The emergence of a symbolic behaviour: the sepulchral pit of Sima de los Huesos, Sierra de Atapuerca, Burgos, Spain

Sima de los Huesos is one of the most complex Pleistocene sites at Sierra de Atapuerca (Burgos, Spain). This pit has yielded a number of 28 hominids dated around 400 kyr. This is the most complete collection of Middle Pleistocene Homo heidelbergensis around the world. Sima de los Huesos was never a hominid occupation place, since no traces of habitation has been discovered, nor a carnivores net, because there are not herbivores remains. However, it contains a large variety of carnivores, such as foxes, large felidae, wolfs, mustelids, and bears. The presence of these specimens may be explained as several events of natural falling, hibernation and catastrophic death, particularly clear for the bears' case. This may be supported by the fact that all these specimens are present along the whole sedimentary sequence. On the contrary, human remains are mostly concentrated inside a quite discrete sedimentary level, which cannot be explained by any kind of catastrophic nor attritional event, according with the age's profile. The recent finding of an Acheulean handaxe at the Sima de los Huesos cave site casts light on the evolution of human behaviour during the Middle Pleistocene. It is a finely flaked quartzite hanclaxe, which is associated with the hominid assemblage. The particular nature of the deposit involving its taphonomy, palaeontology, and technology points to a symbolic meaning both of the tool and the human accumulation. This would support the hypothesis of human mortuary practices performed at the Sima around 400 kyr ago. This discovery allows us to extend human complex behaviour and symbolism of mortuary rituals 300 kyr earlier than broadly heretofore accepted.