Abstract: In is difficult to distinguish Ml from M2 of Gigantopithecus through any single trait such as crown length and breadth, as showed by their distributions.
The present paper applies the method of principal component analysis to distinguish first upper molars from second ones, and the variables used are crown length, crown breadth and protocone length index (newly defined). The results show the existence of two categories in M1,2. A reasonable explanation for this is that they represent M* and Ma respectively. *The role played by protocone length (mesiodistal diameter) to discriminate between M1 and M2 of Gigantopithecus becomes clear due to the principal component analysis. This trait is likely to be of significance for other high primates in the same aspect.
The distinguishing of lower molars is based on the observation of the three Gigantopithecus mandibles with teeth as well as the over 100 isolated teeth. Two series of ellipses in the coordinate chart of crown length and breadth represent the ranges of different sample distribution probabilities of Mi and M2, respectively, and disesiminatory lines are drawn between and M2.

Key words: Gigantopithecus; High Primates; Molar; Principal component ana_x001F_lysis; Distribution probability