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 model）以解释海洋生物对温室气候的响应。全球变暖与海平面上升可能带来两种结果：(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) 形成孤立的陆表海盆（epicontinental basin），孕育特有类群辐射演化，最终导致物种地理分布范围缩小，物种形成速率与生物多样性提升。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期-土仑期（Cenomanian–Turonian, C–T）时段，为验证上述两类端元模型提供了理想契机。具体而言，头足类（cephalopod）对这些全球环境变化的响应机制迄今尚未明确。本研究依托涵盖7262个头足类化石产出记录的全球数据库，分析了C–T时段内的生物多样性变化。物种级与属级生物多样性均在晚森诺曼期达到峰值。C–T界线处的全球生物多样性降幅较为平缓；相较而言，生物多样性在中森诺曼期与中土仑期——两段短暂降温的时期——处于较低水平。不同区域的多样性响应差异，或可反映不同海洋环境背景下环境扰动的程度与发生时序。令人意外的是，欧洲陆架、北美西部内陆与南大西洋海域的头足类动物群均在C–T界线处向赤道方向迁移，而其余区域的头足类纬度分布未发生显著变化。整个C–T时段内，属级单元的全球地理分布范围未发生明显变化，但C–T界线处广布属（cosmopolitan genus）的占比在全球尺度及欧洲、北美西部内陆区域均出现显著提升，而太平洋与南大西洋海域的广布类群占比却有所下降。针对温室环境下生物多样性变化的两类端元模型，均无法解释C–T时段头足类的多样性变化特征——其生物多样性提升并未伴随地理分布范围的扩张。这或许意味着，海平面上升与全球变暖既推动了陆表海盆中的特有类群辐射演化，也使得部分区域的广布类群数量增加，这也凸显了结合全球与区域尺度分析的重要性。