Leonard W R, Hegmon M
Am J Phys Anthropol. 1987 May;73(1):41-63. doi: 10.1002/ajpa.1330730105.
The Australopithecus afarensis dental sample exhibits a wide range of variation, which is most notable in the morphology of the lower third premolar (P3). P3 morphology in the A. afarensis sample ranges from the primitive sectorial extreme in AL 128-23 to the derived, bicuspid (molarized) extreme in AL 333w-1. In this paper, the degree and patterning of variation of the 20 known A. afarensis P3s are examined and the evolutionary implications are discussed. Initially, a series of dental and mandibular metric criteria are evaluated to determine whether this sample may be analyzed as a single species. From the metrics, it is clear that the single species hypothesis cannot be rejected. Next, a series of morphological criteria is devised to measure P3 molarization. Taken as a whole, the A. afarensis P3 sample displays more variation than a sample of modern hominoids (Pan troglodytes) and shows a slight trend toward increased molarization through time. When separated by sex, the A. afarensis sample still displays greater variation than the chimpanzee sample; however, only the male A. afarensis specimens show a trend toward increased molarization. Additionally, the male A. afarensis P3s are more molarized than the female, a pattern that is seen as well (though less markedly) in the chimpanzee sample. The trend toward increased molarization over time indicates selection for grinding in A. afarensis. The sexual differences parallel those seen in the postcrania (cf. Stern and Susman: Am. J. Phys. Anthropol. 60:279-318, 1983), as the females tend to retain the primitive condition, while the males display the derived morphology. Consequently, a model of sexual differences in niche exploitation, with the females exploiting a more arboreal environment, would seem to be supported by both the dental and postcranial evidence.
阿法南方古猿的牙齿样本表现出广泛的变异，这在右下第三前磨牙（P3）的形态上最为显著。阿法南方古猿样本中的P3形态范围从AL 128 - 23中原始的扇形极端形态到AL 333w - 1中衍生的双尖（臼齿化）极端形态。在本文中，对已知的20颗阿法南方古猿P3的变异程度和模式进行了研究，并讨论了其进化意义。首先，评估了一系列牙齿和下颌骨的测量标准，以确定该样本是否可作为单一物种进行分析。从这些测量数据来看，单一物种假说不能被否定。接下来，设计了一系列形态学标准来衡量P3的臼齿化程度。总体而言，阿法南方古猿的P3样本比现代类人猿（黑猩猩）样本表现出更多的变异，并且显示出随着时间推移臼齿化程度略有增加的趋势。当按性别分开时，阿法南方古猿样本仍比黑猩猩样本表现出更大的变异；然而，只有雄性阿法南方古猿标本显示出臼齿化程度增加的趋势。此外，雄性阿法南方古猿的P3比雌性更具臼齿化，这种模式在黑猩猩样本中也有体现（尽管不太明显）。随着时间推移臼齿化程度增加的趋势表明阿法南方古猿存在磨碎食物的选择倾向。性别差异与在颅后骨骼中观察到的情况相似（参见斯特恩和苏斯曼：《美国体质人类学杂志》60:279 - 318，1983），因为雌性倾向于保留原始状态，而雄性表现出衍生形态。因此，牙齿和颅后骨骼的证据似乎都支持了一种生态位利用性别差异的模型，即雌性利用更多的树栖环境。
