Phylogenetic Relationships Among Spire-bearing Articulate Brachiopods

腕足动物是一种令人着迷但人们对双壳海洋动物知之甚少的动物。 它们看起来与蛤相似，至少在外观上如此，但只是在谱系意义上有远亲关系。 尽管除了新西兰和澳大利亚的部分地区外，腕足动物在今天的海岸上并不常见，但它们在 2.5 亿年前的古生代时期就很常见且多样化，并且是古生代海洋生物群的重要组成部分。 因此，古生物学家有兴趣了解它们的生态、形态、生长和行为，以及它们的时间和地理分布，部分是为了了解它们的衰落和濒临灭绝。 加州大学戴维斯分校的桑德拉·卡尔森博士正在研究带有尖顶的关节腕足动物，这些腕足动物的瓣膜内部具有独特的结构，看起来很像两个锥形弹簧，参与获取食物和氧气以及繁殖行为。 这些生物体目前的分类表明这些结构只进化了一次，但卡尔森博士的初步研究表明情况并非如此。 如果带尖顶的腕足动物已经进化了好几次，那么将它们放在一个分类群中就会混淆它们的进化历史，并限制对尖顶进化的生态因素的研究。 对化石和现存生物的其他形态特征的研究将有助于完善腕足动物的分类和系统发育，并有助于了解它们在古生代的地质兴衰。

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.