Scientists say human fossils in Siberia have been identified as those of an ancient human group dubbed the Denisovans, cousins of the Neanderthals.

Researchers say the shadowy ancient group lived in Asia from roughly 400,000 to 50,000 years ago and interbred with ancestors of modern inhabitants of New Guinea, The New York Times reported.

Scientists have managed to extract the entire genome of the Denisovans from just one broken finger bone and a wisdom tooth found in a Siberian cave, the newspaper said.

A previous incomplete analysis of Denisovan DNA had suggested the group was far removed from both Neanderthals and humans.

The new findings suggest the ancestors of both the Neanderthals and the Denisovans came out of Africa half a million years ago, with the Neanderthals spreading westward in the Near East and Europe while the Denisovans headed east.

The researchers say the findings confirm there were at least four distinct types of human in existence when anatomically modern humans first left Africa.

Along with modern humans, scientists have identified Neanderthals and a dwarf human species found on the Indonesian island of Flores nicknamed "The Hobbit," the BBC reported.

To this list, experts must now add the Denisovans.

"It is fascinating to see direct evidence that these archaic species did exist (alongside us) and it's only for the last few tens of thousands of years that is unique in our history that we are alone on this planet and we have no close relatives with us anymore," said Svante Paabo of the Max Planck Institute in Leipzig, Germany, who carried out the DNA analysis.