JOHANNESBURG, South Africa, Sept. 10 (UPI) -- Researchers have found an ancient burial chamber inside a cave complex in South Africa.
Inside the burial chamber are the remains of what scientists say is a new species of human relative, named Homo naledi. It's the first evidence of a nonhuman species burying its dead.
Rising Star cave has already proven an archaeological and paleontological treasure trove, but the isolation of the Dinaledi chamber -- guarded by an opening just 7.5 inches wide -- kept it largely unexplored by scientists until recently.
Inside the caves, a National Geographic-funded team of scientists found the remains of an ancient humanlike species, a primitive hominin -- not just a few bones, but 1,500 fragments belonging to at least 15 specimens. It's one of the largest finds of its kind.
"We have every age group represented," John Hawks, a member of the team and a paleoanthropologist from the University of Wisconsin, told NPR. "We have newborns; we have children of almost every age; we have adults and old adults."
Homo naledi is part human, part ape. Adults stood roughly five feet tall. While much of its morphological design is primitive -- including a very small skull that housed a very small brain -- its legs and feet are relatively modern. And scientists say its hands feature the most curved fingers they've seen among early hominin species, suggesting the species was capable of advanced tool manipulation.
Researchers don't currently have a reliable method for dating the bones. They could be three million years old. They could be much younger.
Previous research has shown that human evolution did not feature a simple ladder of linear adaptation -- monkey to ape to human -- but produced a variety of experimental hominin species. The discovery of Homo naledi further cements this truth. The question now is: how does Homo naledi and other species marking the transition from ape to human relate to Homo sapiens?
The newly discovered species may also force scientists to reconsider the evolution of tool use.
"If this is an ancient species, like a coelacanthe, that has come down through time and is only tens of thousands, or hundreds of thousands of years old, it means that during that time we had a complex species wandering around Africa, perhaps making tools," Lee Berger, lead scientists on the project and a paleoanthropologist at the University of Witwatersrand in Johannesburg, told The Guardian. "That would make archaeology very difficult, because we aren't going to know who made what."
The discovery, chronicled in two new scientific papers, has already shaken up the evolution of ritual burial. Because the remains are so isolated, researchers concluded that the only way they could have ended up there is if they were deliberately placed. Such behavior wasn't thought to have appeared until modern humans.
"We explored every alternative scenario, including mass death, an unknown carnivore, water transport from another location, or accidental death in a death trap, among others," Berger said in a press release. "In examining every other option, we were left with intentional body disposal by H. naledi as the most plausible scenario."