Data from: Ontogenetic trajectories of septal spacing in Early Jurassic belemnites from Germany and France, and their palaeobiological implications

Based on well-preserved belemnites, the ontogenetic trajectories of septal spacing between succeeding chambers were analysed. In the examined species (Passaloteuthis laevigata, Parapassaloteuthis zieteni and Pseudohasitites longiformis) that come from Buttenheim, Germany, and Lixhausen, France, the ontogenetic trajectories of septal spacing follow exponentially increasing trends with no decreasing phase of septal crowding during the earliest ontogenetic stage. The absence of a decreasing trend at the earliest ontogenetic stage is a unique character in contrast with those in modern cuttlefish and ancient and modern nautiloids, in which the decreasing trends are related to hatching events. These ontogenetic septal spacing trends suggest that the belemnite hatchlings had only a protoconch with no chamber. These belemnite hatchlings with no chamber and therefore small embryonic shell diameter are similar to those of ammonoids. Significant difference in a statistical test that compared the protoconch size between the two localities, might suggest that there was limited transportation at the embryonic stage, although it could also just indicate differences in regional environmental conditions, age and/or degree of time averaging which might differ between the examined taxa.

本数据集基于保存完好的箭石（belemnites），对相邻壳室间的隔壁间距的个体发育轨迹展开了分析。本次研究涉及的物种包括产自德国巴滕海姆（Buttenheim）与法国利克桑（Lixhausen）的光滑突箭石（Passaloteuthis laevigata）、齐氏副突箭石（Parapassaloteuthis zieteni）以及长形假哈石（Pseudohasitites longiformis）。上述物种的隔壁间距个体发育轨迹均呈指数增长趋势，且在个体发育最早阶段未出现隔壁拥挤的递减阶段。与现代乌贼以及古今鹦鹉螺类（nautiloids）不同，本研究中最早发育阶段无递减趋势——后者的递减趋势与孵化事件密切相关。此类隔壁间距的个体发育轨迹表明，箭石幼体仅拥有胚壳（protoconch）而不具备壳室。这类无壳室且胚胎壳直径较小的箭石幼体，与菊石类的幼体特征高度相似。对两个产地的胚壳尺寸开展统计学检验后发现存在显著差异，这或许暗示胚胎阶段的搬运能力有限；但该结果也可能仅反映了不同研究类群间区域环境条件、发育年龄以及/或时间平均程度的差异。