JOHANNESBURG, South Africa, Feb. 11 (UPI) -- A previously uninvestigated chamber of South Africa's Sterkfontein caves has turned up two new hominin fossils.

The fossils haven't yet been classified but were found among early stone tool-bearing sediments -- deposits dated to 2 million years ago. They are described in the Journal of Human Evolution.


"The specimens are exciting not only because they are associated with early stone tools, but also because they possess a mixture of intriguing features that raise many more questions than they give answers," archaeologist Dominic Stratford, a lecturer at the University of the Witwatersrand, Johannesburg, said in a news release.

Sterkfontein are a series of limestone caves 23 miles northwest of Johannesburg. Its chambers have yielded a variety of hominin fossils from the genera Australopithecus, early Homo and Paranthropus.

Though the newly discovered specimens resemble previously named hominin species, Stratford and his colleagues say they aren't obvious or direct matches. Both possess transitional qualities that may require new classification.

The proximal finger bone is especially intriguing as it is much larger and more robust than other hand bones discovered among plio-pleistocene sites in South Africa. Plio-pleistocene encompasses both the Pliocene and Pleistocene epochs, a geological period ranging from 5 million years ago to 12,000 years ago.

"It is almost complete and shows a really interesting mix of modern and archaic features," Stratford said. "For example, the specimen is markedly curved -- more curved than Homo naledi and is similarly curved to the much older species Australopithecus afarensis."

Similarly, the small tooth, a complete adult first molar, recalls both those of Homo habilis and Homo nadeli.

Two other specimens were also found but have yet to be completely analyzed.

"The two other hominin fossils found are still being studied and further excavations are planned to hopefully find more pieces and expand our understanding of who these intriguing bones belonged to and how they lived and died on the Sterkfontein hill more than two million years ago," said Stratford.