PMU M3550, an isolated right upper molar (M3) is the first Homo erectus pekinensis ever found. It was discovered in Zhoukoudian Locality 1, locus A, layer 5 by palaeontologist Otto Karl Josef Zdansky. There have been discrepancies in literature as to the exact date of the discovery but various accounts agree that Zdansky found the first tooth during the 1921 summer excavation. A second tooth was also uncovered from his Zhoukoudian collections in the laboratory later on. However, these finds were not announced until a symposium in 1926 [6][2]. Zdansky initially classified the tooth as that of a Homo sp. It was later on reclassified as Sinanthropus pekinensis and eventually as Homo erectus pekinensis [1][7][8]. PMU M3550, an original worn upper M3, belongs to the individual A2 (Locus A, Individual 2) an adult [9][10].