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On Father’s Day in June 2018, Samantha Good was working on an excavation in the Drimolen Cave in the Cradle of Humanity in South Africa. He discovered what appeared to be a canine tooth protruding from the melted brown sediment. Good kept digging until he found two more teeth and a partial palate, then alerted his instructors.
“I think I said ‘Something interesting is going on,'” recalled Good, a college student studying anthropology at Vancouver Island University in British Columbia who was attending a field school at the site. “And it was actually something very interesting.”
Angeline Leece, a paleoanthropologist at La Trobe University in Melbourne, Australia, came to see what Good had discovered.
“I think my breathing stopped for a second,” Leece said. “I looked up at her and didn’t say anything. But she saw my face and said, ‘Yes, that’s what I thought.’ “
Eventually Good would discover that he had unearthed a 2-million-year-old skull that belonged to Paranthropus robustus, our ancient, broad-toothed, small-brained human cousin. It is the first and best preserved specimen of the species found so far, which lived alongside and may have competed for resources with our direct ancestor Homo erectus. And the skull provides the best-known evidence of a human ancestor evolving to adapt to a changing climate, which a team of researchers detailed Monday in the journal. Nature, ecology and evolution.
This area of South Africa is believed to have undergone chaotic climate change about 2 million years ago. The regional environment has transformed from more humid and luxuriant conditions to drier and more arid conditions. In order for a species like P. robustus to survive on such soils, it probably would have had to be able to chew on resistant plants. But the specimen found in the Drimolen cave did not seem to fit with what some scientists had previously claimed about the human cousin.
They labeled the skull with DNH 155 and determined it belonged to a male. While other skulls had been found in Drimolen, they were mainly 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 suggested that because they had found mostly large males in Swartkrans and mostly small females in Drimolen, the size differences could be attributed to sexual dimorphism or physical differences between males and females observed in the species, such as the manes in the lions. The argument was that, more or less, only males lived in Swartkrans and only females in Drimolen.
“Now, it didn’t feel right,” Leece said. “What it seemed to me was that we have boys and girls in Drimolen, and boys and girls in Swartkrans, but the Drimolen were just smaller overall.”
That day in the cave, he slipped his finger under the earth and felt a large sagittal crest on the top of his skull. There were so many bones that excavators used special conservative glue to adhere the fossils and sediments to make sure they didn’t lose anything.
Leece and Andy Herries, a geoarchaeologist also in La Trobe, took the specimen off the ground in a large block of earth and bone and delivered it to Jesse Martin, a doctoral student at the university, to meticulously rebuild together.
After a few weeks of gluing the bones and vacuuming the earth with a straw, Martin revealed the speckled skull that was trapped in the sediment. DNH 155 was so well preserved that one of his team members, David Strait, a paleoanthropologist at Washington University in St. Louis, observed that he had intact nasolacrimal ducts, which is where the tears flow. He said to Martin: “This Paranthropus could have cried.”
In addition to being smaller than the male of P. robustus living in Swartkrans, the skull of the DNH 155 indicated that its chewing muscles were not as strong as theirs. Martin said the differences suggest that DNH 155 and the other P. robustus found at Drimolen were smaller not because they were all female, but rather because they were earlier forms of the species belonging to a different population that had not yet undergone ‘environment. pressures that would favor larger sizes and stronger jaw muscles.
“It basically hasn’t become this massive chewing and grinding machine it will become later,” said Martin.
The change would have been the result of microevolution or an evolutionary change that occurs within a species. Such a morphological change, the scientists said, was likely the result of P. robustus’s adaptation to that changing climate, with members of the species being able to obtain enough nutrition from a change in their food supply by surviving and transmitting the treat them to 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 earlier hypotheses about how and why P. robustus specimens belonging to the same species. so different.
It’s also important that the study authors didn’t announce that the find was a new fossil species of 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 changed during its evolution”.
Since Good found DNH 155, she was granted dedication rights. Fittingly, since it was the “Father’s Day Fossil,” he dedicated it to his father, Ian.
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