Centre de Recherche en Paléontologie - Paris, CR2P, Muséum national d'Histoire naturelle, CNRS, Sorbonne Université, 8 rue Buffon 75005 Paris, France.
Centre de Recherche en Paléontologie - Paris, CR2P, Sorbonne Université, Muséum national d'Histoire naturelle, CNRS, T.46-56, E.5, case 104, 4 place Jussieu, 75252 Paris cedex 05, France.
Syst Biol. 2021 Oct 13;70(6):1101-1109. doi: 10.1093/sysbio/syab007.
Iterative segments such as teeth or limbs are a widespread characteristic of living organisms. While their proportions may be governed by similar developmental rules in vertebrates, there is no emerging pattern as regards their relation to size. Placental mammals span eight orders of magnitude in body size and show a wide spectrum of dietary habits associated with size and reflected in their dentitions, especially molars. Although variation in size constitutes an important determinant for variation in biological traits, few major allometric trends have been documented on placental molars so far. Molar proportions have been intensively explored in placentals in relation to developmental models, but often at a small phylogenetic scale. Here, we analyzed the diversity of upper molar proportions in relation to absolute size in a large sample of placental species ($n = 299$) encompassing most of the group's dental diversity. Our phylogenetically informed analyses revealed a 2-fold pattern of evolutionary integration among upper molars: while molars covary in size with each other, their proportions covary with the absolute size of the entire molar field. With increasing absolute size, posterior molars increase in size relative to anterior ones, meaning that large-sized species have relatively large rear molars while the opposite is true for small-sized species. The directionality of proportional increase in the molar row exhibits a previously unsuspected allometric patterning among placentals, showing how large-scale variations in size may have influenced variation in dental morphology. This finding provides new evidence that processes regulating the size of individual molars are integrated with overall patterns of growth and calls for further testing of allometric variation in the dentition and in other segmental series of the vertebrate body. [Dentition; evolution; model; phylogeny; segmentation; size.].
迭代段，如牙齿或肢体，是生物的普遍特征。虽然它们的比例可能受到脊椎动物类似的发育规则的控制，但它们与大小的关系却没有出现明显的模式。胎盘哺乳动物的体型跨度为 8 个数量级，具有广泛的与体型相关的饮食习惯，这些习惯反映在它们的牙齿中，尤其是臼齿上。尽管大小的变化是生物特征变化的一个重要决定因素，但到目前为止，在胎盘哺乳动物的臼齿上很少有记录到主要的比例变化趋势。臼齿的比例与发育模型的关系在胎盘哺乳动物中得到了深入研究，但通常是在小的系统发育尺度上。在这里，我们分析了大量胎盘物种（n = 299）中上颌臼齿比例与绝对大小的关系，这些物种涵盖了该组牙齿多样性的大部分。我们的系统发育信息分析揭示了上颌臼齿之间进化整合的 2 倍模式：虽然臼齿在大小上彼此相互变异，但它们的比例与整个臼齿区域的绝对大小相关。随着绝对大小的增加，后臼齿相对于前臼齿增大，这意味着大型物种具有相对较大的后臼齿，而小型物种则相反。在摩尔列中比例增加的方向性表现出了胎盘动物中以前未被察觉的比例模式，显示了大规模的大小变化如何影响牙齿形态的变化。这一发现为调节单个臼齿大小的过程与整体生长模式相结合提供了新的证据，并呼吁进一步测试牙齿和其他脊椎动物身体分段系列中的比例变化。[牙齿；进化；模型；系统发育；分段；大小。]
