Morris Philip J R, Cox Philip G, Cobb Samuel N
Hull York Medical School, University of Hull, Hull HU6 7RX, UK.
Department of Archaeology and Hull York Medical School, University of York, York YO10 5DD, UK.
R Soc Open Sci. 2019 Mar 27;6(3):181317. doi: 10.1098/rsos.181317. eCollection 2019 Mar.
All rodents possess a single pair of enlarged incisors that grow throughout life. This condition (diprotodonty) is characteristic of Rodentia, but is also found in other mammals such as lagomorphs, hyraxes, the aye-aye and common wombat. This study surveyed lower incisor morphology across extant diprotodonts to examine shape variation within and between rodents and other diprotodonts, and to determine if tooth shape varies in a manner predictable from mechanics. Six linear and area variables were recorded from microCT scans of the mandibles of 33 diprotodont mammals. The curvature of the rodent lower incisors, as measured by the proportion of a circle it occupies, was shown to vary between 20 and 45%, with non-Glires taxa falling outside this range. Relative lengths of the portions of the incisor within and external to the mandible were not significantly correlated when the overall size was taken into account. Cross-sectional geometry of the incisor was significantly correlated with the external length of the incisor. Overall, incisor morphology was shown to vary in a way predictable from ecology and mechanics, in order to resist bending. Among non-rodents, lagomorph incisors closely resemble those of rodents, and, relative to rodents, hyrax and wombat incisors are somewhat smaller but aye-aye incisors are much more extreme in morphology.
所有啮齿动物都有一对不断生长的增大的门牙。这种情况（双门齿型）是啮齿目的特征，但在其他哺乳动物中也有发现，如兔形目动物、蹄兔、指猴和袋熊。本研究调查了现存双门齿动物的下门牙形态，以检查啮齿动物与其他双门齿动物内部和之间的形状变化，并确定牙齿形状是否以可从力学预测的方式变化。从33种双门齿哺乳动物下颌骨的显微CT扫描中记录了六个线性和面积变量。啮齿动物下门牙的曲率，以其所占圆的比例来衡量，显示在20%到45%之间变化，非灵长总目类群落在这个范围之外。当考虑总体大小时，下颌骨内外门牙部分的相对长度没有显著相关性。门牙的横截面几何形状与门牙的外部长度显著相关。总体而言，门牙形态显示出以可从生态学和力学预测的方式变化，以抵抗弯曲。在非啮齿动物中，兔形目动物的门牙与啮齿动物的门牙非常相似，相对于啮齿动物，蹄兔和袋熊的门牙稍小，但指猴的门牙在形态上更为极端。
