Prehistoric bear jaws. These fossil jaw bones are from an extinct bear species (Ursus dolinensis). They were found in 1991 and 1996 at the TD-4 level in the Gran Dolina cave in the Sierra de Atapuerca foothills near Burgos, Spain. This level is around 800,000 years old. The limestone caves in these hills, containing many prehistoric fossils and artefacts, have been designated a UNESCO World Heritage Site.