Skulls discovered at key Spanish site point to Neanderthals’ origins

Unearthing of 430,000-year-old fossils at Atapuerca sheds light on our cousins’ ancestors

Researchers working inside Sima de los Huesos, in Atapuerca (Burgos).
Researchers working inside Sima de los Huesos, in Atapuerca (Burgos).javier trueba-madrid scientific films

No paleontology site in the world comes even close to containing such a wealth of information as the Sima de los Huesos (Bone Pit) in Atapuerca, in the northern Spanish province of Burgos.

If just one hominid tooth represents a major discovery at any site, this cave has yielded 17 skulls, some of them intact, and nearly 6,500 fossils dating back 430,000 years.

“The men at Sima de los Huesos are the beginning of Neanderthal evolution, they are the oldest in the lineage,” explains Ignacio Martínez, a lecturer at Alcalá de Henares University and a researcher at Atapuerca.

Sima de los Huesos has been described as “a paleontological treasure”

“The traits of their faces and their teeth are typical of Neanderthals, while the shape of their skulls is still archaic,” he continues. “Everything suggests that the evolution towards the Neanderthal lineage is related to chewing; we are seeing modifications relating to the intensive use of their incisors, as though they used their teeth as a third hand to help with multiple tasks.”

On Friday, the team published a paper explaining its discoveries in US journal Science. The article reviews the latest discoveries at Sima de los Huesos, including seven new skulls, which bring the total to 17.

The journal notes that this is the greatest collection of ancient human fossils ever recovered at a dig, and that their analysis sheds light on the origin and evolution of the Neanderthals.

“Based on their morphology, we think that the people of Sima de los Huesos were part of the Neanderthal lineage, although they don’t have to necessarily be direct ancestors of the typical Neanderthals,” writes Juan Luis Arsuaga, co-director of the dig.

Humans were already in Atapuerca 1.2 million years ago, as shown by fossils found at a spot known as El Elefante. Around 500,000 years ago, a group settled at Sima de los Huesos. This population was “like a maternal aunt to subsequent Neanderthals, not necessarily their mother,” says Martínez. “What is clear is that there was not one single human species at the time, but several coexisting in that territory.”

Neanderthals lived in Europe from 200,000 years ago until 30,000 or 40,000 years ago, when they became extinct. Their territory had been taken over by modern humans who came in from Africa and the Middle East.

While there was some interbreeding, “both groups already had several incompatible traits,” notes Jean Jaques Hublin, an expert at the Max Planck Institute of Evolutionary Anthropology, in Science magazine.

Hublin described Sima de los Huesos as “a paleontological treasure.”

Reconstructing the puzzle

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“The fossils at Sima de los Huesos… It’s like having 28 puzzles made up of 206 pieces each,” says Ana Gracia, a specialist in reconstructing the bones of the Atapuerca fossil collection. There are at least 28 individuals whose bones have been partly recovered from the site, and each human skeleton has 206 bones.

Gracia, a researcher at Alcalá de Henares University, has spent nearly 30 years working at Sima de los Huesos, and she describes the hominids as her “other family.” She has seen the trove grow from the initial dozen found in the 1980s to more than 6,500 today.

“You try to keep track of all the fossils in your head to figure out who each one might belong to,” she explains.