Prehistoric rib bone. This rib bone was found at the TD-6 level in the Gran Dolina cave in the Sierra de Atapuerca foothills near Burgos, Spain. The TD-6 level (the Aurora stratum) is the oldest that contains hominid remains, and dates to around 780,000 years ago. The remains are those of an extinct member of the human evolutionary tree, either Homo antecessor or Homo erectus. The remains include animal bones and evidence of cannibalism. The limestone caves in these hills, containing many prehistoric fossils and artefacts, have been designated a UNESCO World Heritage Site.