Supplementary Tables from Mechanisms and drivers of belemnite body-size dynamics across the Pliensbachian–Toarcian crisis

Body-size reduction is considered an important response to current climate warming and has been observed during past biotic crises, including the Pliensbachian–Toarcian crisis, a second-order mass extinction. However, in fossil cephalopod studies, the mechanisms and their potential link with climate are rarely investigated and palaeobiological scales of organization are not usually differentiated. Here, we hypothesize that belemnites reduce their adult size across the Pliensbachian–Toarcian boundary warming event. Belemnite body-size dynamics across the Pliensbachian–Toarcian boundary in the Peniche section (Lusitanian Basin, Portugal) were analysed based on the newly collected field data. We disentangle the mechanisms and the environmental drivers of the size fluctuations observed from the individual to the assemblage scale. Despite the lack of a major taxonomic turnover, a 40% decrease in rostrum volume is observed across the Pliensbachian–Toarcian boundary, before the Toarcian Oceanic Anoxic Event where belemnites go locally extinct. The pattern is mainly driven by a reduction in adult size of the two dominant species, <i>Pseudohastites longiformis</i> and <i>Passaloteuthis bisulcata.</i> Belemnite-size distribution is best correlated with fluctuations in a palaeotemperature proxy (stable oxygen isotopes); however, potential indirect effects of volcanism and carbon cycle perturbations may also play a role. This highlights the complex interplay between environmental stressors (warming, deoxygenation, nutrient input) and biotic variables (productivity, competition, migration) associated with these hyperthermal events in driving belemnite body size.

体型缩小被视作应对当代气候变暖的重要策略之一，该现象在以往诸多生物危机事件中均有观测记录，其中包括二级生物集群灭绝事件——普林斯巴阶-托阿尔阶危机。然而，在化石头足类相关研究中，体型缩小的内在机制及其与气候的潜在关联极少得到探讨，且古生物学组织尺度的划分通常未被纳入考量。本研究提出假说：箭石类在普林斯巴阶-托阿尔阶界线的变暖事件中发生了成年个体体型缩小现象。基于新采集的野外实测数据，我们对葡萄牙卢西塔尼安盆地佩尼切剖面中横跨普林斯巴阶-托阿尔阶界线的箭石体型动态开展了系统分析。我们从个体到组合尺度，对观测到的体型波动的内在机制与环境驱动因子进行了解构与解析。尽管未出现显著的类群更替现象，但在托阿尔阶海洋缺氧事件（箭石在此区域发生局部灭绝）发生前的普林斯巴阶-托阿尔阶界线处，箭石鞘体体积出现了40%的降幅。该体型变化格局主要由两个优势物种——长形假壮箭石（Pseudohastites longiformis）与双沟箭石（Passaloteuthis bisulcata）的成年个体体型缩小所驱动。箭石体型分布与古温度代用指标（稳定氧同位素）的波动呈现最高相关性，但火山活动与碳循环扰动带来的潜在间接效应也可能参与了体型调控。本研究凸显了与这类超热事件相关的环境胁迫因子（气候变暖、水体缺氧、营养输入）与生物变量（生产力、种间竞争、物种迁移）之间的复杂相互作用，而这些因子共同调控了箭石的体型变化。