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（morphometric analysis）显示，在距今约4.29亿年的三叶虫（trilobite）奥勒克三叶虫（Aulacopleura koninckii）的躯干中，存在幼体分节期（meraspid）的轴向生长梯度（axial growth gradient）；该生长梯度由基于位置特化（positional specification）的生长调控所形成，这一调控方式在现生生物（extant organisms）中普遍存在。本研究旨在探究更靠前的躯体区域——头甲（cephalon），以及成体期（holaspid period）内头甲与躯干在后续发育过程中的轴向生长梯度。我们在分节期的头甲中检测到轴向生长梯度：该梯度较躯干的生长梯度更为平缓，且方向相反，且这一梯度在成体期同样持续存在。此外，我们还发现成体期躯干存在生长梯度，其体节（segments）间的生长速率分布模式与分节期存在差异。本次新观测到的这些生长梯度，与我们基于分节期躯干推断出的生长调控机制相契合。由此可见，奥勒克三叶虫的躯体两个区域以及整个个体发育（ontogeny）过程中，或许采用了同一类生长调控机制。本研究与此前针对该物种的同类研究共同证实：借助合适的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（evolutionary developmental biology）领域的诸多关键科学问题。此类研究通过揭示系统发育树（phylogenetic tree）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模式建成（body patterning）的演化。