Global factors constrain body size trends across the Great Ordovician Biodiversification Event at a regional scale: a case study from the Arbuckle Mountains of Oklahoma

The Great Ordovician Biodiversification Event (GOBE) records a global
increase in marine biodiversity which reached maximum diversification
rates during the Middle Ordovician. The degree to which the drivers of the
GOBE are regional or global is a question which must be addressed through
analysis of regional data. In this study, stratigraphically constrained
field-based data from the Middle Ordovician Simpson Group of Oklahoma were
collected to identify temporal trends in body volume and determine whether
body volume trends are more closely associated regional or global
environmental and diversity changes. Volume increase was primarily
associated with global-scale factors such as age, δ18O (temperature),
87Sr/86Sr (tectonics), and taxonomic diversity trends; whereas local-scale
factors of Δ13C (carbon cycle) and lithologic trends were more weakly
associated with local volume trends. Notably, all factors had a non-zero
influence over brachiopod volume, indicating that local diversification
was driven by multifaceted interactions among abiotic and biotic controls.
These results support the argument that Ordovician diversification
included a substantial biotic shift during the Middle Ordovician and
support the hypothesis that global factors were dominant influencing
diversification patterns during the main phase of the GOBE. This dataset
includes stratigraphic columns, ltihology, shell measurements, and
isotopic data used in the analysis.