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

该项目旨在利用阿根廷的经典60-myr序列，研究南美洲南部新生代食草哺乳动物群落的古代喂养生态和进化。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)长期存在的谜题：为什么灭绝的无齿动物在南美洲比大多数北半球的高冠食草哺乳动物更早获得高冠牙齿和可能的食草饮食；(2)以更好地理解上新世-更新世大美洲大交换时期生物相互作用为目标的地方性/移民哺乳动物摄食生态学；(3)南美南部C3和C4光合作用的演化与草地扩张的时代。本研究将通过(1)测定牙釉质的稳定碳同位素（13C）值和(2)分析臼齿形态（即相对未磨损的冠高度）来完成。碳同位素数据结合齿冠高度将确定一个特定的灭绝食草动物分类群是C3食草动物、C3食草动物、混合食草动物还是C4食草动物。(在新生代中晚期，纯C3喂养体的牙釉质磷灰石平均值约为0.13 - 0.13，而前c4喂养体的牙釉质磷灰石平均值约为0.0%。一般来说，低冠草食性哺乳动物主要是食草动物，而高冠草食性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，是哺乳动物化石古生物学中一种强大的新工具，可以通过地质时间来理解长期的生态系统进化和全球变化。(1)在拉普拉塔（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）进行博物馆旅行，以获得更多的标本进行同位素分析，并建立哺乳动物食草动物假说的数据库；犹他州;(3)我的阿根廷同事（普拉多）去参观佛罗里达自然历史博物馆；(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.