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

太古代腹足类出现在晚寒武世，并迅速辐射到包括多种形态。这些包括与腹足类基本生活方式相关的大多数形态类型。后来出现了轻微的形态辐射，贝壳装饰也发生了变化。因此，考古腹足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。该项目包括对早古生代考古腹足类的系统发育和形态计量学分析。这些方法将被用来比较三个不同形态空间中姐妹种之间的典型形态距离：1)基于12个出现在种群起源处的“基本壳”特征；2)基于贝壳装饰的特征，直到晚奥陶世才出现在大多数亚群中；以及3)基于被认为具有基本功能的字符复合体。使用装饰来比较“早期”和“后期”贝壳角色的分支扩展的时间模式，将提供信息，即分支间和分支内的变化是否更多地取决于分支辐射的时间(即，外部因素)或区分它们的角色状态的年龄(即，内在因素)。在一个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生物学意义的方式描述始祖足目动物的辐射，并提供一个额外的形态“水平”来测试支系的非随机分类。

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.