Newly identified partial skeletons of "mysterious humans" excavated at two caves in southwest China display an unique mix of primitive and modern anatomical features, scientists say.
"Their skulls are anatomically unique. They look very different to all modern humans, whether alive today or in Africa 150,000 years ago," said evolutionary biologist Darren Curnoe, the lead author of the study, from the University of New South Wales in Australia.
The fossils found at excavation sites in Longlin Cave, in Guangxi Province, and the Maludong Cave, in Yunnan Province, indicate that the stone-aged people had short, flat faces and lacked a modern chin. They had thick skull bones, a rounded brain case, prominent brow ridges and a moderate-size brain.
They were dubbed the "Red Deer Cave" people because scientists say these prehistoric people hunted extinct red deer and cooked them in the cave at Maludong, where four of the five partial skeletal fossils were found.
Whether the Red Deer Cave people are indeed a new species indicating a new evolutionary line or whether they are a very early population of modern humans remains a controversial topic of discussion among scientists.
The team of Australian and Chinese researchers remains cautiously optimistic when it comes to classifying what they have unearthed.
"The evidence is quite fairly balanced at the moment. It's weighted towards the idea that the Red Deer Cave people might represent a new population, possibly a new species," Curnoe said.
Details of the discovery are published in the scientific journal PLoS ONE.
Archeological evidence dates these prehistoric hunters and gatherers to 14,500 to 11,500 years ago, indicating that for a sliver of time in East Asia, the Red Deer Cave people may have shared the landscape with modern-looking people who displayed the beginnings of farming.
Despite Asia being the largest subcontinent, the fossil record for human evolution remains slim. The vast majority of prehistoric archeology has focused on Europe and Africa, scientists say.
"Understanding the fossil records of East Asia is the missing link to our overall understanding of human evolution," Curnoe said.
The Maludong site had actually been excavated the first time by the Chinese in 1989. At that time, several bags of fossils were found, but it was only in 2008 that the site was studied and the remains analyzed by Curnoe and his team of researchers.
The age of the cave sites was determined by collecting sediment samples and tested using radioactive carbon dating.
At the Longlin Cave, the remains of a lower jaw set in a bed of sediment were found by a geologist back in 1979 and rediscovered in a the basement laboratory of one of the Chinese researchers in 2009. The bones first had to be removed from the sediment rock. Then, using a CT Scan 3D, models of the skull were made, showing both the prominent primitive and modern features.
Due to the uncertainty surrounding the human fossil record, paleoanthropologists say, more conclusive DNA testing is required.
Initial DNA testing conducted on the fossils did not show evidence of human DNA, but Curnoe and his team will push forward.
"If we are successful in extracting DNA, it will give us a really accurate understanding of precisely who these people are and where they might fit in the human evolutionary tree," he said.
"We are trying to understand the common story. What unites us all? Where do we come from? In understanding our evolutionary past, this might help us understand where we are today and where we might be going," Curnoe added.