Singleton Michelle
Department of Anatomy, Midwestern University, 555 31st Street, Downers Grove, IL 60515, USA.
J Hum Evol. 2003 Jul;45(1):57-79. doi: 10.1016/s0047-2484(03)00086-1.
Comparative analyses of molar shape figure prominently in Miocene hominoid evolutionary studies, and incomplete understanding of functional and phylogenetic influences on molar shape variation can have direct consequences for the interpretation of fossil taxa. Molar flare is a shape trait whose polarity, phylogenetic distribution, and functional significance have been sources of contention. To clarify the determinants of molar flare variation in the hominoid radiation, a combination of statistical methods was employed to investigate the effects of diet, phylogeny, and geologic age upon several measures of molar shape, to identify interactions among these factors, and to estimate their relative influence. Classic indices of molar crown shape and cusp relief are highly significantly associated with diet and show no clear phylogenetic or temporal patterning. Correlations with diet are insignificant when phylogenetic effects are controlled, a result which is interpreted as an artifact of the distribution of folivory in the Miocene hominoid radiation. Possession of pronounced molar flare was found to be the primitive condition for Miocene hominoids, but molar flare reduction cannot be considered a crown hominoid synapomorphy. Molar flare is strongly correlated with geologic age but differs significantly among dietary categories when the effects of time are controlled. Among contemporaneous taxa, hard-object feeders consistently show the highest levels of flare. Molar flare reduction is hypothesized to arise from realignment of cusp positions to maximize molar shearing and increase working occlusal surface area, while variation in flare among contemporaneous taxa may be due, at least in part, to enamel thickness variation. The pronounced molar flare of Otavipithecus is interpreted as a primitive retention, although alternative dietary and phylogenetic interpretations cannot be excluded. A dramatic reversal of molar flare reduction in Mio-Pliocene hominins is interpreted as a synapomorphy of the crown hominin clade, thus supporting the hominin status of the Lukeino hominine. The last common ancestor of the Pan-Homo clade is predicted to have possessed relatively non-flaring molars, and implications of this hypothesis for early hominin recognition are discussed.
臼齿形状的比较分析在中新世类人猿进化研究中占据显著地位，而对影响臼齿形状变异的功能和系统发育因素的不完全理解，可能会对化石类群的解释产生直接影响。臼齿扩张是一种形状特征，其极性、系统发育分布和功能意义一直存在争议。为了阐明类人猿辐射中臼齿扩张变异的决定因素，采用了多种统计方法来研究饮食、系统发育和地质年代对几种臼齿形状测量指标的影响，以识别这些因素之间的相互作用，并估计它们的相对影响。经典的臼齿冠形状和牙尖 relief 指数与饮食高度显著相关，且未显示出明显的系统发育或时间模式。在控制系统发育效应时，与饮食的相关性不显著，这一结果被解释为中新世类人猿辐射中食叶性分布的人为产物。已发现拥有明显的臼齿扩张是中新世类人猿的原始状态，但臼齿扩张的减少不能被视为冠类人猿的共有衍征。臼齿扩张与地质年代密切相关，但在控制时间效应时，不同饮食类别之间存在显著差异。在同期类群中，硬食者的臼齿扩张水平始终最高。据推测，臼齿扩张的减少是由于牙尖位置重新排列以最大化臼齿剪切并增加工作咬合表面积，而同期类群之间扩张的差异可能至少部分归因于釉质厚度的变化。奥塔维猿明显的臼齿扩张被解释为一种原始保留，尽管不能排除其他饮食和系统发育解释。中新世 - 上新世人类臼齿扩张减少的显著逆转被解释为冠人类分支的共有衍征，从而支持了卢凯诺人属作为人类的地位。预计黑猩猩 - 人类分支的最后一个共同祖先拥有相对不扩张的臼齿，并讨论了这一假设对早期人类识别的影响。
