Other researchers working in the field, such as Prof Stringer, believe that naledi should be described as a primitive human. But he agrees that current theories need to be re-evaluated and that we have only just scratched the surface of the rich and complex story of human evolution.

The bones were found by a spelunker, about 30 miles (48 kilometers) northwest of Johannesburg. The site has yielded some 1,550 specimens since its discovery in 2013. The fossils represent at least 15 individuals. Researchers named the creature Homo naledi (nah-LEH-dee). That reflects the "Homo" evolutionary group, which includes modern people and our closest extinct relatives, and the word for "star" in a local language. The find was made in the Rising Star cave system. The creature, which evidently walked upright, represents a mix of traits. For example, the hands and feet look like Homo, but the shoulders and the small brain recall Homo's more ape-like ancestors, the researchers said.

Lee Berger, a professor at the University of the Witwatersrand in Johannesburg who led the work, said Naledi's anatomy suggest that it arose at or near the root of the Homo group, which would make the species some 2.5 million to 2.8 million years old. The discovered bones themselves may be younger, said Berger, an American.

Discovery Team in South Africa

 Reconstructions of Homo Naledi

This March 2015 photo provided by National Geographic from their October 2015 issue shows a reconstruction of Homo Naledi's face by paleoartist John Gurche at his studio in Trumansburg, N.Y. In an announcement made Thursday, Sept. 10, 2015, scientists say fossils found deep in a South African cave revealed the new member of the human family tree.  

At a news conference Thursday in the Cradle of Humankind, a site near the town of Magaliesburg where the discovery was made, bones were arranged in the shape of skeleton in a glass-covered wooden case.

Fragments of small skulls, an almost complete jawbone with teeth, and pieces of limbs, fingers and other bones were arrayed around the partial skeleton. Berger handed a skull reconstruction to Deputy President Cyril Ramaphosa, who kissed it, as did other VIPs. Berger beamed throughout the unveiling. The researchers also announced the discovery in the journal eLife.

They said they were unable to determine an age for the fossils because of unusual characteristics of the site, but that they are still trying. Berger said researchers are not claiming that neledi was a direct ancestor of modern-day people, and experts unconnected to the project said they believed it was not. Rick Potts, director of the human origins program at the Smithsonian Institution's Natural History Museum, who was not involved in the discovery, said that without an age, "there's no way we can judge the evolutionary significance of this find." If the bones are about as old as the Homo group, that would argue that naledi is "a snapshot of ... the evolutionary experimentation that was going on right around the origin" of Homo, he said. If they are significantly younger, it either shows the naledi retained the primitive body characteristics much longer than any other known creature, or that it re-evolved them, he said. Eric Delson of Lehman College in New York, who also wasn't involved with the work, said his guess is that naledi fits within a known group of early Homo creatures from around 2 million year ago. Besides the age of the bones, another mystery is how they got into the difficult-to-reach area of the cave. The researchers said they suspect the naledi may have repeatedly deposited their dead in the room, but alternatively it may have been a death trap for individuals that found their own way in. "This stuff is like a Sherlock Holmes mystery," declared Bernard Wood of George Washington University in Washington, D.C., who was not involved in the study. Visitors to the cave must have created artificial light, as with a torch, Wood said. The people who did cave drawings in Europe had such technology, but nobody has suspected that mental ability in creatures with such a small brain as naledi, he said. Potts said a deliberate disposal of dead bodies is a feasible explanation, but he added it's not clear who did the disposing. Maybe it was some human relative other than naledi, he said. Not everybody agreed that the discovery revealed a new species. Tim White of the University of California, Berkeley, called that claim questionable. "From what is presented here, (the fossils) belong to a primitive Homo erectus, a species named in the 1800s," he said in an email. At the news conference in South Africa, Berger disputed that. "Could this be the body of homo erectus? Absolutely not. It could not be erectus," Berger said.

A Chronology of Human Evolution:

Ardipithecus Ramidus (4.4 million years ago): Fossils were discovered in Ethiopia in the 1990s. Pelvis shows adaptations to both tree climbing and upright walking.

Australopithecus Afarensis (3.9 - 2.9 million years ago): The famous "Lucy" skeleton belongs to this species of human relative. So far, fossils of this species have only been found in East Africa. Several traits in the skeleton suggest afarensis walked upright, but they may have spent some time in the trees.

Homo Habilis (2.8 - 1.5 million years ago): This human relative had a slightly larger braincase and smaller teeth than the australopithecines or older species, but retains many more primitive features such as long arms.

Homo Naledi (Of unknown age, but researchers say it could be as old as three million years): The new discovery has small, modern-looking teeth, human-like feet but more primitive fingers and a small braincase.

Homo Erectus (1.9 million years - unknown): Homo erectus had a modern body plan that was almost indistinguishable from ours. But it had a smaller brain than a modern person's combined with a more primitive face.

Homo Neanderthalensis (200,000 years - 40,000 years): The Neanderthals were a side-group to modern humans, inhabiting western Eurasia before our species left Africa. They were shorter and more muscular than modern people but had slightly larger brains.

Homo Sapiens (200,000 years - present): Modern humans evolved in Africa from a predecessor species known as Homo heidelbergensis. A small group of Homo sapiens left Africa 60,000 years ago and settled the rest of the world, replacing the other human species they encountered (with a small amount of interbreeding).

Dr Berger describes the descovery of the Homo Naledi: "I was astonished to see how well preserved the bones were. The skull, teeth and feet looked as if they belonged to a human child - even though the skeleton was that of an elderly female. Its hand looked human-like too, up to its fingers which curl around a bit like those of an ape. Homo naledi is unlike any primitive human found in Africa. It has a tiny brain - about the size of a gorilla's and a primitive pelvis and shoulders. But it is put into the same genus as humans because of the more progressive shape of its skull, relatively small teeth, characteristic long legs and modern-looking feet. "I saw something I thought I would never see in my career," Prof Berger said. "It was a moment that 25 years as a paleoanthropologist had not prepared me for." One of the most intriguing questions raised by the find is how the remains got there.