Environmental Controls on Late Ordovician (Katian) Crinoid Feeding Ecology

Abstract

Crinoids are an incredible model group for the study of community paleoecology, including niche space occupation, feeding ecology, and species interactions. Ecomorphological traits can be used to model resource use and niche occupation of species and to evaluate species interaction and structure within crinoid communities. The ecomorphological traits of crinoids reflect their filter-feeding habits through traits including calyx size and filtration fan area and density. To effectively model the evolution of crinoid communities over time, we must also understand the degree to which environmental factors such as habitat filtering control the distribution of crinoids within communities. In this study, I analyze the feeding ecology of crinoids from seven paleocommunities from the Katian stage of the Late Ordovician Period (453.0-445.2 Ma) to quantify the similarities and differences in crinoid feeding ecology between various sedimentary environments and evaluate relationships between crinoid ecomorphology and environment. I employ functional morphology methods to collect ecomorphological trait measurements quantify crinoid feeding ecology and niche space occupation. The results of this study present a measurable directional control by depositional environments on the feeding ecology of Katian crinoid communities. Across an environmental gradient from deep, low-energy settings to shallow, high-energy settings and a gradient from siliciclastic-predominant to carbonate-predominant settings, ecomorphological disparity increases toward the shallow, carbonate end of the gradient. Thus, I establish that habitat filtering plays a major role in controlling the ecological structure and taxonomic composition of crinoid communities by preferentially excluding species with ecological strategies that are not well-suited to certain environmental conditions.