The Atapuerca system in northern Spain is a unique place for human evolution. In particular, the cave ‘Sima de los Huesos’ is among the sites with the largest number of hominin fossils. For 30 years, more than 7,500 fossils from 29 individuals have been recovered, representing all parts of the skeleton. They are dated to 430,000 years, which makes them the oldest fossils with Neandertal features. All the individuals belong to the same biological population, which is terribly valuable to analyse their variations, sexual differences and patterns of development.
In 2014 the analysis of the 17 skulls from Sima was published. 7 skulls of the collection had not been published before. This study came 21 years after the description of the first 3 skulls.
The 17 skulls of Sima de los Huesos. Credit: Javier Trueba, Madrid Scientific Films
What are the key conclusions of this study?
1) About the evolution of neandertal features in the Sima materials. Not all the skeleton parts developed simultaneously. The first neandertal features developed were the teeth, the jaw and the face, which suggest some masticatory specialization.
2) Some Neandertal traits are found in the Sima individuals such as:
- a pronounced brow ridge, not sunk over the nose;
- the cheeks projected towards the nose, providing a triangular look to the face;
- the type of engagement of the jaw to the cranium.
3) The braincases are not neandertal-like. Their average brain size is less than modern humans’ and also less than Neandertals’. The brain evolved quite later.
4) The uniformity of the Sima population contrasts with the variation when comparing to other European fossils in the Middle Pleistocene (780 to 130,000 years ago). This can be explained by age and regional variations, and also by interbreeding with archaic populations.
This paper followed another study in 2012 by Chris Stringer, which helped position the Sima fossils outside the taxon Homo heidelbergensis. The Atapuerca team had initially classified the few fossils found in 1993 as Homo heidelbergensis, a species described in 1907 with more primitive features than in Sima. Now this is official: they are no longer Homo heidelbergensis. But what are they exactly? Early Neandertals, an unknown species ancestor of Neandertal…?
Cranium 16 Sima de los Huesos, Atapuerca. Credit: Javier Trueba, Madrid Scientific Films
The amazing collection from Sima de los Huesos will keep growing in the following years – fossils still appear! In 2018 the left side of Cranium 16 was recovered, completing a new skull for this group.
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