Dissertation Research: The Origin and Spread of Grass-dominated Ecosystems during the Late Tertiary of North America and How it Relates to the Evolution of Hypsodonty in Ungulates

建议：Deb-1-0104975PI：N.C.Arens&Amp；C.Stromberg Dissertation Research：北美晚第三纪以草为主的生态系统的起源和传播，以及它与有蹄类动物的高地生物进化的关系。在中新世(18-1500万年前)，马、骆驼和犀牛等动物独立地进化出被解释为适应草原的特征。这些特征包括用于加工粗粮的高冠面颊牙齿和用于跑步的长腿。如果这些特征是真正的适应，就必须证明这些特征是在草原出现后同一时间或不久出现的。这个问题很难解决，因为北美大多数保存有动物化石的地方都没有植物化石。结合其他证据，例如来自花粉或古土壤的证据，使用一种新型的植物化石--植硅体--将使这一问题得以避免。植硅体是在植物组织中产生的微小硅体，可以确定生命形式(例如，草、灌木和乔木)。拟议的研究将为三个一般问题提供答案。首先，北美是否有详细的植物硅石记录，可以用来重建与动物化石相关的植被类型？第二，草原最早出现在大平原的时间和地点，以及它们是如何传播的？第三，向以草为主的生态系统的转变是在草原上与生命相关的动物特征的进化之前、同时还是之后发生的？

Proposal: DEB-1-0104975PI: N. C. Arens & C. StrombergDissertation Research: The origin and spread of grass-dominated ecosystems during the late Tertiary of North America and how it relates to the evolution of hypsodonty in ungulates.During the Miocene (18-15 million years ago), animals such as horses, camels, and rhinos independently evolved traits interpreted as adaptations to grasslands. These traits included high-crowned cheek teeth for processing coarse food and long legs for running. If these traits are truely adaptations, one must show that the traits arose at the same time or soon after grasslands appeared. This problem is difficult because plant fossils are absent in most places in North America where fossil animals are preserved. In conjunction with other evidence, such as those derived from pollen or paleosols, the use of a new type of plant fossil - phytoliths - will allow this problem to be circumvented. Phytoliths are microscopic silica bodies produced within the tissue of plants that allow the determination of life form (e.g., grasses versus shrubs versus tree). The proposed research will provide answers to three general questions. First, does a detailed record of phytoliths exist in North America that can be used to reconstruct vegetation type associated with animal fossils? Second, when and where do grasslands first appear in the Great Plains and how do they spread? Third, does the change to grass-dominated ecosystems happen before, coincident with, or after the evolution of animal traits associated with life in grasslands?