Trophic Diversity in the Santa Cruz Formation Herbivore Guild

凯斯西保护区圣克鲁斯组食草动物GuildDarin Croft的营养多样性阿根廷的圣克鲁斯组(距今16-1750万年，中新世早期)产生了一系列保存完好的壮观化石，非常适合研究灭绝哺乳动物的生物学。我们的项目将使用这些标本为两个最多样化和最丰富的圣克鲁斯哺乳动物群体制作第一个详细的饮食重建：海豚形啮齿类动物(包括豚鼠、龙舌兰、水豚、豪猪和它们已灭绝的亲属)和地方性有蹄类动物(各种已灭绝的有蹄哺乳动物群体，仅生活在南美洲，没有留下活着的后代)。由于许多圣克鲁斯物种是灭绝家族中最著名的化石代表，这些饮食数据对任何研究以植物为食的哺乳动物的进化或古代南美哺乳动物群落生态的人都是有价值的。在这些群体中，几乎所有以前的饮食研究都依赖于相对牙冠高度，这是一个与现存哺乳动物的饮食和行为生态(例如，摄食高度)相关的变量，但在许多灭绝的群体中，其相关性尚不清楚(特别是那些牙齿不断增长的群体，如Notounulates，一种非常多样化的灭绝有蹄哺乳动物群体)。在初步调查的基础上，我们将使用两种替代的饮食重建方法：低倍釉质微磨损(检查牙齿S表面的小凹坑和划痕)和中耳(评估宏观磨损和牙尖形状)。通过收集基本上不依赖于过度饮食的数据，这项研究将测试过度饮食在推断已灭绝的南美哺乳动物以及其他已灭绝群体的饮食方面的可靠性。我们的研究将是第一次对许多正在考虑的灭绝家庭的饮食进行直接分析，并将包括第一次对活着的海绵体啮齿动物进行微穿戴的调查。我们还将研究活的海绵体啮齿动物门牙形态与饮食的关系，以测试门牙形态是否能为灭绝啮齿动物的饮食提供线索。其他研究已经将门牙形态的各个方面与其他啮齿类动物的饮食相关联，但还没有一项研究检查这一特定群体中与饮食相关的变异。鱼腥草很不像？典型的？大鼠和小鼠，并被假设填补了兔子和其他大陆上各种有蹄哺乳动物所扮演的生态角色。我们项目的成果将被纳入克利夫兰自然历史博物馆的展品中，并将在凯斯西储大学的一门新的哺乳动物多样性和进化课程中得到强调。该项目将促进两名年轻研究人员的职业生涯，并将通过为期一天的以博物馆为基础的克利夫兰地区公立高中教师培训计划，增加未被充分代表的群体在科学进程中的参与；该培训计划将利用我们对南美哺乳动物的研究，为10年级学生创建教授古生物学研究基础的教案。我们将通过在科学期刊上发表文章、在大学和博物馆的公开讲座以及在科学会议上发表演讲，以及通过创新的互联网资源，如新的微型服装和中耳图像的公共互联网档案馆，来广泛传播这项研究的成果。

Trophic Diversity in the Santa Cruz Formation Herbivore GuildDarin Croft, Case Western Reserve The Santa Cruz Formation of Argentina (16-17.5 million years old; early Miocene Epoch) has produced a spectacular array of well-preserved fossils that are highly suitable for studying the biology of extinct mammals. Our project will use these specimens to produce the first detailed dietary reconstructions for two of the most diverse and abundant groups of Santa Cruz mammals: caviomorph rodents (the group that includes guinea pigs, chinchillas, capybaras, porcupines, and their extinct relatives) and endemic ungulates (various extinct groups of hoofed mammals that lived exclusively in South America and that left no living descendants). Because many Santa Cruz species are the best known fossil representatives of extinct families, these dietary data will be valuable for anyone investigating the evolution of plant-eating mammals or the ecology of ancient South American mammal communities. Nearly all prior dietary studies in these groups have relied on relative tooth crown height (hypsodonty), a variable correlated with diet and behavioral ecology (e.g., feeding height) in extant mammals but whose correlates are unclear in many extinct groups (especially those with ever-growing teeth such as notoungulates, a very diverse group of extinct hoofed mammals). Building on our preliminary investigations, we will use two alternative methods of dietary reconstruction: low-magnification enamel microwear (examining small pits and scratches on a tooth?s surface) and mesowear (assessing macroscopic wear and tooth cusp shape). By gathering data that are essentially hypsodonty-independent, this study will test the reliability of hypsodonty for inferring diet in extinct South American mammals and, by extension, other extinct groups. Our study will be the first direct analysis of diet for many of the extinct families under consideration, and will include the first investigation of microwear in living caviomorph rodents. We will also investigate the relationship between incisor morphology and diet in living caviomorph rodents to test whether incisor morphology can give clues to diet in extinct rodent species. Other studies have correlated aspects of incisor morphology with diet in other rodent groups, but none has yet examined variation in this particular group in relation to diet. Caviomorphs are quite are unlike ?typical? rats and mice and have been hypothesized to fill the ecological roles occupied by rabbits and various hoofed mammals on other continents. Results of our project will be incorporated into exhibits at the Cleveland Museum of Natural History and will be highlighted in a new mammal diversity and evolution course at Case Western Reserve University. This project will promote the careers of two young investigators, and will increase participation of underrepresented groups in the scientific process through a one-day museum-based teacher training program for public high school teachers in the Cleveland area; this training program will use our research on South American mammals to create lesson plans for teaching fundamentals of paleontology research to 10th grade students. We will broadly disseminate results of this research through publication in scientific journals, public lectures at universities and museums and presentations at scientific meetings, and also through innovative internet resources such a new public internet archive of microwear and mesowear images.