stone tools. He lacked the resources and manpower to continue any further. In 1976, Spanish palaeontologist Trinidad Torres investigated the Gran Dolina for bear fossils (he recovered Ursus remains), but was advised by the Edelweiss Speleological Team to continue at the nearby Sima de los Huesos ("bone pit"). Here, in addition to a wealth of bear fossils, he also recovered archaic human fossils, which prompted a massive exploration of the Sierra de Atapuerca, at first headed by Spanish palaeontologist Emiliano Aguirre but quickly taken over by José María Bermúdez de Castro, Eudald Carbonell, and Juan Luis Arsuaga. They restarted excavation of the Gran Dolina in 1992, and found archaic human remains two years later, which in 1997 they formally described as a new species, Homo antecessor. The holotype is specimen ATD6-5, a right mandibular fragment retaining the molars and recovered with some isolated teeth. In their original description Castro and colleagues posited that the species was the first human to colonise Europe, hence the name antecessor (Latin for "explorer", "pioneer", or "early settler"). The of Pleistocene sediments at the Gran Dolina are divided into eleven units, TD1 to TD11 ("trinchera dolina" or "sinkhole trench"). H. antecessor was recovered from TD6, which has consequently become the most well researched unit of the site. In the first field seasons from 1994–1995, the dig team excavated a small test pit (to see if the unit warranted further investigation) in the southeast section measuring . Human fossils were discovered first by Aurora Martín Nájera; the layer they were found in is nicknamed the "Aurora Stratum" after her. A triangular section was excavated in the central section starting in the early 2000s. Human fossils were also found in the northern section. In sum, about 170 H. antecessor specimens were recovered. The best preserved are ATD6-15 and ATD6-69 (possibly belonging to the same individual) that most clearly elucidate facial anatomy. Subsequent field seasons have yielded about sixty more specimens. The discovered parts of the H. antecessor skeleton are: elements of the face, clavicle, forearm, digits, knees, and a few vertebrae and ribs. In 2007 a mandibular fragment with some teeth, ATE9-1, provisionally assigned to H. antecessor by Carbonell, was recovered from the nearby Sima del Elefante ("elephant pit") in unit TE9 ("trinchera elefante"), belonging to a 20–25-year-old individual. The site additionally yielded stone flakes and evidence of butchery. In 2011, after providing a much more in