Macroevolution and geochemistry of Cenozoic giant sharks

新生代巨鲨的宏观进化和地球化学

• 批准号: 0418042
• 负责人: Douglas Jones
• 金额: --
• 依托单位: University of Florida
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-08-15 至 2010-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0418042&HistoricalAwards=false
• 关键词: Macroevolution; geochemistry; Cenozoic; giant; sharks

ABSTRACTFossil sharks of the Family Lamnidae have a rich Cenozoic global history and are represented today by species such as the great white (Carcharodon carcharias). During the Miocene, the extinct lamnid shark C. megalodon attained truly enormous proportions. With a mean estimated body size of ~40 tons, this extinct species rivals some dinosaurs and whales as one of the largest animals that ever lived. The fundamental question that we seek to answer is .how did large body size evolve within lamnid sharks like C. megalodon?. Relative to its smaller ancestor, individuals of C. megalodon could have attained very large body size by growing faster (increased rate), for a longer time (increased longevity), or a combination of these two. These growth modes will be determined within the lamnid clade using seven extinct and modern species of Carcharodon and its sister-taxon Isurus compared to the extinct outgroup Otodus obliquus. Macroevolution is the study of evolutionary patterns and processes observed within closely related groups of species (clades). In order to understand lamnid body size macroevolution, two key features need to be determined for any given individual: (1) How many years old was it when it died? This will be done by studying chemical signatures preserved in vertebral centra; (2) How large was it? This will be determined from associated teeth, whose dimensions are highly correlated to body size. Shark skeletons are composed mostly of cartilage, which is not prone to fossilization. Nevertheless, the two elements needed for this study are exceptions to this rule: (1) vertebral centra, which during life replace cartilage with bone; and (2) durable teeth. Although incremental growth rings preserved in centra are oftentimes annular, they sometimes are not. A simple counting of the rings, therefore, could potentially lead to erroneous individual age determinations. To circumvent this problem, proxy seasonal and annual cycles represented by the oxygen isotopic signatures preserved in centra will be used to calibrate the individual age of each specimen. This will be done after centra are analyzed geochemically to determine, relative modern lamnids, the extent of diagenesis (alteration during fossilization) and how this process affected oxygen isotopic signatures archived in fossil centra. These analyses will include = determination of physical and chemical characteristics such as crystallinity, carbonate content, trace, minor, and rare earth elemental concentrations, and oxygen isotopes. Our pilot studies indicate that: (1) oxygen isotopic signatures can remain in centra even when highly altered; and (2) certain elements and compounds known to occur in unaltered bone can be used as tracers to model diagenesis in fossil bone. Intellectual Merit.--This project will integrate concepts, methods, and data from paleobiology and geochemistry. Body size macroevolution is of fundamental interest to scientists, e.g., how it might relate to the concept of Cope's "Law" (evolution of increased body size within clades). This study will provide a case study using a clade that evolved what may be the largest body size ever. The related geochemical part of this project will quantify diagenesis in bone and calibrate incremental growth in fossil sharks. These results will facilitate more informed interpretations of the isotopic signatures used forpaleobiological interpretations in other extinct vertebrates.Broader Impacts. One graduate student will use part of this project for her Ph.D. research. An undergraduate student research assistant will be recruited. This research will be presented to UF students in graduate seminars and to other colleagues/students at national meetings and invited seminars. K-12 teachers will be involved in summer research experiences. Shark teeth are highly prized by fossil collectors and inmegalodonlt evokes much public interest. This research will be disseminated to the public through general lectures, fossil festivals, field trips, newsletters, and exhibits at the Florida Museum of Natural History. The public outreach will be promoted on our website (www.flmnh.ufl.edu), which receives 7.2 million cybervisits (60 million iihitsls) per year.

摘要 鲨科鲨鱼化石具有丰富的新生代全球历史，如今以大白鲨 (Carcharodon carcharias) 等物种为代表。在中新世，已经灭绝的蜥蜴巨齿鲨达到了真正巨大的体型。 这种灭绝的物种的平均体型估计约为 40 吨，可与一些恐龙和鲸鱼媲美，成为有史以来最大的动物之一。 我们寻求回答的基本问题是，像巨齿鲨这样的蜥蜴鲨是如何进化出巨大的体型的？相对于其较小的祖先，巨齿鲨个体可以通过生长更快（增加速率）、更长的时间（延长寿命）或这两者的组合来获得非常大的体型。这些生长模式将在 lamnid 分支内使用七个已灭绝和现代的 Carcharodon 物种及其姊妹分类单元 Isurus 与已灭绝的外群 Otodus obliquus 进行比较来确定。宏观进化是对密切相关的物种群体（进化枝）中观察到的进化模式和过程的研究。 为了了解兰科动物的体型宏观进化，需要确定任何特定个体的两个关键特征：（1）它死亡时有多少岁？这将通过研究椎体中心保存的化学特征来完成； （2）它有多大？这将根据相关牙齿来确定，其尺寸与身体尺寸高度相关。鲨鱼骨骼主要由软骨组成，不易形成化石。然而，本研究所需的两个元素是该规则的例外：（1）椎体中心，在生命过程中用骨代替软骨； (2) 耐用的牙齿。虽然中心保存的增量年轮通常是环形的，但有时不是环形的。 因此，简单地计算环数可能会导致错误的个人年龄确定。为了解决这个问题，将使用中心保存的氧同位素特征代表的代理季节和年度周期来校准每个样本的个体年龄。 这将在对中心进行地球化学分析以确定相对现代的lamnids、成岩作用的程度（化石过程中的改变）以及该过程如何影响化石中心存档的氧同位素特征之后完成。这些分析将包括物理和化学特性的测定，例如结晶度、碳酸盐含量、痕量、微量和稀土元素浓度以及氧同位素。我们的初步研究表明：（1）即使高度改变，氧同位素特征也可以保留在中心； (2)已知存在于未改变的骨骼中的某些元素和化合物可以用作示踪剂来模拟骨骼化石的成岩作用。智力优势——该项目将整合古生物学和地球化学的概念、方法和数据。身体尺寸的宏观进化是科学家们的根本兴趣，例如，它如何与科普“定律”的概念（进化枝内身体尺寸增加的进化）相关。这项研究将提供一个案例研究，使用进化出可能是有史以来最大体型的进化枝。该项目的相关地球化学部分将量化骨骼的成岩作用并校准化石鲨鱼的增量生长。这些结果将有助于对用于其他灭绝脊椎动物古生物学解释的同位素特征进行更明智的解释。更广泛的影响。一名研究生将使用该项目的一部分来攻读博士学位。研究。将招聘一名本科生研究助理。这项研究将在研究生研讨会上向佛罗里达大学学生展示，并在全国会议和特邀研讨会上向其他同事/学生展示。 K-12 教师将参与暑期研究经历。鲨鱼牙齿受到化石收藏家的高度重视，巨齿鲨也引起了公众的极大兴趣。这项研究将通过一般讲座、化石节、实地考察、新闻通讯和佛罗里达自然历史博物馆的展览向公众传播。我们的网站 (www.flmnh.ufl.edu) 将促进公众宣传，该网站每年收到 720 万次网络访问 (6000 万次点击)。