A mysterious ancient human with the lithe body of a ballet dancer has astonished scientists by appearing to show respect for its dead.
Huge numbers of the previously unknown creature's bones were discovered in a remote cave in South Africa that can only be accessed through a "chute" seven inches wide.
Experts believe the slender hominin, whose age is uncertain but may have lived around two million years ago, had used the cave as a burial chamber.
Professor Lee Berger, from the University of the Witwatersrand in South Africa, who led an expedition to the site some 30 miles north-west of Johannesburg, said: "We have just met a new species of human relative that deliberately disposed of its dead.
"The implication of that is significant. Until this moment in history we thought the idea of ritual behaviours directed towards the dead was utterly unique to Homo sapiens. It perhaps identified us; a recent phenomenon that separated us from the animal kingdom.
"We have now seen, we believe, a species that had that the same capacity, and that is extraordinary."
No-other primitive members of the Homo genus, the broad family of "humans", are known to have interred their dead in this way.
Only remains of the creature, named Homo naledi, were discovered in the Rising Star cave which is part of South Africa's Cradle of Humankind world heritage site. Bones of animals were conspicuously absent, and it looked as if the bodies had been placed in the chamber over a long period of time.
In total more than 1,550 individual bone pieces were identified, making it the largest single assemblage of hominin fossils ever discovered in Africa.
'Evidence of ritual body disposal'
So far parts of at least 15 individuals have been recovered, a small fraction of the fossils believed to remain in the chamber. The bones belonged to both sexes and infants as well as elderly individuals, and none bore marks that might have suggested violence or cannabilism.
"We have eliminated the possibility that this was a mass-death," said Prof Berger. "We have eliminated the possibility of a catastrophe. These individuals came in one at a time. They were not eaten by some super-predator."
Quite apart from the evidence of ritual body disposal, Homo naledi is unique in being physically unlike any other primitive human seen to date.
Standing around five feet tall, it had a tiny brain the size of an orange, and shoulders like those of an ape - but also small, human-like teeth, long legs and strikingly modern feet designed for long-distance walking.
Its hands had strong opposable thumbs good for making and using tools, but also long curved fingers clearly adapted for climbing trees.
Professor John Hawks, from the University of Wisconsin-Madison in the US, another member of the international team whose findings are reported in the online journal eLife, said: "We see a creature that has a fascinating mix of characteristics that include unusually human-like features and features comparable with the most primitive members of the human lineage."
Co-author Dr William Harcourt-Smith, from the City University of New York, said H. naledi's foot was extremely human-like "in nearly all aspects".
He added: "It can't grasp with its big toes like gorillas and chimpanzees and other early humans. Critically, it was a stiff foot. This was a very human-like foot - one of the most human-looking in the fossil record."
Many questions about the new human species remain to be answered, most crucially it's age. Normal dating techniques could not be used by the scientists because of the geology of the cave and the lack of animal bones within it. No surviving DNA has yet been extracted from the fossils.
Based on its most primitive features, experts estimate that H. naledi could be as much as 2.5 million years old, close to the "root" of the Homo lineage. However the possibility cannot be ruled out that the creature was a surviving relic and lived at a much later date.
Terry Garcia, chief science and exploration officer at the National Geographical Society, which funded the 2013 expedition, said: "This is a tremendously significant find."
A team of more than 60 cavers and scientists worked together on the discovery. A group of six women petite enough to fit through the cave entrance were selected from a global pool of candidates as "underground astronauts".
Naledi means "star" in Sesotho, a local South African language.
The discovery announcement was relayed in a video link from South Africa to the British Science Festival at the University of Bradford.
Professor Chris Stringer, head of human origins at London's Natural History Museum, said: "The new human species Homo naledi is similar to modern humans in some ways, such as the shape of its hands, wrist and feet. In addition, the deep cave location where the bones were found suggests that they were deposited there by other humans, indicating surprisingly complex behaviour for a 'primitive' human species.
"On the other hand, H. naledi's small brain and the shape of its upper body are more reminiscent of pre-human and very early human species such as Homo habilis, which lived more than 1.5 million years ago. Based on these features, H. naledi could be one of the earliest species of human yet discovered, or a species that retained many features from an earlier stage of human evolution."
Casts of the creature's bones will be put on public display at the Natural History Museum on September 25.