Data from: Axial growth gradients across the postprotaspid ontogeny of the Silurian trilobite Aulacopleura koninckii

Recent morphometric analysis revealed a juvenile (meraspid) axial growth gradient in the trunk of the ~429 Myr old trilobite Aulacopleura koninckii that resulted from growth control based on positional specification, as is common among extant organisms. Here we explore axial growth gradients in the more anterior body region, the cephalon, and in the cephalon and trunk during subsequent development in the holaspid period. We detected an axial growth gradient in the cephalon in the meraspid period, flatter and opposite in direction to that of the trunk, which also persisted during the holaspid period. We also found an holaspid trunk growth gradient, with a different distribution of growth rates among segments than that of the meraspid period. These newly observed growth gradients are compatible with the mechanism of growth control inferred for the meraspid trunk. Thus, the same kind of growth control may have operated in both body regions and during the whole ontogeny of A. koninckii. This study, along with others on the same species that preceded it, show that morphometric analysis of appropriate data sets can address questions of high interest for evolutionary developmental biology using data from fossils. By revealing developmental features at deep nodes of the phylogenetic tree, these studies will elucidate both how developmental processes evolved and how they themselves affected the evolution of organismal body patterning.近期的形态计量分析显示，在距今约4.29亿年的三叶虫奥氏沟盾壳虫（Aulacopleura koninckii）的躯干中存在幼体期（meraspid）轴向生长梯度，该梯度由基于位置特化的生长调控所介导，这一调控模式在现生生物中极为常见。本研究聚焦于更靠前的体区——头甲（cephlon）的轴向生长梯度，以及成体期（holaspid）发育过程中头甲与躯干的轴向生长梯度展开探究。我们在幼体期（meraspid）的头甲中检测到了轴向生长梯度：该梯度相较于躯干的生长梯度更为平缓，且方向与躯干生长梯度相反，且这一梯度在成体期（holaspid）仍持续存在。我们还发现了成体期（holaspid）的躯干生长梯度，其体节间生长速率的分布模式与幼体期（meraspid）存在显著差异。本次新观测到的生长梯度与基于幼体期（meraspid）躯干所推断的生长调控机制高度契合。由此可见，相同类型的生长调控可能同时作用于奥氏沟盾壳虫的两个体区，并贯穿其整个个体发育过程。本研究与此前针对该物种的同类研究共同证实，通过对合适数据集开展形态计量分析，可利用化石数据解答进化发育生物学领域的诸多关键科学问题。这类研究通过揭示系统发育树深层节点处的发育特征，既可阐明发育过程的演化路径，也能揭示发育进程本身如何影响生物体躯体构型的进化。