The discovery of an ancient tooth has lead researchers to believe that distant human relatives called the Denisovans had the chance to co-habituate with humans and Neanderthals thousands of years ago.

Before the tooth was discovered, the existence of Denisovans was only based on another tooth and a tiny finger bone that researchers concluded belonged to the same man but from a species unknown to science. Since the body parts were found in the Denisova cave in 2008, scientists decided to name the species Denisovans, according to Popular Science.

"It's an amazing place because it's actually the only place in the world where we know that three different groups of humans with very different histories all lived," said Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology and researcher on the study, USA Today reported.

With the DNA taken from the new ancient tooth, which was also found in the Denisova cave, scientists are able to determine that the species ranged across Asia for tens of thousands of years and was actually a big population.

The analysis also showed that the Denisovans interbred with modern humans, as about five percent of the DNA of native Papua New Guineans and Australians and 0.2 per cent of the DNA of Asians and Native Americans is Denisovan, CBC News reported.

With this latest discovery, scientists now have a better chance of properly placing the Denisovans on the human family tree.

The research was published in the Proceedings of the National Academy of Sciences.