Skull Fossils in Cave Show Mix of Human Relatives Roamed South Africa

Skull Fossils in Cave Show Mix of Human Relatives Roamed South Africa

Nestled in South Africa’s Cradle of Humankind, the Drimolen paleocave is an amphitheater hosting the remains of ancient ancestors of humans. Most famous among the hominins found there are Orpheus and Eurydice, a pair of Paranthropus robustus unearthed in 1994 and named after the lovers from Greek mythology. They are just two of more than 160 fossilized specimens of our extinct early relatives dug up at the roofless cave.

Now, archaeologists excavating the site have discovered even more remains that could transform our understanding of when and where our human ancestors and their relatives lived millions of years ago in this part of Africa.

In Science on Thursday, they published a paper identifying the skullcap and teeth of another Paranthropus robustus, as well as the cranium of our direct ancestor, Homo erectus. Both specimens date to between 1.95 and 2.04 million years ago. If confirmed, the findings would be the oldest known Paranthropus robustus, as well as the oldest known Homo erectus, nudging out the next oldest known specimen by 150,000 to 200,000 years.

The discoveries offer evidence that Homo erectus trekked from the bottom of South Africa, across the African continent and into the Caucasus region within only a couple of hundreds of thousands of years.

“That species is beautifully romantic because without Homo erectus there is no Homo sapiens,” said Stephanie Baker, a doctoral student at the University of Johannesburg who oversees the Drimolen site. “He was the first one to take that giant step for mankind.”

Homo erectus roamed the planet for two million years before going extinct, far longer than we Homo sapiens have so far. That makes Homo erectus the most successful species of our family, which also included the Neanderthals and Denisovans, according to Susan Antón, a paleoanthropologist at New York University who wrote a commentary accompanying Dr. Baker and her colleagues’ paper.

The findings also suggest these two early human relatives lived contemporaneously with another of Africa’s hominins, the “ape-man” Australopithecus. First discovered elsewhere in South Africa, the species began disappearing from the fossil record around the time the other two started popping up.

“Here we have evidence of all three genera, Homo, Paranthropus and Australopithecus, sharing the landscape at just about the same time,” said David Strait, a paleoanthropologist at Washington University in St. Louis and a co-author. “It is our first really good look at the time that this replacement is taking place and that’s pretty exciting.”

Paranthropus were shorter than Homo erectus and Australopithecus and they used their massive teeth to grind roots and tubers. Using a technique called paleomagnetism that analyzes how Earth’s magnetic field has changed over time, the team, led by Andy Herries, a geoarchaeologist from La Trobe University in Australia, showed that both the Homo erectus and Paranthrope specimens at the cave site were between 1.95 and 2.04 million years old.

In 2015, Richard Curtis, now a graduate student at La Trobe University, was taking part in a field school program at the site when he found a tiny, thin bit of bone. At the time, the researchers thought it came from a baboon. They continued to uncover similar bones, most no bigger than a stamp.

“These beautiful bits and pieces of crania started coming up,” Ms. Baker said. She wasn’t quite convinced the bones belonged to a baboon, so one night while the group gathered to listen to a lecture, she sat in the back and tried to stick a couple of pieces together.

After much fiddling, the two finally fit and it was clear the skull was more humanlike than baboon. She showed it off like someone who had just solved her first Rubik’s cube.

She had a hominin. But which one?

Ms. Baker gave the skull pieces to Jesse Martin, now a doctoral student at La Trobe University, and Angeline Leece, a paleoanthropologist at the university. They cleaned the skull and painstakingly glued and rebuilt the cranium. Mr. Martin is the team’s go-to expert for such reconstructions, a skill he attributes to an accident he suffered as a child that decreased feeling in his left arm and has allowed him to keep it still for long durations.

To recreate the specimen, called DNH 134, the pair had to hold it together without talking and while controlling their breathing, sometimes for 40 minutes. Any stray cough or sneeze could jeopardize their meticulous work.

“It’s nerve-racking, my heart goes every time,” Dr. Leece said. After several years they fit together more than 150 pieces into the Pleistocene jigsaw puzzle. The two are also now married.

“We’re a couple that is clearly comfortable with awkward silences,” Mr. Martin said.

With each clue they glued together they came closer to figuring out their mystery hominin. Then one day while looking at its long, low skull that had a bony ridge running from the back toward the front, it became clear: They had Homo erectus, the so-called “upright man.”

They also concluded that the specimen was a child, perhaps 3 years old. They named it after Simon Mokobane, a co-author of the study who died from cancer.

During an excavation in 2016, the team was joined by Khethi Nkosi, the current landowner of Drimolen, who pointed out a clue that would become the team’s next big discovery.

“It’s a tooth!” Ms. Baker said.

That tooth would be linked to a find two years later when two students, Amber Jaeger and Eunice Lalunio, moved some loose rocks and dirt from one corner of the cave. Like spotting a shark’s dorsal fin from the beach, Dr. Leece identified a bony crest peeking out from the sediment: They had found another hominin skull top.

Because of its distinct sagittal crest, which served as an anchor for strong cheek muscles, the researchers reasoned the skull belonged to a Paranthropus, similar to Orpheus and Eurydice discovered nearly 25 years earlier. The team recovered a handful of thick bones, which Mr. Martin combined to recreate the skullcap.

They named the specimen after Mr. Nkosi, who had found its tooth during the first dig of his life.

“It’s a blessing and at the same time a humbling experience being part of such a great discovery,” he said. He hopes future research at Drimolen will reveal more clues about humanity’s heritage and help educate the world and change history.

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