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On Father’s Day in June 2018, Samantha Good was working on an excavation in Drimolen Cave in the Cradle of Humankind in South Africa. She discovered what appeared to be a canine tooth sticking out of the loose brown sediment. Ms. Good continued to dig until she found two more teeth and part of the palate, then alerted her instructors.
“I think I said something interesting is going on,” recalls Ms. Good, an undergraduate anthropology student at Vancouver Island University in British Columbia who attended a field school. on the site. “And it was actually something very interesting.”
Angeline Leece, a paleoanthropologist at La Trobe University in Melbourne, Australia, came to see what Ms. Good had found.
“I think my breathing stopped for a second,” Dr Leece said. “I looked at her and didn’t say anything. But she saw my face and she said, ‘Yeah, that’s what I thought.’
Mrs. Good would eventually learn that she had unearthed a two-million-year-old skull that belonged to Paranthropus robustus, our ancient human cousin with big teeth and a small brain. It is the oldest and best preserved specimen found to date of the species, which lived nearby and may have competed for resources with our direct ancestor Homo erectus. And the skull provides the best-known evidence of an ancestor of humanity evolving to adapt to a changing climate, which a team of researchers detailed Monday in the journal Nature Ecology & Evolution.
Around two million years ago, this region of South Africa would have experienced chaotic climate change. The regional environment has changed from wetter and more lush conditions to drier and more arid conditions. In order for a species like P. robustus to survive in such terrain, it probably would have had to be able to chew tough plants. But the specimen found in Drimolen cave did not appear to match what some scientists had previously said about the human cousin.
They labeled the skull DNH 155 and determined that it belonged to a man. While other skulls had been found at Drimolen, they were mostly female, and this male was smaller than the P. robustus males found in a nearby cave called Swartkrans, which was 200,000 years younger than Drimolen.
Some scientists have suggested that since they found mostly large males at Swartkrans and mostly small females at Drimolen, the size differences could be attributed to sexual dimorphism or physical differences between males and females seen in species, such as manes in lions. The argument was that, more or less, only men lived in Swartkrans and only women in Drimolen.
“Now that didn’t feel right to me,” Dr Leece said. “What looked like me instead was that we have men and women in Drimolen, and men and women in Swartkrans, but those in Drimolen were overall smaller.”
That day, in the cave, she slipped her finger under the earth and felt a large sagittal crest on the top of her head. There were so many bones that the excavators used a special preservative glue to bond the fossils and sediment together to make sure they didn’t lose anything.
Dr Leece and Andy Herries, a geoarchaeologist also at La Trobe, took the specimen out of the ground in a large block of earth and bone and handed it to Jesse Martin, a doctoral student at the university, for qu ‘he reconstructs it minutely.
After a few weeks of sticking the bones and sucking up dirt with a straw, Mr Martin revealed the spotted skull that was trapped in the sediment. The DNH 155 was so well preserved that one of his team, David Strait, a paleoanthropologist at the University of Washington in St. Louis, pointed out that he had intact nasolacrimal ducts, where the tears were flow. He said to Mr. Martin: “This Paranthropus could have cried.
As well as being smaller than the male P. robustus who lived in Swartkrans, the DNH 155’s skull indicated that his chewing muscles were not as strong as theirs. Mr Martin said the differences suggest that DNH 155 and the other P. robustus found at Drimolen were smaller not because they were all females, but rather because they were earlier forms of the species. belonging to a different population that had not yet been subjected to the environmental pressures that would promote taller sizes and stronger jaw muscles.
“It didn’t turn into that huge chewing and grinding machine that it will later become,” said Martin.
The change would have been the result of a microevolution or evolutionary change occurring within a species. Such a morphological change, the scientists said, was likely the result of the adaptation of P. robustus to this changing climate, members of the species who were able to obtain sufficient nutrition through a change in their surviving food supply and transmitting their traits to their offspring.
Amélie Beaudet, a paleoanthropologist at the University of Cambridge in England who was not involved in the study, said the findings of this study will encourage scientists to reconsider some previous hypotheses about how and why the P. robustus specimens belonging to to the same species may resemble. so different.
It’s also important that the study’s authors did not announce that the find was a new species of fossil hominids, said Marcia Ponce de León, a paleoanthropologist at the University of Zurich in Switzerland. Instead, they asked “the interesting question of how a known species has changed in the course of its evolution.”
Because Mrs. Good found DNH 155, she was granted consecration rights. Fittingly, since it was the ‘Father’s Day fossil’, she dedicated it to her father, Ian.
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