巨猿牙齿釉质厚度及对食性适应与系统演化的意义

Enamel Thickness of Gigantopithecus blacki and Its Significance for Dietary Adaptation and Phylogeny

步氏巨猿(Gigantopithecus blacki)是更新世时期生活于我国华南地区的一种超大型猿类,它的体态特征和演化分类倍受关注。牙齿釉质厚度在探讨灵长类食性、环境适应以及系统演化方面具有重要意义。本文利用显微CT技术构建18颗巨猿臼齿虚拟模型,测量其釉质厚度。将巨猿釉质厚度与现代人、现生类人猿、古人类、中新世古猿及其他现生灵长类进行比较,从牙齿釉质厚度探讨巨猿的食性适应和系统演化问题。结果发现巨猿的实测釉质厚度是目前所有已知现生和化石灵长类中最厚的,只有傍人、南非早期人属及奥兰诺古猿三种化石灵长类与之接近;如果考虑不同物种牙齿与身体大小的关联因素,相对釉质厚度指数显示巨猿属于"厚"釉质类型,但非"超厚"类型,低于奥兰诺古猿、傍人、南非早期人属;巨猿与某些中新世古猿(如原康修尔猿尼安萨种、非洲古猿)、南方古猿、东非早期人属、亚洲直立人以及现代人、现生卷尾猴的相对釉质厚度指数相近。巨猿的厚釉质特征与其食性和环境适应密切相关,使得牙齿具有非常强的抗磨损功能,能够适应长时间的咀嚼和研磨食物。从釉质厚度的系统演化角度推测,厚釉质应该是人类祖先的特征性状,巨猿有可能是早期人类支系演化过程中的一个特化旁支,同时也不排除巨猿是从某种具有厚釉质的中新世古猿旁支平行演化而来的可能性。

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. bIacki 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.