Fossils retrieved from an underground cave in South Africa may represent a previously unknown species of the human genus, Homo.
The fossils come from at least 15 individuals recovered from a 30-meter-deep pit, says a team led by paleoanthropologist Lee Berger of the University of the Witwatersrand in Johannesburg. The skeletal remains display a novel mix of humanlike features and more apelike traits characteristic of 2-million- to 4-million-year-old hominids from the genus Australopithecus, the researchers report September 10 in eLife.
Berger and colleagues assign the finds to a new species, Homo naledi. The word naledi means star in South Africa’s Sotho language. “We don’t know how old these fossils are,” Berger said September 9 during a news conference. “But based on its anatomy, H. naledi clearly sits near or at the root of the Homo genus.”
Some researchers are skeptical. H. naledi seems to be a new species, but without dates its evolutionary significance is unknown, says paleoanthropologist Carol Ward of the University of Missouri in Columbia.
The hominid remains were recovered in November 2013 and March 2014, shortly after two cave explorers discovered the fossils and alerted Berger. His team recruited six slender researchers, who were also experienced cave explorers, to climb down a narrow, 90-meter-long vertical passage to a pit nicknamed Dinaledi Chamber.
No age estimates have been obtained for the 1,550 H. naledi fossils found on the cave floor and in an excavation. The fossils lay in soft sediments that have partly mixed together over time, obscuring the bones’ original location. No fossils of other animals were found near the hominid remains, depriving researchers of another clue to H. naledi’s age.
If the fossils date to more than 2 million years ago, H. naledi would become one of the oldest members of the human genus (SN: 4/4/15, p. 8). A date younger than 2 million years would support the idea that many Homo species, as well as many Australopithecus species (SN: 8/10/13, p. 26), once coexisted in Africa.
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Berger and his colleagues estimate that H. naledi stood an average of about 1.5 meters (5 feet) tall and weighed around 45 kilograms (almost 100 pounds).
Many skull features, including prominent brow ridges, link H. naledi to ancient Homo species, the researchers say. So do small teeth and jaws.
Long, relatively light leg bones and humanlike ankles and feet indicate that H. naledi had a smooth, upright gait. The hominid’s wrists and hands also look much like those of early Homo species.
In contrast, H. naledi’s shoulder, rib cage, pelvis, upper leg and curved fingers enabled proficient tree climbing, as in Australopithecus species, the investigators say. H. naledi also had an Australopithecus-sized brain, about the size of an orange.
Paleoanthropologists’ opinions about the finds vary. “Despite the small brain, this new species is clearly part of the genus Homo because of the way the skull is built,” says Fred Spoor of University College London. Spoor doubts H. naledi was a direct ancestor of modern humans.
Christoph Zollikofer of the University of Zurich agrees that the fossils probably represent Homo. But he thinks the bones look “strikingly similar” to nearly 1.8-million-year-old Homo erectus fossils found in West Asia (SN: 11/16/13, p. 6). The South African hominids may have belonged to H. erectus and evolved a few skeletal innovations, such as distinctive hands, while living at the bottom of the continent, Zollikofer suggests.
Australopithecus-like features of the teeth and lower body raise doubts about whether the new finds come from an early Homo species, asserts Susan Antón of New York University. The fossils, she says, “are fabulous and a bit confusing.”
In another provocative analysis, described September 10 in a second eLife paper, Berger’s group suggests that H. naledi intentionally dropped dead comrades down the passage into the underground chamber, perhaps in some type of ritual. Fossil and soil studies led by geologist Paul Dirks of James Cook University in Townsville, Australia, rule out some other explanations for the hominids’ presence there, such as being washed in by floods or dragged in by predators.
The possibility that H. naledi deliberately disposed of bodies in the cave is “interesting and intriguing, but will also be controversial,” Spoor says.