Evolutionary Radiations in Paleozoic and Mesozoic Crinoids

本研究将(1)利用明确的骨骼解剖学数据来记录古生代和中生代海百合的进化辐射；(2)通过比较海百合的整体辐射与海百合组成亚群的辐射，来检验不同分类尺度下海百合进化辐射的差异。进化辐射是化石记录中最显著的特征之一，涉及已命名分类群数量和形态多样性的大量增加。人们普遍认为，在不同的分类、时间和空间尺度上，进化辐射在时间模式或潜在机制上没有显著差异。这种观点几乎没有得到直接检验。有一些迹象表明，高等分类群（枝）和嵌套在其中的低等分类群（亚枝）的进化辐射可能存在重大差异，即亚枝内的形态多样化比它们所属的大分类群的多样化在时间上更为缓慢。然而，这些建议都是基于案例研究，并不适合测试这一想法。通过比较一个主要的无脊椎类群海百合科的古生代辐射，与与更大的海百合科同时分化的海百合科附属分支的辐射，我将检验在分类等级之间是否存在这种不一致。节理海百合的中生代辐射将提供一个额外的比较。这些结果将有助于回答有关进化的等级本质的问题，以及我们从小规模模式预测大规模进化模式的能力。在进化辐射过程中，形态多样性或差异的变化通常通过使用高级分类群（主要是纲和目）的数量来评估。有许多理由质疑这种代理的充分性。拟议的研究将使用形态学的直接量化来研究海百合的进化辐射。我将使用离散形态特征来量化海百合的形态，并将基于物种之间的净差异来测量形态差异。我将应用一些定量方法，包括“枝形”统计，来探索各种进化模型的形态预期的时间模式。拟议的研究将回答有关形态多样性在长时间进化过程中产生的问题，并将开发一个形态数据库，供其他工作人员用于研究广泛的问题，包括系统发育关系、进化速率和趋势。

Foote 9506568 This research will (1) use explicit data on skeletal anatomy to document evolutionary radiations in Paleozoic and Mesozoic crinoids, and (2) test for a proposed difference between evolutionary radiations at different taxonomic scales by comparing the radiation of crinoids as a whole to the radiations of the constituent subgroups of crinoids. Evolutionary radiations, involving substantial increases in the number of named taxa and in morphological diversity, are among the most prominent features of the fossil record. It is commonly thought that evolutionary radiations at different taxonomic, temporal, and spatial scales do not differ significantly in temporal patterns or underlying mechanisms. This perspective has scarcely been tested directly. There are some hints that there may be a major difference between the evolutionary radiations of higher taxa (clades) and the lower taxa (subclades) nested within them, namely that morphological diversification within subclades is more gradual in time than diversification of the larger clade to which they belong. However, these suggestions have been based on case studies that are not ideally suited to test this idea. By comparing the Paleozoic radiation of a major invertebrate group, the Crinoidea, to that of subsidiary crinoid clads that diversified concurrently with the larger crinoid clade, I will test for the existence of such a discordance between taxonomic ranks. The Mesozoic radiation of articulate crinoids will provide an additional comparison. The results will help to answer questions about the hierarchical nature of evolution and our ability to predict larger-scale evolutionary patterns from smaller-scale patterns. Changes in morphological diversity, or disparity, during evolutionary radiations are usually assessed by using proxies such as the number of higher taxa (mainly classes and orders). There are a number of reasons to question the adequacy of such proxies. The proposed research will use direct quantification o f morphology to study evolutionary radiations in crinoids. I will use discrete morphological characters to quantify crinoid form, and will measure morphological disparity based on the net dissimilarities among species. I will apply a number of quantitative approaches, including "clade-shape" statistics, to explore the temporal pattern of morphological expectations of various evolutionary models. The proposed research will answer questions about the generation of morphological diversity over long spans of evolutionary time, and will develop a morphological database that can be used by other workers to investigate a wide range of issues, including phylogenetic relationships, evolutionary rates, and trends.