Fossilised frontal bone from a child's skull. Fragments of a 12-year-old child's cranial bone being pieced together by a palaeontologist. These pieces, which date back approximately 800,000 years, were found in level TD6 of the Gran Dolina site in 1994 and are part of a collection that led to the naming of a new hominid (a type of early human) species, Homo antecessor. Gran Dolina is one of several archaeological sites in Sierra de Atapuerca, Spain, that have been studied over the past century, leading to a massive advancement in the understanding of human evolution. In 2000, Sierra de Atapuerca was made a world heritage site by UNESCO.