When Physical Form and DNA Collide: Resolving the Evolutionary Tree of Crinoidea

Grant Winners

Dean

Abstract

Crinoids--sea lilies and feather stars--are one of the five major groups of living echinoderms. (Sea stars and sea urchins are others.) Despite their exclusively suspension-feeding lifestyle, they are diverse and often abundant in many marine habitats, from shallow reefs, where they may reach densities >100 individuals per square meter, to depths greater than 9,000 meters. Because 80-90% of the crinoid body consists of a calcium carbonate skeleton, these animals have left an enormous fossil record. Although they almost became extinct at the end of the Paleozoic Era, 251 million years ago, the surviving lineage--the Articulata--subsequently diversified into eight orders and 72 families, almost half of which survive in modern seas as ~650 species. Although recent analyses based on DNA sequences alone have generated evolutionary trees that support some taxonomic groups based on physical form (morphology), they have exploded others. As a result, many characters traditionally used to distinguish various crinoid groups no longer appear to be valid. This study will examine post-Paleozoic crinoids in detail and, for the first time, apply modern phylogenetic methods to reconstruct their evolutionary history by using a combination of morphology of both living and fossil forms, and molecular data. Methods will include both light and scanning electron microscopy, focusing on recognition of characters that will reconcile morphological and molecular conflicts. The results will permit a more accurate assessment of crinoid biodiversity (e.g., for incorporation into investigations of many marine environments) and evolution (e.g., permitting paleontologists to more accurately assess crinoid-bearing stratigraphic sequences and patterns over geological time). Results will also provide a foundation for extramural proposals.