摘要
Tooth counts are commonly recorded in fossil diapsid reptiles and have been used for taxonomic and phylogenetic purposes under the assumption that differences in the number of teeth are largely explained by interspecific variation. Although phylogeny is almost certainly one of the greatest factors influencing tooth count, the relative role of intraspecific variation is difficult, and often impossible, to test in the fossil record given the sample sizes available to palaeontologists and, as such, is best investigated using extant models. Intraspecific variation (largely manifested as size-related or ontogenetic variation) in tooth counts has been examined in extant squamates (lizards and snakes) but is poorly understood in archosaurs (crocodylians and dinosaurs). Here, we document tooth count variation in two species of extant crocodylians (Alligator mississippiensis and Crocodylus porosus) as well as a large varanid lizard (Varanus komodoensis). We test the hypothesis that variation in tooth count is driven primarily by growth and thus predict significant correlations between tooth count and size, as well as differences in the frequency of deviation from the modal tooth count in the premaxilla, maxilla, and dentary. In addition to tooth counts, we also document tooth allometry in each species and compare these results with tooth count change through growth. Results reveal no correlation of tooth count with size in any element of any species examined here, with the exception of the premaxilla of C. porosus, which shows the loss of one tooth position. Based on the taxa examined here, we reject the hypothesis, as it is evident that variation in tooth count is not always significantly correlated with growth. However, growth trajectories of smaller reptilian taxa show increases in tooth counts and, although current samples are small, suggest potential correlates between tooth count trajectories and adult size. Nevertheless, interspecific variation in growth patterns underscores the importance of considering and understanding growth when constructing taxonomic and phylogenetic characters, in particular for fossil taxa where ontogenetic patterns are difficult to reconstruct.
摘要译文
齿数通常记录在化石双孔亚纲爬行动物和已用于假设下分类学和系统发育的目的，在齿数差异通过种间变异很大程度上说明。虽然系统发育几乎肯定影响齿计数的最大因素之一，种内变异的相对作用是困难的，并且通常是不可能的，在给定的化石记录测试提供给古生物学家和，作为这样的样本大小，最好使用现存调查模型。种内变异（主要表现为大小相关的个体发育或变异）的齿数已经在研究现存squamates（蜥蜴和蛇），但据了解，在祖龙（crocodylians和恐龙）很差。在这里，我们记录在两种现存crocodylians（鳄鱼mississippiensis和湾鳄），以及一个大的varanid蜥蜴（巨蜥komodoensis）的齿数变化。我们测试假设在齿计数变化主要是由增长推动，从而预测齿计数和大小之间显著相关，以及在偏离于前颌骨，上颌骨和齿骨模态齿计数的频率的差异。除了齿数，我们也记录每个品种牙异速生长和比较这些结果与通过增长齿数的变化。结果显示没有相关性的齿数与尺寸在这里检查，除C.鳄，其示出的一个齿位置损失的前颌骨的任何物种的任何元素。根据这里研究的类群，我们拒绝假设，因为这是显然的变化齿数并不总是显著与生长相关。然而，较小的爬行动物类群节目增加齿数和，增长轨迹虽然目前的样本小，建议齿数轨迹和成人的大小之间潜在的关联。然而，在生长模式间变化突出的考虑和施工时的分类学系统发育的人物，特别是用于矿物分类群，其中个体发育模式很难重建理解增长的重要性。
Caleb Marshall Brown[1]; Collin S. VanBuren[2]; Derek W. Larson[3,*]; Kirstin S. Brink[3]; Nicolás E. Campione[4,5]; Matthew J. Vavrek[6] and David C. Evans[3,6];. Tooth counts through growth in diapsid reptiles: implications for interpreting individual and size-related variation in the fossil record[J]. Journal of Anatomy, 2015,226(4): 322-333