CONSTRAINING BODY SIZE TRENDS ACROSS THE GREAT ORDOVICIAN BIODIVERSIFICATION EVENT AND EVALUATING POTENTIAL DRIVERS OF DIVERSIFICATION: 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. Increased body size has been recorded during the GOBE, but this pattern has not been fully examined within the context of environmental and diversity change. In this study, the outstanding record of articulated brachiopods in the Lower to Middle Ordovician strata of Oklahoma is used to examine how body volume changes through time in this key clade within a detailed stratigraphic and geochemical framework. This framework can 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 were used to relate changes in brachiopod size and volume with associated environmental change. Recent analyses indicate that the primary phase of the GOBE occurred during the Darriwilian Age; thus, analysis focused on rocks aged before and during this interval including the Joins, Oil Creek, and McLish formations. Maximum height and width measurements were collected on exposed brachiopod valves of each stratigraphic unit at a bedding plane level of resolution. Lithologic facies data were recorded for each bedding plane, and stratigraphic sections were measured to build a stratigraphic framework for morphological measurements. Trends in shell volume were analyzed separately via Time Series Analysis. Morphological data were then analyzed alongside lithologic, taxonomic diversity, and geochemical trend data using a Boosted Regression Model.

Results of the Time Series Analysis indicate that average brachiopod volume increased through time, with the primary volume increase occurring shortly after the main GOBE pulse. Analyses indicate that volume trends are most tightly correlated to taxonomic diversity trends; conversely, substrate type has a less impactful influence over volume size trends.