Dissertation Research: A Phylogenetic and Morphometric Analysis of Early Palezoic Archaeogastropods: An Examination of the Expansion of a Clade into Morphospace

始源胃足类出现于寒武纪晚期，并迅速扩展到包含广泛的形态。这些包括与基本腹足动物生活方式相关的大多数形态。后来在贝壳纹饰的变化中发生了轻微的形态辐射。因此，古胃足类动物提供了多种特征类型和形态水平，用于描述形态模式随时间的变化。本项目包括早古生代古胃足类动物的系统发育和形态计量学分析。这些方法将用于比较三种不同形态空间中姐妹种差异的典型形态距离：1)基于类群起源处出现的12个“基壳”特征；2)一种以贝壳纹饰为基础，直到晚奥陶世才出现在大多数亚群中；第三种是基于被认为具有基本功能效用的性格复合体。利用纹饰来比较“早期”和“后期”壳性状中枝扩展的时间模式，将提供信息，说明枝间和枝内变异是否更多地取决于枝辐射的时间（即外在因素），还是取决于区分它们的性状状态的年龄（即内在因素）。在特征复合体的形态空间中研究系统发育模式将以一种更有意义的生物学方式描述古腹足类动物的辐射，也为测试进化枝的非随机分类提供了一个额外的形态“水平”。

The Archaeogastropoda appeared in the Late Cambrian and rapidly radiated to encompass a wide range of morphologies. These included most of the morphotypes associated with basic gastropod lifestyles. A minor morphologic radiation occurred later with changes in shell ornamentation. Archaeogastropods thus offer multiple character types and morphologic levels for describing changes through time in the patterns of morphology. This project includes both phylogenetic and morphometric analyses of Early Paleozoic archaeogastropods. These approaches will be used to compare typical morphological distances of differences between sister species in three different morphospaces: 1) one based upon twelve "basic-shell" characters appearing at the group's origin; 2) one based upon shell ornamentation, which did not appear in most subgroups until the Late Ordovician; and 3) one based upon character complexes thought to have a basic functional utility. Using ornamentation to compare the temporal patterns of clade expansion in both "early" and "later" shell characters will provide information on whether inter- and intraclade variation depend more on the time in which the clade radiated (i.e., extrinsic factors) or upon the ages of the character states distinguishing them (i.e., intrinsic factors). Examining phylogenetic patterns in a morphospace of character complexes will describe the archaeogastgropod radiation in a biologically more meaningful manner and also provide an additional morphologic "level" to test for non-random sorting of clades.