Rising Star Cave (Af. Du Sud): Did Homo naledi bury dead ?
Another twist in the Homo naledi tale: Remains of mysterious early human may have swept into the Rising Star cave from a secret chamber
Homo naledi may shed light on the transition from australopithecines (fossil pictured) - that emerged around four million years ago - to humans. Some of Homo naledi's features, such as its hands, are very similar to those of modern humans. But the species' small brain are more similar to a prehuman group
Researchers who discovered Homo naledi in the Rising Star cave 30 miles (48km) from Johannesburg in South Africa, believe they may have disposed of their dead within the cave.
The alignment of some of the bones suggests they had fossilised where they had been lain just after death.
Scientists leading the excavation, which was published last September, suggested Homo naledi may have dropped their dead down a 'chute' from the surface into the cave.
This would mean a primitive human – which stood a little under 5ft-tall (1.5 metres) and had a brain the size of an orange – may have had a far more advanced culture around death than believed possible.
But new research is suggesting the story may be even more complicated than the anthropologists could have imagined.
Analysis of the sediment and rock suggests there was never a direct opening to the underground fossil site from above.
Indeed, some of the bones found on top of those that were aligned as they would be in the body were far more jumbled, and most of the remains show signs of erosion.
A new theory published in the Journal of Human Evolution instead suggests the 1,550 bones found in the cave, belonging to at least 15 individuals, were brought into the cave through another entrance.
Dr Aurore Vale, an evolutionary biologist at the University of Witwatersrand in Johannesburg, South Africa, said the bones may have initially been in another part of the cave.
She suggests that water instead carried the bones and perhaps even body parts deeper into the cave to where they were found – known as the Dinaledi chamber.
She also points to modifications seen on the fossilised bones that have been attributed to beetles and snails such as the giant African land snail.
While the bones appear to have been damaged by these creatures, they would not have been found living so deep inside the caves as there was no vegetation there for them to live on.
The bones were located in the Rising Star cave system in South Africa's Gauteng province in a remote chamber that can only be accessed via several steep climbs and fissures (arrangement of fossils pictured)
Writing in the journal, she said: 'This raises serious questions about the veracity of the hypothesis that fresh, complete bodies were deliberately disposed into the Dinaledi Chamber.'
The fossils were originally discovered by cavers exploring the subterranean Rising Star caves when they stumbled across part of a skull and some bones in 2013.
Professor Lee Berger, a palaeoanthropologist at the University of Witwatersrand, then led a team to excavate the fossils.
However, the chamber in which they were found was so small and the entrance so tight that Professor Berger had to recruit a group of young women who were small enough to get inside.
Together they filmed, photographed and documented the whole process while Professor Berger directed from the surface.
In total they recovered 1,550 bones which they identified as an entirely new species.
Attempts to date the bones accurately have been difficult and estimates range from 20,000 to two million years old.
Homo naledi has been found to share many features similar to the early Australophithecus species that lived more than three million years ago.
But it also had some distinctive features seen in the Homo species.
There are already some clues about how these early humans may have lived.
Researchers who worked on the excavation say Homo naledi appeared to have unique shoulder features.
Unlike other species of Homo naledi's shoulder blades appear to have been positioned low behind the chest, which would have been better suited to climbing trees than running, according to ScienceNews.
Homo naledi's hands were also built for climbing and gripping stones according to research published in October last years.
A reconstruction of Homo naledi's lower body has also allowed researchers to reconstruct how it would have walked.
In a paper presented at the Annual Meeting of the American Association of Physical Anthropologists in Atlanta earlier this month, Professor Berger and his colleagues said they would have had a bipedal stride much like humans.
Professor Berger said: 'From mid-thigh down it looks like a human - long legs and human like feet.
'It is really a combination we haven't seen before in the fossil record.'
Speaking at the American Association of Physical Anthropologists, his colleague Zach Throckmorton added: 'These characters suggest Homo naledi was well-adapted to a striding bipedal gait.
Peering inside the cave: The chamber, situated down a narrow 40ft (12 metre) chute, measures around 30 feet (9 metres) long and just a few feet wide, National Geographic reported
'Given the anatomy of the upper limb, Homo naledi demonstrates co-existence of both bipedalism and climbing adaptations in one hominin taxon.'
However, following their discovery, perhaps the most controversial claim made by Professor Berger and his colleagues was what Homo naledi were doing in the cave.
Speaking at the time of the announcement in September last year, Professor Berger said: 'This species of non-human hominin was deliberately disposing of its dead.
'Taking a dangerous journey into this deep chamber to place its dead or drop its dead into a place that was inaccessible.
'This is something that prior to this we thought was unique to humans and perhaps identified us but now it doesn't.'