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Using tooth wear to impose ecological constraints on isotopic and biostratigraphic analyses based on conodonts

利用牙齿磨损对基于牙形刺的同位素和生物地层分析施加生态约束

基本信息

批准号：
NE/F010982/1
负责人：
Mark Purnell
金额：
$ 7.14万
依托单位：
University of Leicester
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2008
资助国家：
英国
起止时间：
2008 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FF010982%2F1
关键词：
Using tooth wear impose ecological

项目摘要

This study will test the hypothesis that wear patterns on fossil conodont teeth differ according to whether species lived on the sea floor or above it. If wear does differ, as it does in fish teeth, this will provide a new way of increasing the reliability of conodonts in geological and deep-time environmental analysis. Conodonts were small, eel-like primitive fishes. They have been extinct since the end of the Triassic, but the 300 million year record of their microscopic fossil teeth is exceptionally complete, and they are easy to obtain in large numbers by dissolving limestone in weak acid. Consequently, conodonts are among the most important tools for geological dating - determining when rocks were laid down and when geological events occurred. They are also increasingly important tools for investigating the palaeoclimate, palaeotemperature and palaeooceanography of geological periods in deep time, studies which are important for understanding the context of current climate change. For example, investigations of the oxygen isotopes in conodont teeth are providing new insights into glaciations, sea level and sea temperature hundreds of millions of years ago. Conodonts are particularly suited to such studies because the structure and calcium phosphate composition of their tooth crown maximises the chances that the chemical signatures recorded in the teeth reflect ocean conditions at the time the animal was alive, and minimises changes caused by the process of fossilization. Recent work indicates that isotopic analyses based on conodont crown tissue give more reliable results than analyses of any other fossil teeth or shells of comparable age. Realising the full potential of conodonts, however, requires that we can constrain their ecology and mode of life. Differentiating between benthic taxa, which lived on the sea floor, and pelagic taxa, which lived away from the sea floor and in surface waters, is particularly important. The best taxa for geological dating are pelagic, because pelagic taxa have broader (potentially global) distributions. They also disperse more rapidly, so the time at which a newly evolved pelagic species first appears in the fossil record in different locations is more likely to be synchronous (important for establishing the age equivalence of rock sequences). Analyses that interpret shifts in the chemical composition of conodont tooth crowns in terms of temperature or sea level must exclude the possibility that differences between samples reflect differences in the depth habitat at which the sampled conodont species lived (deeper water is cooler). Unfortunately, the mode of life of conodonts is poorly constrained, and this causes problems. We know that they were active swimming animals that ranged from shallow nearshore through to deep ocean environments, but determining whether a particular species occupied a benthic or a pelagic niche is difficult. Current methods, based on hypothetical distributions of conodonts along depth gradients, are rather crude and generally unreliable. This proposal aims to develop a new approach to constraining the depth habitats of conodont taxa. Recent work led by the investigator discovered that patterns of tooth wear in benthic feeding fish differ from those of pelagic feeding fish and can be used to study changes in feeding in fossil fish. Does the same apply to conodonts? In order to find out we will conduct the first systematic analysis of conodont tooth wear and test the hypothesis that pelagic feeding and benthic feeding species exhibit different wear patterns. This will be based on microscopic investigation of hundreds of conodont teeth and detailed statistical analysis of the patterns of wear preserved on their surfaces. These teeth will be taken from samples where, unlike most conodonts, the palaeoecology of the species is well constrained. If differences are detected, isotopic analysis will provide independent data concerning temperature/depth habitat.

这项研究将检验这样一种假设，即牙形刺化石牙齿的磨损模式因物种生活在海底还是海底而有所不同。如果磨损确实不同，就像在鱼牙上的情况一样，这将提供一种新的方法，在地质和深层环境分析中增加牙形刺的可靠性。牙形刺是一种小型的、类似鳗鱼的原始鱼类。自三叠纪结束以来，它们已经灭绝，但对它们微观化石牙齿的3亿年记录异常完整，通过在弱酸中溶解石灰岩很容易获得大量它们。因此，牙形刺是地质测年的最重要工具之一--确定岩石何时铺设和地质事件何时发生。它们也是研究深部地质时期的古气候、古温度和古海洋学的日益重要的工具，这些研究对于理解当前气候变化的背景很重要。例如，对牙形刺牙齿中氧同位素的研究为了解数亿年前的冰川、海平面和海温提供了新的见解。牙形刺特别适合于这类研究，因为它们牙冠的结构和钙磷酸盐成分最大限度地增加了牙齿中记录的化学特征反映动物活着时的海洋条件的机会，并将石化过程造成的变化降至最低。最近的工作表明，基于牙形刺牙冠组织的同位素分析比对任何其他类似年龄的牙齿或贝壳化石的分析得出的结果更可靠。然而，要实现牙形刺的全部潜力，需要我们能够限制它们的生态和生活模式。区分生活在海底的底栖类群和生活在远离海底和表层水域的远洋类群尤为重要。最适合地质年代测定的类群是远洋类群，因为远洋类群的分布范围更广(可能是全球性的)。它们的扩散速度也更快，因此新进化的远洋物种首次出现在不同地点的化石记录中的时间更有可能是同步的(这对于确定岩石序列的年龄等价性很重要)。用温度或海平面来解释牙形刺牙冠的化学成分变化的分析必须排除这样一种可能性，即样本之间的差异反映了样本牙形刺物种所生活的深度栖息地的差异(水越深越冷)。不幸的是，牙形刺的生活方式受到很少的限制，这就造成了问题。我们知道它们是活跃的游泳动物，从浅海近岸到深海环境，但很难确定某个特定物种是占据海底生态位还是远洋生态位。目前的方法基于牙形刺沿深度梯度的假设分布，相当粗糙，通常不可靠。这项提议旨在开发一种新的方法来限制牙形刺分类群的深度栖息地。这位研究人员最近领导的工作发现，底栖摄食性鱼类的牙齿磨损模式与远洋摄食性鱼类的不同，可以用来研究化石鱼类摄食的变化。同样的道理也适用于牙形刺吗？为了找出答案，我们将首次对牙形刺牙齿磨损进行系统分析，并检验远洋摄食和底栖摄食物种表现出不同磨损模式的假说。这将基于对数百颗牙形牙齿的微观调查和对其表面保存的磨损模式的详细统计分析。这些牙齿将从样本中提取，与大多数牙形刺不同，该物种的古生态受到很好的限制。如果检测到差异，同位素分析将提供关于温度/栖息地深度的独立数据。