Dr. Becca Peixotto, an American University alumna and anthropology instructor in the College of Arts and Sciences, has again contributed to a major scientific finding involving the human ancestor Homo naledi. Peixotto is part of an international team of researchers, led by Prof. Lee Berger from the University of the Witwatersrand, Johannesburg, South Africa, that has revealed the first partial skull of a Homo naledi child found in the remote depths of the Rising Star cave in Johannesburg.
Describing the skull and its context in two separate papers in the Open Access journal PaleoAnthropology, the team of 21 researchers from Wits University and 13 other universities, including AU, announced the discovery of parts of the skull and teeth of the child that died almost 250,000 years ago when it was approximately 4 to 6 years old. Peixotto, a member of the excavation team, contributed to the paper that describes the context of the area and circumstances in which the skull was discovered.
Researchers found the child in an extremely remote passage of the Rising Star cave system, some 40 feet from the Dinaledi Chamber, the original site of discovery of the first Homo naledi remains that were revealed to the world in 2015.
“The new finding is significant for two reasons: Finding a child skull from 250,000 years ago is rare. Second, this skull was found in a distant, tiny passage away from the main chamber. Its discovery gives us so many questions to ponder: Was it placed there on purpose? Why did Homo naledi go down into this deep, dark passage of the cave?” Peixotto said.
Almost 2,000 individual fragments of more than two dozen individuals at all life stages of Homo naledi have been recovered since the Rising Star cave system was discovered in 2013.
The Lost Child
The skull of the child presented in the current studies was recovered during further work in the cramped spaces of the cave in 2017. The child’s skull was found alone, and no remains of its body have been recovered. The team named the child “Leti” (pronounced Let-e) after the Setswana word “letimela” meaning “the lost one.” Leti’s skull consists of 28 skull fragments and six teeth and when reconstructed shows the frontal orbits, and top of the skull with some dentition.
“Homo naledi remains one of the most enigmatic ancient human relatives ever discovered,” says Berger, project leader and director of the Centre for Exploration of the Deep Human Journey at Wits University and an 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.”
Berger says that work is continuing throughout the cave system and that soon new discoveries are likely to shed further light on whether these chambers and passages are in fact a burial ground of Homo naledi, as the team originally hypothesized.
The Role of Excavation
Peixotto received her Ph.D. in anthropology from AU and is a graduate of the College of Arts and Sciences’ public anthropology master's program. She studied under Prof. Daniel Sayers, honing her skills unearthing artifacts in the Great Dismal Swamp in Virginia and North Carolina, the site where thousands of African Americans who escaped from slavery lived secretly until the end of the Civil War.
In 2013, Peixotto joined Berger’s team. She was also part of the excavation of Neo, a partial skeleton of an adult Homo naledi. While director for the Center of Exploration of the Human Journey at the Perot Museum of Nature and Science in Dallas, Peixotto organized the first exhibit in the U.S. of hominin fossils from South Africa. Two specimens, one being Neo, were on view.
Peixotto has the experience for navigating the cramped, “spiderweb”-like narrow passages of the cave complex, but it’s her archeology expertise that is most crucial in supporting the science of understanding the bones that come up to the surface.
“We have to dig these bones in a way, that once in the lab, researchers can analyze the bones and understand where in the cave they were found. All that location information must be known to researchers as the bones are cleaned and treated in the lab or else the science is faulty,” she explained. “As researchers analyze specimens, I can tell them where they came from, or what was near a specimen when it was found. In a research team of this size, we all bring our pieces of the puzzle together so that we can make hypotheses about the fossils.”
Leti’s brain size is estimated at around 480 to 610 cubic centimeters. “The size of Leti’s brain makes it very comparable to adult members of the species found so far,” says Prof. Debra Bolter, a paper co-author and a specialist in growth and development.
It has yet to be established how old Leti’s remains are. However, since other fossils of Homo naledi were found in the nearby Dinaledi Chamber and dated to between 335,000 and 241,000 years ago, Tebogo Makhubela, part of the geological team investigating the discovery, believes that it is likely that Leti is from a similar period, based on preservation and proximity.
Leti’s remains were discovered in a tight passage that measures only 15 centimeters wide and 80 centimeters long. “This was one of the more challenging sites with hominin fossils we have had to get to in the Rising Star system,” said Dr. Marina Elliott, leader of the excavation team.
With no signs of carnivore damage or damage made by scavenging, and no evidence of the skull having been washed into the narrow passage, the team does not know how Leti’s skull came to rest, alone, in such a remote and inaccessible part of the cave system. The authors hypothesize that it is likely other members of its species were involved in the skull reaching such a difficult place.
“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.”