Fossil Mammals, Carbon Isotopes, and Evolution of Cenozoic Terrestrial Ecosystems in Argentina

麦克法登9506550 该提案寻求NSF对一个为期三年的项目的资助，该项目利用阿根廷经典的60万年序列调查南美洲南部新生代哺乳动物食草动物群落的古老摄食生态和进化。 该研究将解决哺乳动物化石古生态学的三个相互关联的主题：（1）为什么灭绝的无蹄动物在南美洲比大多数北方半球高冠食草哺乳动物更早获得高冠牙齿和可能的放牧饮食的长期谜团;（2）地方性/移民哺乳动物摄食生态学，旨在更好地了解上新世-更新世大美洲交流期间的生物相互作用;（3）C_3和C_4光合作用的演化与南美南部草地扩展的时间。 本研究将通过（1）测定稳定碳同位素 （13 C）牙釉质的值和（2）分析臼齿形态（即，相对未磨损树冠高度）。 碳同位素的数据结合齿冠高度将确定一个特定的灭绝草食动物类群是C3浏览器，C3食草动物，混合饲养者，还是C4食草动物。 （在新生代中晚期，纯C3饲养者的牙釉质磷灰石平均值为13，-13份/密耳，而前C4-饲养者的平均牙釉质磷灰石值为约1.5份/密耳。百分之零。 一般来说，低冠食草哺乳动物主要是浏览器，而高冠食草哺乳动物主要是食草动物。 这两种方法，直到最近才被一起使用，是化石哺乳动物古生物学中一个强大的新工具，可以理解长期的生态系统演化和地质时期的全球变化。 请拨经费用于：（1）前往犹他州的拉普拉塔（1次）、美国自然历史博物馆（1次）和菲尔德自然历史博物馆（1次），为同位素分析获取更多标本和建立哺乳动物食草动物高齿类数据库的博物馆旅费;（3）我的阿根廷同事（普拉多）参观佛罗里达自然历史博物馆的一次旅费;（4）研究生助教奖学金一项。

MacFadden 9506550 This proposal seeks NSF grant support for a three-year project to investigate the ancient feeding ecology and evolution of Cenozoic mammalian herbivore communities of southern South America using the classic 60-myr sequence from Argentina. The research will address three interrelated themes of fossil mammal paleoecology: (1) the long-standing enigma of why extinct notoungulates acquired high-crowned teeth, and presumably grazing diets, earlier in South America than most northern hemisphere high-crowned herbivorous mammals; (2) endemic/immigrant mammal feeding ecology with the goal of a better understanding of biotic interactions during the Plio-Pleistocene Great American Interchange; and (3) the evolution of C3 an C4 photosynthesis and timing of grassland spread in southern South America. This study will be accomplished by (1) determining the stable carbon isotope ( 13C) values of tooth enamel and (2) analyzing molar tooth morphology (i.e., relative unworn crown height). The data from carbon isotopes combined with tooth-crown height will determine whether a particular extinct herbivore taxon was a C3 browser, C3 grazer, mixed feeder, or C4 grazer. (During the middle and late Cenozoic, pure C3 feeders have mean tooth enamel apatite 13 values of ca. -13 parts per mil, whereas pre C4-feeders have mean tooth enamel apatite values of ca. 0%. In general, low-crowned herbivorous mammals are predominately browsers, whereas high-crowned herbivorous mammals are predominately grazers. These two methods, which until recently have not been used together, are a powerful new tool in fossil mammal paleontology to understand long-term ecosystem evolution and global change through geologic time. Funds are requested for (1) museum travel to obtain additional specimens for isotopic analysis and to construct a data base on mammalian herbivore hypsodonty at La Plata (1 trip), the American Museum of Natural History (1 trip), and the Field Museum of Natural History (1 trip); of Utah; (3) one trip for my Argentine colleague (Prado) to visit the Florida Museum of Natural History; and (4) one graduate student assistantship.