Rising Star cave (Af. Du Sud): First fossil of Homo naledi child found
Ashley Strickland, CNN
For hundreds of thousands of years, the fossil of a small child has been hidden in the darkness of South Africa's Rising Star cave. The skull, from a child that was 4 to 6 years old at the time of death, is the first known to belong to an ancient human relative called Homo naledi.
The child likely lived between 236,000 and 335,000 years ago, which is when other remains from the cave have been dated.
"This is the first partial skull of a child of Homo naledi yet recovered and this begins to give us insight into all stages of life of this remarkable species," said Juliet Brophy, lead author of the study analyzing the skull, in a statement. Brophy is an associate professor at Louisiana State University and honorary research affiliate at the University of the Witwatersrand.
It's unknown if the child was male or female, but researchers have nicknamed the fossil "Leti" and often refer to Leti as female. The name is short for "letimela," which means "the lost one" in the Setswana language, one of South Africa's 11 official languages.
This is a reconstruction of the Leti skull found in the Rising Star cave system outside Johannesburg, South Africa.
The research team that located the partial skull, which was assembled from 28 fragments and six teeth, was led by Lee Berger, a professor at the University of the Witwatersrand, who announced the discovery of the previously unknown Homo naledi species in 2015. There is no trace of the rest of Leti's body.
It's unknown how Leti died, and her age is based on her teeth. "But at present we have not established exactly how fast Homo naledi children grew, so it is possible she was younger," the researchers said.
Leti was found in 2017 in what is described as an incredibly remote passage of the Rising Star Cave System, about 39 feet (12 meters) from where Berger's team discovered the first Homo naledi remains in the Dinaledi Chamber. The cave system is located in the Cradle of Humankind, a UNESCO World Heritage Site in South Africa's Gauteng province.
But how did Leti's skull come to be in the cave? The fragments of her cranium were retrieved from a limestone shelf in an extremely narrow passage only 5.9 inches (15 centimeters) wide by 31.4 inches (80 centimeters) in length. The shelf was about 31 inches above the current cave floor. It's possible that her skull was placed there on purpose. Researchers are still investigating if the cave system is truly a burial ground for Homo naledi.
Previously, it was believed only modern humans buried their dead.
Leti's discovery is similar to how Neo, the remains of an adult male Homo naledi from another chamber, were discovered in a narrow passage.
"The area where Leti was found is part of a spiderweb of cramped passages," said Maropeng Ramalepa, a member of the exploration team responsible for bringing the remains to the surface, in a statement.
Excavating Leti was "very difficult," according to Marina Elliott, cave location study author, leader of the excavation team, and one of the original members of the all-female "Underground Astronauts" in the first expedition to uncover Homo naledi.
"This was one of the more challenging sites with hominin fossils we have had to get to in the Rising Star system," Elliott said in a statement.
Leti's skull showed no signs of damage made by a carnivore or scavenging, and there is no evidence that water may have carried the skull into the passage.
"The discovery of a single skull of a child, in such a remote location within the cave system adds mystery as to how these many remains came to be in these remote, dark spaces of the Rising Star Cave system," said Berger, director of the Centre for Exploration at Wits University and an explorer at large for the National Geographic Society, in a statement. "It is just another riddle among many that surround this fascinating extinct human relative."
Getting to know Homo naledi
The remains of juveniles are often thin and fragile, so the researchers feel fortunate for the opportunity to learn more about what Homo naledi children were like.
This image shows Leti's unemerged permanent premolar teeth.
After reassembling the partial skull, the scientists compared it to ancient individuals of a similar size, like the primitive human relative Australopithecus africanus. Based on their analysis, Leti's brain case would have supported a brain that was around 177 to 240 cubic inches (450 to 610 cubic centimeters), or about 90% to 95% of the size her brain would be had she reached adulthood.
That would make it similar to others of her species.
Homo naledi was a strange mosaic of the ancient and the thoroughly modern. Naledi's brain was no bigger than an orange, scientists say, and its hands are superficially human-like. But, the finger bones are locked into a curve -- a trait that suggests climbing and tool-using capabilities. And researchers think they lived alongside modern humans.
"Homo naledi remains one of the most enigmatic ancient human relatives ever discovered," Berger said. "It is clearly a primitive species, existing at a time when previously we thought only modern humans were in Africa. Its very presence at that time and in this place complexifies our understanding of who did what first concerning the invention of complex stone tool cultures and even ritual practices."
Since the initial discovery of Homo naledi in 2013, the team has recovered nearly 2,000 fragments from more than two dozen individuals at varying stages of life.
"This makes this the richest site for fossil hominins on the continent of Africa and makes naledi one of the best-known ancient hominin species ever discovered," said John Hawks, Vilas-Borghesi Distinguished Achievement Professor at the University of Wisconsin-Madison and lead author of a previous study on the Neo fossil skeleton, in a statement.
A cave of secrets
Rising Star has more than 1.2 miles (2 kilometers) of chambers and passages. And the question remains, if Homo naledi didn't bury their dead, how did their remains reach this maze-like system of caves?
Some have questioned if there are alternate entry routes to the chambers, allowing for the remains to find their way inside the cave, since the fossils all lack evidence of being dragged in by carnivores, scavengers, or being deposited by shifting sediment or running water.
The only known route to reach the Dinaledi Chamber is called the Chute, a fissure that's 39.3 feet (12 meters) high, which has narrow points only 7 inches (18 centimeters) wide.
During their investigation, the researchers searched for any other ways to access this chamber.
"Exploration of the narrow passages within the Dinaledi Subsystem involves considerable effort, navigating areas with irregular floors and walls, numerous obstructions and fissures less than 30 centimeters (11.8 inches) wide," the authors wrote.
Their exploration revealed that the Chute is the only way in -- and four new fossil deposits exist in "extremely difficult and remote" areas that could contain new Homo naledi fossils. This intriguing evidence suggests that the burial hypothesis is increasingly more likely.
"I do not believe there is another site quite like Rising Star," said palaeoanthropologist Steve Churchill, Duke University professor and coauthor on both papers, in a statement. "This is now the third locality we have described from this system with naledi remains, and we know through exploration that there are other localities."