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Pit of Bones Reveals Neandertal Evolution

An international team of scientists has announced that Spain’s “Pit of Bones” archaeological site contains the oldest known fossils with Neandertal traits. Analysis of the skulls at the site has revealed that the hallmark facial features of Neandertals took shape as a first step in their evolution, while their other defining features arose at different times – and not in a single linear sweep.

Published in Science, the researchers say the 17 skulls described, including seven not previously reported, were deposited at Sima de los Huesos about 430,000 years ago. This date clears up debate over the age of the fossils at the site. Previous dates earlier than 530,000 years ago were considered incompatible with morphological and genetic evidence for human evolution of the time.

“This age range is one of the most difficult to date but, rather than relying on a single dating technique, we’ve used six different techniques to produce a robust chronological study which would not have been possible a few years ago,” says Dr Lee Arnold of the University of Adelaide, who conducted dating of the site. “We’ve resolved the age of the fossils at 100,000 years younger than previously reported, which makes them the oldest reliably dated humans to show clear Neandertal morphology.”

So far more than 30 individuals have been recovered from Sima de los Huesos and their skeletons appear to be complete, albeit needing laborious reconstruction. The excavation is difficult, with access limited to a 500-metre crawl through underground caves and a 13-metre abseil down a deep vertical shaft.

The skulls from this population show jaws and teeth that are more typically Neandertal, and upper cranial features more like Homo heidelbergensis, suggesting that the fossils may belong to a new species or subspecies.

The researchers say the Sima de los Huesos population appears to have been part of an early European lineage that includes Neandertals but is more primitive than the later Pleistocene variety.

Furthermore, other fossils from the same geological period are different from those found at Sima de los Huesos, suggesting that there was diversity among different populations in the Middle Pleistocene.

“A picture is emerging of human evolution which is way more complex than has been considered over the past couple of decades,” Arnold says. “Ongoing excavation, DNA analysis and vastly improved chronology are putting together a much more complete story – but we still have many more questions to answer.”