Reductions in body size of benthic macroinvertebrates as a precursor of the Early Toarcian (Early Jurassic) extinction event in the Lusitanian Basin, Portugal

Reduction of body size is a common response of organisms to environmental stress. Studying the Early Toarcian succession in the Lusitanian Basin of Portugal, we tested whether the shell size of benthic marine communities of bivalves and brachiopods changed at and prior to the global, warming-related Toarcian Oceanic Anoxic Event (T-OAE). Statistical analyses of shell size over time show that the mean shell size of communities decreased significantly prior to the T-OAE. This trend is distinct in brachiopods and is caused by larger-sized species becoming less abundant over time, whereas it is not significant in bivalves, suggesting a decoupled response to environmental stress. Reductions in shell size precede the decline in standardized sample-level species richness associated with the Early Toarcian extinction event. Such decreases in the shell size of marine invertebrates, well before the onset of biodiversity change, suggest that reductions in body size more generally may be a precurso...

体型缩减是生物体应对环境胁迫的普遍响应方式。本研究以葡萄牙卢西塔尼亚盆地（Lusitanian Basin）的早托阿尔阶（Early Toarcian）地层序列为研究对象，旨在探究由双壳类（bivalves）与腕足类（brachiopods）组成的底栖海洋群落（benthic marine communities）的壳体尺寸，在全球变暖相关的托阿尔阶海洋缺氧事件（Toarcian Oceanic Anoxic Event, T-OAE）发生期间及之前是否发生变化。通过对壳体尺寸随时间变化的统计分析，研究发现群落平均壳体尺寸在T-OAE发生前已出现显著减小。该缩减趋势在腕足类中尤为显著，其成因在于大型物种的丰度随时间逐渐降低；而双壳类未呈现显著的尺寸变化趋势，这表明不同类群对环境胁迫的响应存在解耦现象。壳体尺寸缩减的发生时间早于与早托阿尔阶灭绝事件相关的标准化样品物种丰富度下降过程。这类在生物多样性变化启动前就出现的海洋无脊椎动物壳体尺寸缩减现象，暗示体型缩减或许是更为普遍的环境胁迫响应前兆...