PHYLOGENETIC STRUCTURE OF COMMUNITY ASSEMBLY AND NICHE PARTITIONING: A CASE STUDY USING CRINOIDS FROM THE BRECHIN LAGERSTÄTTE (UPPER ORDOVICIAN, ONTARIO)

Integrating phylogenetics with paleoecology can provide valuable context for understanding how patterns of community assembly are generated and for evaluating ecological niche partitioning among closely related species. However, the lack of robust phylogenies and/or paleoecological data often precluded studies of this nature, particularly among fossil invertebrates. Recent advances in resolving the crinoid tree of life have produced high-resolution phylogenies for Ordovician crinoids, facilitating the investigation of macroevolutionary questions using tree-based comparative methods. Likewise, crinoids offer a unique ecological window into understanding functional diversity and community structure because crinoids fossils commonly preserve anatomical features that direct relate to feeding ecology. Notably, niche occupation among crinoids can be inferred via comparative analysis of morphologic traits related to the size, shape, and structure of the filtration fan and overall height above the sea floor (tiering). Together, these two perspectives (i.e., historical/phylogenetic and functional/ecologic) provide a valuable framework for assessing processes that shape community assembly through either promotion or suppression of niche partitioning. Here, we apply phylogenetic community paleoecology to study one of the most taxonomically diverse and oldest ecologically complex crinoid communities, the Upper Ordovician “Brechin Lagerstätte.”

We collected and analyzed eco-morphological trait data from all 36 crinoid species known from the Brechin Lagerstätte to (1) characterize functional morphology and niche occupation of crinoid taxa and (2) assess community structure and faunal gradients. A species-level phylogeny of Ordovician crinoids was incorporated to assess the structure of crinoid communities in terms of niche occupation and how it is partitioned within and among clades. Through the integration of paleoecological and phylogenetic data, we also evaluated whether traits relating to niche differentiation are phylogenetically conserved or overdispersed among members of the crinoid community and address the degree to which competition versus habitat filtering were responsible for shaping and maintaining community structure.