SeaCACHE - Seawater Chemistry And CHondrichthyan Evolution

软骨动物(鲨鱼、射线和全头类)有着极其丰富和漫长的化石记录，以牙齿和牙盘为主。这些矿化构造为该群提供了一个深部的时间、演化的视角。最近，在全头鲨的牙盘和活着的鲨鱼身体--牙齿和牙齿--中发现了一种名为白色矿化的组织，其中含有一种富含镁的生物矿物(白锁石)。这种不寻常的组织潜在地提供了一种增强功能，但在软骨动物的进化史上，白蛋白是什么时候首次出现的呢？众所周知，海水中的镁钙比(镁钙比)在地球历史上发生了变化，形成了方解石海和文石海(分别较低和较高的镁/钙比)。这些变化，以及温度，显然影响了无脊椎动物碳酸盐骨骼对特定元素和矿物质的吸收。海洋脊椎动物的骨骼也是以类似的方式塑造的吗？或者它们的骨骼矿化不受周围环境的影响？SeaCACHE项目将在这一关键的海洋动物群体中测试这些可能性。主要目的有三：(1)通过组织学和化学分析相结合的方法，分析从泥盆纪到今的各种生物的牙列以及首次发现的软骨类化石，以检验白色锁石的存在；(2)研究海水的镁/钙含量、海水温度和现代和古代生态系统中软骨类中白锁石的存在之间的关系；以及(3)更新软骨动物的系统发育，以阐明白锁石的演化速率。在这个项目中，研究人员将在化学、古环境和系统发育分析、开放科学实践、自然历史收藏管理以及其他可转让技能方面获得经验，这些技能将大大改善他们未来作为独立研究人员的职业生涯。

Chondrichthyans (sharks, rays and holocephalans) have an extremely rich and long fossil record dominated by teeth and dental plates. These mineralized structures provide a deep-time, evolutionary, perspective of the group. Recently, a hypermineralized tissue called whitlockin, containing a biomineral rich in magnesium (whitlockite), has been discovered in holocephalan dental plates and in living shark body-denticles and teeth. This unusual tissue potentially provides a strengthening function, but when did whitlockin first appear in the evolutionary history of chondrichthyans? It is known that the ratio of magnesium:calcium (Mg/Ca) in seawater has shifted through Earth history, creating intervals of 'calcite' seas and 'aragonite' seas (lower and higher Mg/Ca ratios respectively). These changes, along with temperature, apparently influenced the uptake of particular elements and minerals into the carbonate skeletons of invertebrate animals. Have marine vertebrate skeletons been shaped in a similar way? Or is their skeletal mineralization independent of the surrounding environment? The SeaCACHE project will test these possibilities in this critical group of marine animals. There are three main aims: (1) to analyze the dentitions of a broad range of living and, for the first time, fossil chondrichthyans from the Devonian to the present day, to test for the presence of whitlockin via a combination of histological and chemical analysis; (2) to examine the relationship between the Mg/Ca content of seawater, seawater temperature, and the presence of whitlockite in chondrichthyans in modern and ancient ecosystems; and (3) to update the phylogeny of chondrichthyans as a whole to elucidate rates of evolution of whitlockite. During this project, the research fellow will gain experience in chemical, palaeonvironmental and phylogenetic analyses, in open science practices, in natural history collection management, and in other transferable skills that will substantially improve their future career as an independent researcher.