Abstract: Gigantopithecus blacki, a large Pleistocene hominoid from South China and Vietnam, is a very special taxon in any discussion of primate dietary proclivity and evolutionary phylogeny. In this study, 18 teeth of G. blacki, unworn or slightly-worn, are reconstructed using micro-CT in order to measure enamel thickness, and compared with extant and extinct humans and other primates.? We ?find ?that,? in? absolute? dimensions,? G. blacki has the thickest enamel thickness of any fossil or extant primates, while Paranthropus, early Homo and Ouranopithecus macedoniensis possess relatively closer values with it. With considerations of body and tooth size, the enamel measurements indicate that G. blacki belongs to a category of “thick-enamel” primate along with modern humans, Cebus, Australopithecus, East African Early Homo, Asian Homo erectus and some Miocene fossil apes (eg Proconsul nyanzae and Afropithecus turkanensis), but thinner than South African early Homo, Paranthropus and Ouranopithecus macedoniensis. The extremely thick enamel of G. blacki molars are evidently well used for grinding and crushing for a long period. The dietary proclivities may primarily focus on tough or fibrous vegetation. Human ancestors probably have thick enamel. G. blacki may be a side branch of hominids during the evolution. Meanwhile, G. blacki can be also evolved from one branch of Miocene fossil ape whose teeth enamel is thick. The thick enamel, common characteristic of G. blacki and human, is the result of parallel evolution.

Key words: Gigantopithecus blacki; Enamel thickness; Phylogeny; Functional adaptation; Micro-CT