SEATTLE, May 11 (Xinhua) -- An international team of researchers has found additional remains of a new human species, Homo naledi, in a series of caves northwest of Johannesburg, South Africa.
The find includes the remains of two adults and a child in the Lesedi Chamber of the Rising Star Cave system, expanding the fossil record originally reported from a different chamber of the cave in 2015.
Details of the new discovery are published this week in two papers in eLife, along with another paper from the research team that pinpoints an age range of the original Rising Star fossils, which comprised 15 different individuals.
Those remains of a primitive, small-brained human ancestor that researchers dubbed Homo naledi were found in Rising Star's Dinaledi Chamber and are believed to be between 236,000 and 335,000 years old, meaning that Homo naledi may have coexisted, for a period of time, with Homo sapiens, the species of modern humans.
Researchers haven't yet been able to date the fossils from the Lesedi Chamber, which include one of the most complete skeletons of an early human found to date. The excavation of that chamber, researchers believe, provides further evidence that this early human species deliberately disposed of its dead in these remote, hard-to-reach caves.
The hypothesis generated criticism when the Dinaledi discovery was first reported, with some researchers pointing to other potential causes and timelines for the deposition of the bones. The Rising Star team maintains that the lack of animal remains found at the site, and the absence of injury to or erosion of the human fossils, rules out predatory or natural causes of accumulation.
"What we're seeing is the importance of compromise in our own genus," Elen Feuerriegel, a postdoctoral researcher in the Department of Anthropology at the University of Washington (UW) who was one of the members of the team that excavated both Dinaledi and Lesedi, was quoted as saying in a news release.
"The fact that Homo naledi has a similar hand and wrist to Homo sapiens, but a brain one-third the size of ours, shows that they may not have needed as much brainpower to do complex things. The process of human evolution is more complicated than we thought," Feuerriegel said.
To establish an age of the Dinaledi fossils, the research team, which involved 52 members from nearly three dozen institutions, used a combination of techniques for both the bones and the surrounding sediments, including uranium series and electron spin resonance dating to examine teeth. Since other Australopithecus fossils have been found not far from the Rising Star Cave system, researchers had initially expected the Dinaledi fossils to be closer in age to those older ancestors -- not from as recently as 236,000 to 335,000 years ago.
"We can no longer assume that we know which species made tools, or even assume that it was modern humans that were the innovators of some of these critical technological and behavioral breakthroughs in the archaeological record of Africa," said Professor Lee Berger of the University of the Witwatersrand in South Africa, who assembled the team that first explored the Rising Star system in 2013 and is an author on the latest papers.
"If there is one other species out there that shared the world with 'modern humans' in Africa, it is very likely there are others. We just need to find them."
Further excavation of the cave system is planned, an undertaking that requires excavators who can squeeze through passages as narrow as 7.5 inches, or 19 centimeters, and spend hours 100 feet, or about 30 meters, underground.
