Fish like it hot? Response of fish and shark communities to abrupt past global warming

古新世-始新世极热期（PETM）约5600万年前，是一系列新生代全球变暖突变事件中最大的一次。在这一事件中，海洋迅速变暖了50摄氏度，变得更酸，世界变得更潮湿，风暴更多，对陆地和海洋上的生命产生了深远的影响。PETM是由同位素轻碳（可能来自火山活动）注入大气驱动的，许多相关的环境变化与今天发生的环境变化相似。因此，PETM常被认为是理解人为环境变化及其影响的最佳地质模拟。然而，尽管有大量的研究调查了始新世新时期生物和环境的变化，但很少有研究调查其对海洋脊椎动物的反应和长期影响。至少在某种程度上，这是因为人体化石记录是不完整的，因为缺乏合适的沉积物，而且对可用序列的年龄控制非常差，无法评估短期生物反应。然而，解决顶级营养消费者对现代人为变化的反应和恢复能力至关重要，因为预测未来一个世纪热带群落的生产力、多样性和体型将显著减少，这将对许多海洋生态系统和依赖这些资源的人口产生重大影响。幸运的是，鱼石（=鱼牙和鲨鱼牙，通常小于1毫米）在海洋沉积物中普遍存在，是一种未被充分利用但功能强大的资源，可以产生相对连续的、高度时间和空间分解的鱼类和鲨鱼群落记录。该学生将利用这一新颖的档案来汇编现有记录，并生成多个关于全球PETM鱼类和鲨鱼群落生产力和多样性变化的新记录。这些数据将与广泛的古环境数据集相结合。将解决的关键问题包括：-鲨鱼和鱼类群落如何在PETM中发生变化？高纬度社区和低纬度社区的反应相似吗？-温度是鱼类和鲨鱼群落变化的主要驱动力吗？-气候突变事件对鱼类和鲨鱼进化的影响是什么？

The Palaeocene-Eocene Thermal Maximum (PETM) ~56 million years ago, is the largest of a series of abrupt Cenozoic global warming events. During this event, the oceans rapidly warmed by >5 degrees C and became more acidic, and the world became wetter and stormier with profound consequences for life on land and in the oceans. The PETM was driven by the injection of isotopically light carbon (likely from volcanism) into the atmosphere, and many of the associated environmental changes are similar to those occurring today. Therefore, the PETM is often considered the best geological analogue to understand anthropogenic environmental change and its impacts. However, whilst a large number of studies have investigated PETM biotic and environmental change, very few have investigated the response and long-term impact on marine vertebrates. This is, at least in part, because the body fossil record is patchy, because of a lack of suitable sediments and very poor age control on available sequences to assess short-term biological responses. Yet, resolving the response and resilience of top level trophic consumers to modern anthropogenic change is of vital importance because of predictions of significant reductions in tropical communities productivity, diversity and body size over the coming century with critical implications for many marine-ecosystems and human populations dependent on these resources. Fortunately, ichthyoliths (= fish teeth and shark denticles, generally <1 mm in size) are pervasive in marine sediments and are an underutilized but powerful resource for generating relatively continuous and highly temporally and spatially resolved records of fish and shark communities through time. The student will utilise this novel archive to compile existing records and generate multiple new records of changes in the productivity and diversity of fish and shark communities across the PETM globally. These data will be integrated with extensive palaeoenvironmental datasets. Key questions that will be addressed include: - How did shark and fish communities change across the PETM? - Did high vs low latitude communities respond similarly?- Was temperature the dominant driver of change in fish and shark communities?- What role do abrupt climate events play in shaping fish and shark evolution?