DISSERTATION RESEARCH: Phytolith Undulation Index: Developing a new proxy for tracking habitat openness in the Eocene-Miocene of Gran Barranca, Argentina

这项研究旨在开发一种新的方法来确定化石记录中的植被是开放的(例如草原)还是封闭的(森林)，这种方法是通过被称为植硅体的充满二氧化硅的植物细胞的形状来确定的。叶子中表皮细胞的形状取决于叶子发育时接受多少阳光。生长在有树荫的森林地面上的植物比在阳光充足的情况下生长的植物有更多的波状或波浪状的表皮细胞。在化石记录中，一些植物的表皮细胞被保存为二氧化硅铸件。这项研究将开发一种方法，通过研究从开放和封闭的植被(稀树草原到多层热带雨林)的现代土壤中收集的植物硅体，从数学上计算植被开放度(以叶面积指数-LAI衡量)。我们将使用这个数学关系从植物化石中解释数百万年前开阔的植被是如何形成的。具体地说，我们将研究在始新世-中新世(4200万-1800万年前)，随着全球气候的变化和阿根廷巴塔哥尼亚火山频繁喷发，植被开放程度是如何变化的。我们还将比较我们的植被开放记录与哺乳动物化石的记录，以测试以植物为食的动物是否通过牙齿的进化变化(增加树冠高度)来适应日益开放的地形。叶面积指数的测量在现代生态学研究和气候模拟中具有重要意义。有了一种根据化石记录估计LAI的方法，科学家就可以了解古代植被的结构，并可以更直接地比较现代和古代植被，这对于研究环境如何随着时间的变化至关重要。这项研究为本科生提供参与研究的机会，为教育和研究提供在线资源，并将通过博物馆展览向公众开放。

This study aims to develop a new method for determining whether vegetation was open (for example steppe) or closed (forest) in the fossil record from the shape of silica-filled plant cells called phytoliths. The shape of epidermal cells in leaves depends on how much sunlight a leaf receives when it develops. Plants growing on shaded forest floors have more undulated, or wavy epidermal cells than plants growing in full sun. Epidermal cells from some plants are preserved as silica casts in the fossil record. This study will develop a way to calculate mathematically vegetation openness (measured as Leaf Area Index-LAI) from how undulated epidermal phytoliths are, by examining phytoliths collected from modern soils from open and closed vegetation (savanna to multi-tiered rainforest). We will use this mathematical relationship to interpret from fossil phytoliths how open vegetation was millions of years ago. Specifically, we will look at how vegetation openness changed with shifts in global climate and frequent volcanic eruptions in Patagonia, Argentina during the Eocene-Miocene (42-18 million years ago). We will also compare our record of vegetation openness with the record of fossil mammals to test whether plant-eating animals were adapting to increasingly open landscapes through evolutionary changes in their teeth (increasing crown height). LAI measurements are important in modern ecological studies and in climate modeling. Having a method for estimating LAI from the fossil record allows scientists to understand the structure of ancient vegetation, and permits more direct comparisons between modern and ancient vegetation, which is vital for investigating how environments have changed over time. This study offers opportunities for undergraduates to become involved in research, provides online resources for education and research and will be accessible for the public through museum exhibitions.