Johannesburg: Scientists have discovered a new species in the human family tree - a small creature with a tiny brain - after examining a huge haul of fossilised bones found in a dark chamber of a South African cave, raising intriguing questions about our evolutionary past.
The discovery of fossils of 15 individuals, consisting of 1,550 bones, represents the largest fossil hominin find on the African continent, researchers said.
The finding also indicates that these individuals may have been capable of ritual behaviour.
"We found adults and children in the cave who are members of genus Homo but very different from modern humans," said Charles Musiba, associate professor of anthropology at University of Colorado Denver.
The discovery was made inside the Rising Star Cave in the Cradle of Humankind World Heritage Site in South Africa.
"They are very petite and have the brain size of chimpanzees," Musiba said.
"The hand has human-like features for manipulation of objects and curved fingers that are well adapted for climbing," said Caley Orr, assistant professor at the University of Colorado School of Medicine.
The new species has been dubbed Homonaledi after the cave where it was found - naledi means 'star' in the local South African language Sesotho.
The bodies appear to have been deposited in the cave intentionally, the researchers said. Scientists have long believed this sort of ritualised or repeated behaviour was limited to humans.
The team of 35 to 40 scientists was led by Lee Berger, research professor in the Evolutionary Studies Institute at the University of Witwatersrand in South Africa.
"There are potentially hundreds if not thousands of remains of H naledi still down there," said Berger.
The exact position of the species in our family tree is unknown, researchers said. There is an assumption that any new group of fossils must belong to an existing species.
"While Homo(naledi) shares aspects of cranial and mandibular morphology with Homohabilis, Homorudolfensis, Homoerectus, MP Homo and Homosapiens, it differs from all of these taxa in its unique combination of derived cranial vault, maxillary, and mandibular morphology," researchers said.
The study suggests that Homonaledi most closely resembles Homoerectus with its small brain and body size. Yet it also resembles Australopithecus which highlights its own uniqueness.
The researchers still do not know the exact age of the fossil site.
"If these fossils are late Pliocene or early Pleistocene, it is possible that this new species of small-brained, early Homorepresents an intermediate between Australopithecus and Homoerectus," researchers said.
But if the fossils are more recent, they theorise, it raises the possibility that a small-brained Homo lived in southern Africa at the same time as larger brained Homo species were evolving.
The finding was published in the journal eLife.