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The cranium of the juvenile ape, Lufegpithecus, is in 'excellent' condition, scientists say. (Xue-Ping Ji/Yunnan Institute of Cultural Relics and Archeology)

A team of American and Chinese researchers have uncovered a rare fossil – the cranium of a young ape from a site in Yunnan province, China, that lived between 6 million and 6.5 million years ago, during the Miocene period.

The cranium of the juvenile ape, Lufengpithecus, is only the second relatively complete cranium from a young ape from the Miocene record that has ever been unearthed.

The juvenile crania of apes and hominins are extremely rare in the fossil record, according to Nina Jablonski, professor of anthropology at Pennsylvania State University. Hominins are a group that comprises modern humans, extinct human species and all immediate ancestors, including Australopithecus and the genera Homo.

"The preservation of the cranium is excellent. This is important because all previously discovered adult crania of the species…were badly crushed and distorted," reports Jablonski, who co-authored the findings, published online in the Chinese Science Bulletin. 

Jablonski was part of a team that included scientists from the Yunnan Institute of Cultural Relics and Archeology, Harvard University, Arizona State University, the Zhaotong Institute of Cultural Relics and Cleveland Museum of National History.

Even more noteworthy is that the site, Shuitangba, is just over six million years old, dating near to the end of the Miocene, when apes had become extinct in most of Eurasia.

The fossil provides scientists their best look at the cranial anatomy of the Lufengpithecus, which is in the same lineage as that of present-day orangutans living in Southeast Asia.

Yet, researchers say the cranium shows little resemblance to those of living orangutans, which means that Lufengpithecus represents a late surviving lineage of Eurasian apes but with no clear affinities to current ones.

Researchers say they hope to do further excavations at Shuitangba to find remains of adults, which would allow them to better assess how this particular lineage relates to other fossils and apes living today.