K11337:3 is a single left lower molar (M1) fossil found by Swedish palaeontologist Anders Birger Bohlin on 16 October 1927, in Zhoukoudian Locality 1, locus A, layer 5. It serves as the holotype specimen for Sinanthropus pekinensis since Black [1] used this single specimen to create a new genus and species name for Peking Man. Black was able to do this in part because Zdansky had already found two human teeth from the Zhoukoudian deposits prior [2][3]. Sinanthropus pekinensis has ceased to be used as a scientific name and has been replaced by Homo erectus pekinensis [4][5]. 

Unfortunately in 1941, on the outbreak of the Second Sino-Japanese War,  this specimen together with the whole collection excavated from 1928 to 1937 was lost during transport to the United States for safekeeping. This includes numerous remains of Peking Man (> 40 individuals) including five skulls [6][7][8]. Only the two diagnostic teeth found by Zdansky and a few crates of Zhoukoudian material sent to Uppsala University in the 1920s remain [9].