The discovery of a 2 million-year-old skull in a South African cave is changing our understanding of one of the primitive ancestors of mankind, scientists say in a new study.
The newly discovered fossil specimen of the extinct human species Paranthropus robustus also gives researchers a unique picture of the transformations climate change can bring about in populations living in a changing environment – stimulating adaptations that can make life easier and more likely to survive.
P. robustus, so named for its sturdy appearance with a large, robust skull, jaw and teeth, originated about 2 million years ago in South Africa and eventually became one of the earliest hominin species discovered and studied by the mid-20th th century.
However, not all P. robustus were equally resistant, and we know this thanks to a recently discovered specimen identified as DNH 155.
DNH 155, discovered in 2018 during a field expedition in the Drimolen cave system northwest of Johannesburg, appears to be somewhat different from its genus P. robustus, at least based on the fossil remains found earlier.
DNH 155, male, is significantly smaller than other male P. robustus found in the neighboring area called Svartkrans.
But it's not just geography that separates these two ancient populations. There is also a question of time: about 200,000 years, give or take.
Reconstructed skull DNH 155 (Jesse Martin and David Strait).
'Drimolen predates Svartkran by about 200,000 years, so we believe that P. robustus evolved over time, with Drimolen representing an early population and Svartkrans a later, more anatomically advanced population,' explains author and Ph.D. in paleology Jesse Martin from LaTrobe University in Australia.
The researchers believe that one of the main factors that could have caused this was an episode of climate change that affected the landscape of South Africa about 2 million years ago, when the environment became more open, dry and cooler.
These changes left their mark on many things, including the types of foods that were available for P. robustus, which would require biting and chewing on tough vegetation – foods that DNH 155 would have been difficult to snack on and chew on, given their tooth position and chewing muscles.
“Compared to the geologically younger specimens from nearby Svartkrans, the Dreamolene skull is very clear that it was less adapted to the complex meals on the menu,” says anthropologist Gary Schwartz of Arizona State University.
Despite successful adaptations that slowly altered the body of P. robustus over a period of approximately 200,000 years, the species eventually became extinct. Around the same time, our direct ancestor, Homo erectus, also appeared in the same part of the world.
'These two very different species, H. erectus with their relatively large brains and small teeth, and P. robustus with their relatively large teeth and small brains, are divergent evolutionary branches,' says co-lead author and archaeologist Angelina Lis of Latrobe University.
“While we were the species that eventually evolved into modern humans, the fossil record shows that P. robustus was much more common than H. erectus 2 million years ago.”
The results are published in Nature Ecology & Evolution.
Sources: Photo: (Jesse Martin and David Strait)
