Bathed in darkness, a pre-human child lies in the sunless abyss of a South African cave, never to see light again.
Nearly 250,000 years later, the child’s skull was discovered by researchers from the University of the Witwatersrand (Wits University), South Africa, in the Rising Star Cave System in Johannesburg, representing the first partial skull of an adolescent ancient human relative, Homo naledi.
“Homo naledi remains one of the most enigmatic ancient human relatives ever discovered,” says Professor Lee Berger of Wits University, South Africa, project leader and Explorer at Large for the National Geographic Society.
“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.”
A gold mine of Homo naledi remains
The Rising Star cave System was discovered in 2013, but the first Homo naledi remains were found in the system’s Dinaledi Chamber in 2015. Researchers have since found 2000 fragments, representing more than 20 Homo naledi individuals.
“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,” says John Hawks, a biological anthropologist.
The system is one of the world’s most prolific sites for hominin fossils, and promises insight into the rituals and practices of Homo naledi. One hypothesis is that some of the chambers or passages were treated as a burial ground.
“I do not believe there is another site quite like Rising Star,” says Steve Churchill, a palaeoanthropologist and co-author of the two papers.
“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.”
A Homo naledi child called Leti
The child’s skull was dubbed Leti after the Setswana word letimela, meaning ‘the lost one’. Leti’s gender is unknown, but he or she appeared to be between four and six years of age.
Mysteriously, no other body remains were uncovered beyond the skull, which consisted of 28 bone fragments and six teeth.
“There were no replicating parts as we pieced the skull back together and many of the fragments refit, indicating they all came from one individual child,” says Darryl de Ruiter, a co-author on one of the papers.
“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,” says Juliet Brophy, who led the study on Leti’s skull.
Leti’s brain size was estimated to be around 480 to 610 cubic centimetres.
“This would have been around 90% to 95% of its adult brain capacity,” says Debra Bolter, co-author on the skull study and a specialist in growth and development. “The size of Leti’s brain makes it very comparable to adult members of the species found so far.”
It has been difficult to date the skull, but Tebogo Makhubela, who was part of the discovery, explains that Leti was likely to have lived during the same period as the other Homo naledi discovered in the cave system – they were dated to between 335,000 and 241,000 years ago.
Beyond the Chaos Chamber
Leti’s skull was recovered when researchers explored cramped places 12 metres beyond the Dinaledi Chamber, in a constricted passage only 15 centimetres wide and 80 centimetres long, just beyond and area called the Chaos Chamber.
“The area where Leti was found is part of a spiderweb of cramped passages,” says Maropeng Ramalepa, a member of the exploration team responsible for bringing the remains to the surface.
Marina Elliott, another exploration team member, adds that “this was one of the more challenging sites with hominin fossils we have had to get to in the Rising Star system”.
With no sign of scavenger damage, and no evidence of the skull being washed into such a narrow passage, the researchers don’t know how Leti’s skull came to rest, alone, in such a remote and inaccessible place. Perhaps other members of the species were involved in placing the skull where it was later discovered, or maybe Leti wandered there alone and the rest of the body was later lost to time.
“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,” says Berger.
“It is just another riddle among many that surround this fascinating extinct human relative.”
Deborah Devis is a science journalist at Cosmos. She has a Bachelor of Liberal Arts and Science (Honours) in biology and philosophy from the University of Sydney, and a PhD in plant molecular genetics from the University of Adelaide.
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