It’s tiny, incomplete, and undeniably awesome. Named “Leti,” this is the first known skull belonging to a Homo naledi child — a fossil that’s shedding new light onto this mysterious group of extinct humans.
The skull fragments, all 28 of them, were found in a tight passage measuring just 5.9 inches (15 cm) wide and 31.5 inches (80 cm) long. So narrow was this passage that researchers had to lie flat and perform a “superman crawl” to pull themselves through, the AFP reports. The cranial remnants and six associated teeth were resting on a limestone shelf located an arm’s reach from the cave floor. Less than 40 feet (12 meters) from this spot is the Dinaledi Chamber — the area within the Rising Star cave system where anthropologists uncovered the first traces of Homo naledi back in 2013.
The cave has since yielded over 2,000 H. naledi fossils, from all stages of life, yet there’s still much to learn about this extinct group of hominins. They date back to an interesting time in human evolution — about 250,000 years ago — when modern humans shared this planet with several other Homo species, such as Neanderthals and Homo erectus.
“Homo naledi remains one of the most enigmatic ancient human relatives ever discovered,” Lee Berger, an anthropologist at the University of the Witwatersrand and a co-author of one of two papers describing the new fossil, both published in PaleoAnthropology, explained in a press release. “It is clearly a primitive species, existing at a time when previously we thought only modern humans were in Africa.”
Scientists aren’t sure how modern humans are related to H. naledi, but we likely share a common ancestor. It’s also not known if H. naledi ventured far beyond the Rising Star cave system, a 1.2-mile (2-kilometre) complex of passages and chambers located near Johannesburg, South Africa. These hominins may have been a small group that branched off the human family tree, or they might’ve been widespread across much of Africa. We don’t know.
The discovery of the first H. naledi child skull is significant, as it could tell us new things about this species, including their rates of growth and development. Anthropologist Juliet Brophy from Louisiana State University, a co-author of both studies, said it’s important to learn about our ancestors and the rates at which they matured because it speaks to a host of anatomical and behavioural changes. Trouble is, we don’t really know a whole lot when it comes to this.
“We have a rough idea,” Brophy explained. “We know the rates are not as fast as a chimpanzee and not as slow as a modern human. With the small number of non-adults in the fossil record, it is very hard to reconstruct,” she said. The rare data being collected in the Rising Star cave system — and now the partial child skull of H. naledi — could allow for the reconstruction of their various life stages.
The scientists found the fossil in 2017, and they’ve named it “Leti,” which is short for Letimela — the Setswana word for “the lost one.” Cause of death could not be determined, as no signs of injury or disease were found on the skull fragments or teeth. Leti was perhaps between four and six years of age when they died, but this estimate assumes a dental growth pattern consistent with modern humans. Sex could not be determined, nor the height or weight of the child. Surprisingly, the team did not date the fossil, prompting me to ask Brophy why.
“The fossil wasn’t dated because we would have to date the fossil itself and dating is destructive. We did not want to lose any of the fossils,” she replied. “We also do not have any reason to suggest that the fossils are from a radically different time than the Dinaledi or Lesedi Chamber fossils. In fact, we hypothesize that they are from a similar time frame as the nearby remains.”
For these reasons, the scientists are content to say that the fossil is somewhere between 236,000 and 335,000 years ago, but Brophy added that the fossil could still potentially be dated in the future.
As the first known skull belonging to a H. naledi child, the scientists could only compare it to other adults of the same species, but it did match in some important respects. Same for the teeth in terms of shape, size, and form. The volume of Leti’s brain was estimated at around 450 to 610 cubic centimeters, which, based on the presumed age, is approximately 90% to 95% the size of an adult H. naledi brain.
One of the more interesting aspects of the discovery is where the fossil was found — a hard-to-reach section of the cave. In the press release, biological anthropologist Marina Elliott, who participated in the initial discovery of H. naledi, said it was “one of the more challenging sites with hominin fossils we have had to get to in the Rising Star system.” How Leti’s skull ended up on that spot remains a mystery.
“However, there is no visible predator or scavenger damage on any parts of the skull, nor is there any evidence that suggests that the sediments surrounding Leti have been moved by water or other means that may have resulted in the depositing of the skull into this remote location,” Brophy told me. “Therefore, we hypothesize that Leti was placed in the passage by another individual.”
The reason for such a particular placement may have something to do with the way ancient peoples treated the dead. Early hominins are known to have placed bodies deep inside of caves, either as some kind of death ritual or to keep them away from animals (or a combination of both, or for reasons unknown). Interestingly, the placement of Leti’s skull is similar to the treatment of an adult H. naledi, nicknamed Neo, whose remains were found in Lesedi Chamber of the Rising Star cave complex.
Looking ahead, the team is hoping to learn more about Leti, such as their diet, an explanation for why some teeth were chipped, and possible relation to other specimens found in Rising Star cave complex.