Data from: Marine life in a greenhouse world: cephalopod biodiversity and biogeography during the early Late Cretaceous

Two end-member models are proposed to explain marine biotic responses to greenhouse conditions. Global warming and increasing sea level may: (1) promote dispersal of marine species, leading to larger geographic ranges and decreased speciation and biodiversity, or (2) form isolated epicontinental basins that host endemic radiations, leading to smaller geographic ranges and increased speciation and biodiversity. The Cenomanian–Turonian (C–T) interval, marked by greenhouse warming, sea level rise, ocean anoxia, and biotic turnover, presents an opportunity to test these two end-member models. In particular, how cephalopods responded to these global changes has not been clear. A global database of 7,262 cephalopod occurrences was used to evaluate biodiversity changes through the C–T interval. Both species- and genus-level diversity peaked in the Late Cenomanian. The global diversity drop across the C/T boundary was modest; rather, diversity was low during the Middle Cenomanian and Middle Turonian, times of brief cooling. Regional variations in diversity responses may reflect the degree and timing of environmental perturbations within different oceanographic settings. Surprisingly, cephalopod faunas in the European Platform, Western Interior, and South Atlantic all shifted equatorward across the C/T boundary, whereas other regions saw no change in latitudinal distributions. Global generic geographic ranges did not change through the C–T interval, but the percentage of cosmopolitan genera did increase significantly across the C/T, both globally and within the Western Interior and Europe, whereas cosmopolitans dropped in the Pacific and South Atlantic. Neither end-member model for biodiversity change in a greenhouse world is supported for C–T cephalopods, as diversity increased without an associated increase in geographic range. It may be that sea level rise and global warming led to both endemic radiations in epicontinental basins and an increase in cosmopolitan taxa in some regions, demonstrating the importance of combining global and regional scale analyses.

本研究提出两类端元模型（end-member models），用以阐释海洋生物对温室气候状态的响应。全球变暖与海平面上升可能引发两种演化结果：(1) 促进海洋物种扩散，使其地理分布范围扩大，同时降低物种形成速率与生物多样性；或(2) 形成相互隔离的陆表海盆地（epicontinental basins），孕育特有类群辐射演化，最终导致物种地理分布范围缩小，提升物种形成速率与生物多样性。以温室变暖、海平面上升、海洋缺氧及生物更替为标志性特征的森诺曼阶-土仑阶（Cenomanian–Turonian, C-T）时段，为检验这两类端元模型提供了绝佳研究契机。目前学界对头足类（cephalopods）如何响应此类全球环境变化的机制仍不明晰。本研究依托涵盖7262条头足类化石出现记录的全球数据库，评估了C-T时段的生物多样性变化。研究显示，物种级与属级多样性均在晚森诺曼期达到峰值；C-T界线处的全球多样性下降幅度较为平缓，而生物多样性低谷出现在存在短暂降温事件的中森诺曼期与中土仑期。多样性响应的区域差异，或反映了不同海洋环境背景下环境扰动的程度与时间节点存在区别。令人意外的是，欧洲陆表台地、北美西部内陆及南大西洋的头足类动物群在C-T界线处均向赤道方向迁移，而其他区域的头足类纬度分布格局未发生显著变化。全球属级地理分布范围在C-T时段内未出现明显改变，但广布属（cosmopolitan genera）的占比在全球尺度及北美西部内陆、欧洲区域均显著上升，而太平洋与南大西洋的广布属占比则出现下降。两类针对温室世界生物多样性变化的端元模型，均无法解释C-T时段头足类的多样性变化模式——该时段生物多样性上升并未伴随地理分布范围的同步扩张。这或许意味着，海平面上升与全球变暖可同时驱动陆表海盆地的特有类群辐射演化，以及部分区域广布类群丰度的提升，凸显了结合全球与区域尺度开展分析的重要性。