CONSTRAINING MORPHOLOGICAL CHANGE ACROSS THE GREAT ORDOVICIAN BIODIVERSIFICATION EVENT: A CASE STUDY FROM THE ARBUCKLE MOUNTAINS OF OKLAHOMA

The Great Ordovician Biodiversification Event (GOBE) was a global increase in marine biodiversity, which peaked around 450 million years ago and established the foundation of modern marine ecosystems. Articulated brachiopods represent a key group through which we can study the mechanisms of this pivotal event. Prior studies have compiled brachiopod occurrence data in order to plot diversity trajectories during the GOBE; however, these studies often fail to fully consider how environmental change impacts changes in species diversity. Due to excellent temporal resolution and fossil preservation, the Lower to Middle Ordovician strata of Oklahoma provide an exceptional framework through to analyze morphological change within a detailed stratigraphic context. This framework can then be used to better understand the relationship between environment and brachiopod morphology, and thus better constrain the factors driving diversification across the GOBE.

Stratigraphically constrained field-based data will be used to relate changes in brachiopod morphology with associated environmental change in a temporal context. Recent analyses indicate that the primary phase of the GOBE occurred during the Darriwilian Age and is expressed in the McLish Formation of the Simpson Group; thus, analysis will focus on rocks from before and during this interval including the West Spring Creek through Bromide formations. Detailed morphological measurements, including maximum height, width, and volume, will be made for brachiopods from each stratigraphic unit at a bedding plane level of resolution. Potential trends in these measurements will be analyzed statistically with respect to temporal and environmental trends. Study of representative brachiopod specimens in museum collections prior to field work will provide a framework for expected morphology.

Expected correlations between brachiopod morphology and stratigraphy include size and volume increase through time, regardless of environmental change; however, brachiopod body size may be most tightly correlated with substrate type. Constraining these relationships will provide insight into environmental influence on brachiopod diversity and will help broaden our understanding of diversification patterns and processes during the GOBE.