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Paleoanthropologists have discovered a two-million-year-old adult hominid skull – the first known and best-preserved specimen of Paranthropus robustus ever found.
Researchers from the Department of Archeology at La Trobe University in Melbourne, Australia, led the excavation, reconstruction and analysis of the rare male fossil from the main Drimolen quarry north of Johannesburg, South Africa.
Discovered in 2018 on South African Father’s Day (June 20), the DNH 155 fossil is also known as a Father’s Day fossil.
Paranthropus robustus was a large-toothed, small-brained hominin that coexisted with our first direct human ancestors as a “cousin species”. The researchers say the DNH 155 sample they found provides the first high-resolution evidence for microevolution within one of the earliest hominid species.
Co-lead author and La Trobe PhD candidate Jesse Martin said the findings, published today in Nature Ecology & Evolution, could lead to a revised system for classifying and understanding the paleobiology of human ancestors.
“Showing that Paranthropus robustus is not particularly sexually dimorphic removes much of the urge to assume that they lived in gorilla-like social structures, with large dominant males living in a group of smaller females,” said Martin.
‘Drimolen’s male fossil DNH 155 is very similar to female specimens from the same site, while Paranthropus robustus from other sites are remarkably different.’
Martin said the discovery is a rare example of microevolution within a human lineage, showing that Paranthropus robustus evolved their iconic chewing adaptations incrementally, perhaps over hundreds of thousands of years, in response to the changes. environmental.
“The Drimolen fossils represent the first known step in the long evolutionary history of Paranthropus robustus,” said Martin.
The director of the Australian Research Council funded Drimolen project, Professor Andy Herries of La Trobe, said: “The DNH 155 skull shows the beginning of a very successful lineage that existed in South Africa for a million years. Like all other creatures on earth, our ancestors adapted and evolved based on the landscape and environment around them to maintain success. For the first time in South Africa, we have the resolution of dating and morphological evidence that allows us to see such changes in an ancient hominid lineage over a short span of time. “
“We believe these changes took place during a time when South Africa was drying up, leading to the extinction of a number of contemporary mammal species. Climate change is likely to have produced environmental stressors that drove evolution within Paranthropus robustus. “
The paper’s lead co-author, Dr. Angeline Leece of La Trobe, said it was important to know that Paranthropus robustus appeared around the same time as our direct ancestor Homo erectus, the fossil baby the team discovered in the same site as Drimolen in 2015.
‘These two very different species, Homo erectus with their relatively large brains and small teeth, and Paranthropus robustus with their relatively large teeth and small brains, represent divergent evolutionary experiments,’ said Dr. Leece.
“Over time, Paranthropus robustus likely evolved to generate and resist higher forces produced when biting and chewing food that was difficult or mechanically challenging to process with jaws and teeth, such as tubers. Future research will clarify whether environmental changes have placed populations under food stress and how this has affected human evolution. “
“While we were the lineage that ultimately won, fossil records two million years ago suggest that Paranthropus robustus was much more common than Homo erectus in the landscape.”
Stephanie Baker, co-director of the Drimolen project, said: “This extraordinary study of ancient populations highlights the Drimolen team’s fine-scale approach to understanding incremental changes in now extinct ancestors. We can now begin to understand what associated morphological and behavioral adaptations first came in Paranthropus robustus as the landscape became more and more arid. This is a fundamental step in understanding how different species of human beings have competed for resources at this critical moment in our evolution. “
Professor David Strait of Washington University in St. Louis, co-director of the field school bringing students from South Africa and around the world to work at Drimolen, said the discovery has broad implications for the interpretation of diversity in human fossil record.
“We believe paleoanthropology needs to be a little more critical in interpreting the variation in anatomy as evidence of the presence of multiple species. Depending on the age of the fossil specimens, the differences in bone anatomy could represent changes within lineages rather than evidence of multiple species. “
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