CHANGE IN ECOSPACE UTILIZATION THROUGH THE TYPE CINCINNATIAN: A STUDY OF BIODIVERSITY PATTERNS AS A FUNCTION OF STRATIGRAPHIC RANGE, LITHOLOGY AND SAMPLE SIZE

Throughout the Phanerozoic, ecological complexity has increased in terms of how organisms spatially and functionally use the environment around them. Previous work by Bush, Bambach and Daley (Bush et al., 2007) determined there was a marked increase in the ecological living strategies, otherwise known as ecospace utilization, of organisms through time as observed between mid-Paleozoic and Cenozoic marine fossil communities.

In this research, late Ordovician (type Cincinnatian) marine fossil communities were analyzed to examine how ecospace utilization varies as a function of stratigraphic range, lithology and sample size. A dataset comprised of fossiliferous assemblages from the Kope Formation (452.5-450 Ma) were used to make ecospace utilization assessments. A series of theoretical ecospace utilization cubes were generated by classifying genera into distinct modes of life. Each genus was categorized according to their feeding mechanism, degree of motility and level of tiering above or below the sea floor.

The Kope Formation was separated into its three stratigraphic members (Economy, Southgate and McMicken) to determine how changing the magnitude of the stratigraphic interval affects perceptions of ecospace utilization. Additionally, since lithology is often considered a proxy for environment, the dataset was divided by lithology to further assess changes in ecospace utilization. Results illustrated that the modes of life from the type Cincinnatian were very similar to those observed from mid-Paleozoic communities in the work by Bush and others. The relative abundance of non-motile, surficial, suspension feeders represented the dominant mode of life compared to the other unique combinations of the tiering, motility, and feeding categories. Ecospace utilization was also observed for changes in stratigraphic scale and lithology and reveal patterns related to increasing sample size. As the number of sampled paleocommunities increases, so does the perception of ecological complexity. By understanding how ecospace is partitioned within and among communities in the well-constrained stratigraphic interval from the type Cincinnatian, one can more precisely understand how to quantify ecospace utilization at a small scale.