What is the role of reef structure in driving high rates of speciation among reef fauna throughout the Phanerozoic? One potential explanation is that the complex structure of reefs could allow for finer spatial partitioning, thus facilitating speciation and accommodating high diversity. My dissertation project critically addresses this idea by testing for such changes among encrusting organisms across the Middle Ordovician, when reefs transition from microbial to metazoan construction. Fundamental to my analysis, however, is objective, quantitative description of topographic complexity in reefs of diverse types. These measures must accommodate the progressive introduction of complex facies relationships and novel framework elements such as sponges and stromatoporoids, during the study period.

Unfortunately, traditional carbonate classification schemes focus on fabric at the scale of thin-sections, ignoring larger-scale features such as the size, connectivity, and patchiness of cavity space between skeletal elements. We also lack a formalized system of characterizing facies relationships that emerge at >1m scales by the Late Ordovician. To quantify heterogeneity at these intermediate to large scales, I am adapting methods from forest ecology studies. I will compare an array of these heterogeneity measures across individual bioherms and between bioherms of different construction and age within the Ordovician, and use these measures to inform census data of encrusting organisms. In addition to evaluating cavity structure at an under-examined set of scales, this project will provide greater insight into early biotic controls on reef structure and the role of such structural heterogeneity on driving evolution in the reef environment.