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.

Lamnidae家族的AbstractFossil鲨鱼具有丰富的新生代历史，如今由大白（Carcharodon Carcharias）等物种代表。在中新世期间，灭绝的Lamnid鲨鱼C. Megalodon真正获得了巨大的比例。 这种灭绝的物种的平均估计体大小约为40吨，与有史以来最大的动物之一相媲美的恐龙和鲸鱼。 我们寻求回答的基本问题是。大体尺寸在C. Megalodon之类的Lamnid鲨鱼中如何发展？相对于其较小的祖先，C。Megalodon的个体可以通过更快的速度（增加速率），更长的时间（增加寿命）或组合这两者来达到非常大的体型。这些生长模式将在lamnid进化枝内使用七种灭绝和现代物种与灭绝的外otodus斜斜肌相比，及其姊妹二叶氏菌及其姊妹及其伊苏鲁斯。宏观进化是对密切相关的物种（进化枝）中观察到的进化模式和过程的研究。 为了理解lamnid体型宏观进化，需要确定任何给定个体的两个关键特征：（1）死亡时有多少年？这将通过研究椎Centra保存的化学特征来完成。 （2）它有多大？这将由相关的牙齿确定，其尺寸高度相关与体型。鲨鱼骨骼主要由软骨组成，不容易被化石。然而，这项研究所需的两个要素是该规则的例外：（1）椎骨中心，在生命中，用骨头代替软骨； （2）耐用的牙齿。尽管在Centra中保留的增量生长环通常是环形的，但有时不是。 因此，对环的简单计数可能会导致错误的个人年龄确定。为了解决这个问题，由Centra保存的氧同位素特征代表的替代季节性和年度周期将用于校准每个标本的个体年龄。 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（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后完成此操作。这些分析将包括=确定物理和化学特征，例如结晶度，碳酸盐含量，痕量，小地球元素浓度以及氧同位素。我们的试点研究表明：（1）即使高度改变，也可以保留在Centra中氧气； （2）某些已知发生在不变骨骼中的元素和化合物可以用作模拟化石骨成岩作用的示踪剂。智力优点 - 这个项目将整合古生物学和地球化学的概念，方法和数据。体型宏观进化具有科学家的基本兴趣，例如，它与Cope的“定律”概念（进化枝内增加的体型的演变）可能如何相关。这项研究将使用进化枝来提供案例研究，该进化枝进化出可能是有史以来最大的体型。该项目的相关地球化学部分将量化骨骼中的成岩作用，并校准化石鲨鱼的增量生长。这些结果将促进对其他灭绝脊椎动物中使用遗传学解释的同位素特征的更明智的解释。一名研究生将使用该项目的一部分作为博士学位。研究。将招募本科生研究助理。这项研究将在全国会议和邀请研讨会上向UF学生和其他同事/学生提交给UF学生。 K-12教师将参与夏季研究经验。鲨鱼的牙齿受到化石收集器的高度珍视，而Inmegalodonlt引起了人们的极大兴趣。这项研究将通过一般讲座，化石节，实地考察，新闻通讯和展览会在佛罗里达自然历史博物馆中传播给公众。公众推广将在我们的网站（www.flmnh.ufl.edu）上促进，该网站每年将获得720万个网络视网膜（6000万IIHITSL）。