Quantifying molar tooth shape in primates using geometric morphometrics

采用几何形态计量学方法，对短尾猴磨牙的咬合形态进行了分析。以中央窝为起点，以尖尖、近中窝、远中窝、中央沟与颊舌沟交点、咬合轮廓最突出点为标志。测量了标志物的二维和三维向量，对三个恒磨牙(M1、M2和M3)进行了二维测量，并进行了Procrstes和薄板样条分析。磨牙形状的性别差异很小，但中心大小在两性之间存在显著差异。磨牙的大小和形状的性别差异在磨牙发育较晚的磨牙中比在早期发育的磨牙中更加明显。M_1与M_2形态差异不大，但M_2的形心大小明显大于M_1。上颌第四乳前磨牙(DP4)和第一恒磨牙(M1)的牙合形态变化通过近远中伸长和上颌第四乳前磨牙(DP4)与第一恒磨牙(M1)的联合压缩表现出来。以中心坑为原点，测量了8个地标的三维矢量。DP4的质心大小显著小于M1(P&lt；0.01)。DP4较M1有较浅的窝窝和发达的牙尖突，但牙尖尖在咬合平面上的位置在两个磨牙之间没有差别。

The occlusal shapes of molars in Macaca fuscata fuscata were analyzed by means of geometric morhpometrics. The central pit was selected as the origin, and the following points were selected as landmarks the cusp tips, the mesial and distal pits, and the intersection between central groove and buccal/lingual groove, and the most prominence points of occlusal outline. The two dimensional and three dimensional vectors for the landmarks were measured.Two dimensional measurements were made for the three permanent molars (M1, M2 and M3), and they were analysed by the Procrustes and thin-plate spline analyses. Sexual differences in molar shape were very small, but centroid size was significantly different between the two sexes. Sexual differences in size and shape of the molars were more conspicuous in the later-developed molar than in the early-developed molar. There were small differences between M1 and M2 in shape, but M2 had significantly larger centroid size than M1. The shape change from M1 to M3 is represented by mesiodistal elongation and buc colingual compression of the distal half of the crown.The occlusal shape differences between maxillary fourth deciduous premolar (dp4) and first permanent molar (M1) were analyzed by the thin-plate spline analyze. Three dimensional vectors of 8 landmarks were measured when the central pit was selected as the origin. The centroid size of the dp4 was significantly smaller than the M1 (P<0.01). The dp4 had shallower pits and well-developed metacone than M1, but the location of cusp tips on the occlusal plane did not different among the two molars.