MAGALIESBURG, South Africa (TheBlaze/AP) -- Some scientists say they've discovered a new member of the human family tree, revealed by a huge trove of bones in a barely accessible, pitch-dark chamber of a cave in South Africa. Other researchers though counter that the fossils come from an already known species.
The creature shows a surprising mix of human-like and more primitive characteristics - some experts called it "bizarre" and "weird."
And the discovery presents some key mysteries: How old are the bones? And how did they get into that chamber of the cave, reachable only by a complicated pathway that includes squeezing through passages as narrow as about 7 1/2 inches (17.8 centimeters)?
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. (Mark Thiessen/National Geographic via AP)
The site, about 30 miles northwest of Johannesburg, 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.
This photo provided by National Geographic from their October 2015 issue shows a composite skeleton of Homo naledi surrounded by some of the hundreds of other fossil elements recovered from the Rising Star cave in South Africa, photographed at the Evolutionary Studies Institute of the University of the Witwatersrand in Johannesburg, South Africa. In an announcement made Thursday, Sept. 10, 2015, scientists say the fossils revealed the new member of the human family tree. The expedition team was led by Lee Berger of the university. (Robert Clark/National Geographic, Lee Berger/University of the Witwatersrand via AP)
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, he said.
The researchers announced the discovery Thursday in the journal eLife and at a news conference in the Cradle of Humankind, a site near the village of Magaliesburg. 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.
NPR reported that getting to the fossils for excavation posed a challenge for researchers:
Since he couldn't go, Berger sent in his tall, skinny 16-year-old son. "When he came out after 45 minutes, he stuck his head out. And to tell you how bad I am, I didn't say: 'Are you OK?' I said: 'And?' And he says, 'Daddy, it's wonderful.' "
Berger got funding from the National Geographic Society to excavate the site. And he advertised for research assistants on Facebook — for skinny scientists who weren't claustrophobic. Six women took the job.
They worked in the chamber almost like spacewalkers, communicating with researchers outside, via cameras and about 2 miles of fiber optic cable. The team in the chamber used paintbrushes and toothpicks to gently unearth fossil bones — there were more than 1,550 of them, an incredible treasure trove.
"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.