The genome of a cave-dwelling girl from 80,000 years ago has been analyzed in such detail it's known she had brown hair, eyes and skin, German researchers say.

The cave dweller was a Denisovan, named because bone fragments were found in Siberia's Denisova cave in 2010.

Denisovans were evolutionary cousins of the Neanderthals before both groups died out about 30,000 years ago.

Researchers at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, analyzed a small finger bone to extract DNA information about the previously unknown group of ancient humans.

"This is an extinct genome sequence of unprecedented accuracy," Matthias Meyer, chief researcher on the study, told the BBC.

Comparison of the girl's genome with that of Neanderthals and 11 modern humans from around the world allowed researchers to identify the gene changes that make modern humans different from the two groups of extinct humans, he said.

"To me the most exciting thing is having a good genome from our very closest extinct relatives which we can now compare ourselves to.

"It's a catalog of what makes everyone on the planet unique compared with our closest extinct relatives," he said.