were surprised by our results, as pre-humans were previously known only from sub-Saharan Africa,” said Jochen Fuss, a Tübingen doctoral student involved in this part of the study.

In addition, it is suggested that G. freybergi is several hundred thousand years older than the oldest potential prehuman from Africa, the 6- to 7-million-year-old Sahelanthropus tchadensis from Chad. Dating the sedimentary sequence of the G. freybergi fossils with physical methods, scientists established a nearly synchronised age for both the mandible and the premolar—7.240 and 7.175 million bp. "This dating allows us to move the human–chimpanzee split into the Mediterranean area,” said co-author Prof. David Begun, from the University of Toronto.

Phytoliths particles indicate existence of savannah biome

In the second study, scientists reconstructed hominid environments, which are critical to the understanding of human evolution. As with the out of East Africa theory, the evolution of prehumans may have been driven by dramatic environmental changes. The team demonstrated that the North African Sahara Desert may have originated more than seven million years ago, based on geological analyses of the sediments in which the two fossils were found. An analysis of uranium, thorium and lead isotopes in individual dust particles yielded an age of between 0.6 and 3 billion years and inferred an origin in North Africa. In addition, the dusty sediment had a high content of different salts. Scientists from Tübingen explained the significance of this: “These data document for the first time a spreading Sahara 7.2 million years ago, whose desert storms transported red, salty dusts to the north coast of the Mediterranean Sea in its then form.”

Using a combination of new methodologies, the researchers additionally studied microscopic fragments of charcoal and fossilised particles of plant tissue, called phytoliths, and found evidence to suggest that a savannah biome in Europe must have been formed prior to the Sahara in North Africa. Many of the phytoliths identified derived from grasses, particularly from those that use the C₄ metabolic pathway of photosynthesis, which is common in today’s tropical grasslands and savannahs. The global spread of C₄ grasses began eight million years ago on the Indian subcontinent. Their presence in Europe was previously unknown.

“The phytolith record provides evidence of severe droughts, and the charcoal analysis indicates recurring vegetation fires,” said Böhme. She added that “the incipient formation of a desert in North Africa more than seven million years ago and the spread of savannahs in Southern Europe may have played a central role in the splitting of the human and chimpanzee lineages.” She calls this hypothesis the “North Side Story”.

The studies, titled “Potential hominin affinities of Graecopithecus from the late Miocene of Europe” and “Messinian age and savannah environment of the possible hominin Graecopithecus from Europe”, were published on 22 May in the PLOS ONE journal.