Phylogenetic Relationships Among Spire-bearing Articulate Brachiopods

腕足类是令人着迷但却鲜为人知的双壳类海洋动物。它们看起来至少在外表上与文蛤相似，但只是在谱系意义上有远亲关系。尽管腕足类在今天并不常见，但除了新西兰和澳大利亚的部分地区外，它们在2.5亿多年前的古生代就很常见，种类繁多，是古生代海洋生物群的重要组成部分。出于这个原因，古生物学家对了解它们的生态、形态、生长和行为以及它们的时间和地理分布很感兴趣，部分原因是为了了解它们的衰落和濒临灭绝。加州大学戴维斯分校(University Of California At Davis)的桑德拉·卡尔森(Sandra Carlson)博士正在研究尖顶关节腕足类，它们的瓣膜内有独特的结构，看起来很像两个锥形弹簧，与获取食物和氧气以及繁殖行为有关。目前对这些生物体的分类表明，这些结构只进化了一次，但卡尔森博士的初步工作表明，情况不太可能是这样。如果带有尖顶的腕足类动物已经进化了几次，那么将它们放在一个单一的分类学类群中会混淆它们的进化史，并限制了对导致尖顶进化的生态因素的研究。研究该化石和现存生物的其他形态特征，将有助于完善腕足类的分类和系统发育，并有助于了解它们在古生代的地质起落。

Brachiopods are fascinating but poorly understood bivalved marine animals. They look similar to clams, at least externally, but are only distantly related in a genealogical sense. Even though brachiopods are not commonly found along seashores today, except in parts of New Zealand and Australia, they were common and diverse over 250 million years ago in the Paleozoic Era and were important elements of the Paleozoic marine biota. For this reason, paleontologists are interested in learning about aspects of their ecology, morphology, growth and behavior, and their temporal and geographic distribution, in part to understand their decline and near extinction. Dr. Sandra Carlson of the University of California at Davis is studying the spire-bearing articulate brachiopods, those bearing distinctive structures inside their valves that look much like two cone-shaped springs and that are involved in obtaining food and oxygen and in reproductive behaviors. The current classification of these organisms suggests that these structures have evolved only once, but preliminary work by Dr. Carlson indicates that is not likely the case. If spire- bearing brachiopods have evolved several times, then placing them together in a single taxonomic group confuses their evolutionary history and constrains work on ecological factors responsible for spire evolution. Study of other morphological features of the fossil and extant organisms will help improve the classification and phylogeny of brachiopods, and help in understanding their geological rise and fall in the Paleozoic.