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.

摘要鲨科的鲨鱼化石具有丰富的新生代全球历史，今天的代表物种是大白色（Carcharodon carpidas）。在中新世，灭绝的板鲨C。巨齿鲨达到了真正巨大的比例。 这种灭绝的物种的平均估计身体大小约为40吨，与一些恐龙和鲸鱼竞争，成为有史以来最大的动物之一。 我们试图回答的基本问题是：像C。巨齿鲨？相对于其较小的祖先，C.巨齿鲨可以通过更快的生长速度（增加速率）、更长的时间（增加寿命）或两者的结合来获得非常大的体型。这些增长模式将被确定在lamnid分支使用Carcharodon和它的姐妹分类群Isurus的7个灭绝和现代物种相比，灭绝的外类群Otodus的。宏观进化是研究在密切相关的物种群体（分支）中观察到的进化模式和过程。 为了了解lamnid身体大小的宏观进化，需要确定任何给定个体的两个关键特征：（1）它死亡时的年龄是多少？这将通过研究保存在椎体中心的化学特征来完成;（2）它有多大？这将由相关的牙齿确定，其尺寸与身体大小高度相关。鲨鱼的骨骼主要由软骨组成，不易软骨化。然而，这项研究所需的两个元素是这一规则的例外：（1）椎体，在生命过程中用骨骼代替软骨;（2）耐用的牙齿。虽然生长轮保存在centra通常是环形的，他们有时不是。 因此，简单的年轮计数可能会导致错误的个体年龄测定。为了避免这个问题，代理季节和年度周期代表保存在centra的氧同位素签名将被用来校准每个标本的个人年龄。 这将在对centra进行地球化学分析以确定相对现代的lamnids，成岩作用的程度（石化过程中的蚀变）以及该过程如何影响化石centra中存档的氧同位素特征之后进行。这些分析将包括=确定物理和化学特性，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）即使在高度改变的情况下，氧同位素特征也可以保留在centra中;（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化石骨骼中的成岩作用。智力价值。该项目将整合古生物学和地球化学的概念、方法和数据。身体大小的宏观进化是科学家的根本兴趣，例如，它如何与科普的“法则”（进化分支内身体尺寸增加的进化）的概念有关。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的身体尺寸的分支。该项目的相关地球化学部分将量化骨骼中的成岩作用，并校准鲨鱼化石的增量。这些结果将有助于对用于其他已灭绝脊椎动物古生物学解释的同位素特征进行更有根据的解释。一个研究生将使用这个项目的一部分为她的博士学位。research.将招聘一名本科生研究助理。这项研究将提交给UF学生在研究生研讨会和其他同事/学生在全国会议和邀请研讨会。K-12教师将参与夏季研究经验。鲨鱼牙齿受到化石收藏家的高度重视，巨齿鲨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、通讯和佛罗里达自然历史博物馆的展览向公众传播。将在我们的网站（www.flmnh.ufl.edu）上宣传公共外联活动，该网站每年的网络访问量为720万次（6 000万次iihitsls）。