SeaCACHE - Seawater Chemistry And CHondrichthyan Evolution

软骨鱼类（鲨鱼、鳐鱼和全头类）有着极其丰富和悠久的化石记录，主要是牙齿和牙板。这些矿化结构提供了一个深时间，进化，该集团的观点。最近，在全头类动物的齿板和活鲨鱼的体齿和牙齿中发现了一种叫做白洛克金的高矿化组织，含有富含镁的生物矿物（白洛克石）。这种不寻常的组织可能提供了一种强化功能，但惠特洛克金是什么时候首次出现在软骨鱼类的进化史上的呢？众所周知，海水中的镁钙比（Mg/Ca）在地球历史上发生了变化，形成了“方解石”海和“文石”海（分别为较低和较高的Mg/Ca比）。这些变化，沿着温度的变化，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形成的吗？或者它们的骨骼矿化与周围环境无关？SeaCACHE项目将在这一关键的海洋动物群体中测试这些可能性。有三个主要目标：（1）分析从泥盆纪至今的各种活的软骨鱼类的齿系，并首次分析化石软骨鱼类，通过组织学和化学分析相结合的方法来检验whitlockin的存在;（2）检验海水中Mg/Ca含量、海水温度与现代和古代生态系统中软骨鱼类中whitlockin的存在之间的关系;（3）更新了软骨鱼类的整体演化史，阐明了白洛克石的演化速率。在这个项目中，研究员将获得化学，古生物学和系统发育分析，开放科学实践，自然历史收藏管理以及其他可转移技能的经验，这些技能将大大提高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.