MACROSTRATIGRAPHIC AND MACROECOLOGICAL DETERMINANTS OF EXTINCTION RISK DURING THE LATE ORDOVICIAN MASS EXTINCTION

Selectivity patterns provide important insights into the drivers of ancient extinction events. The Late Ordovician mass extinction is thought to be related to climatic cooling and Gondwanan glaciation, but a clear selective fingerprint has been hard to identify and understanding the role of climate change has been complicated by issues of rock record loss. To provide fresh constraints on this problem, we matched Late Ordovician-Early Silurian North American fossil occurrence records from the the Paleobiology Database (PaleoDB) to spatiotemporally explicit sedimentary rock packages in the Macrostrat Database. This integrated framework allows us to quantify rock record effects on a per-taxon basis and assay the interplay of macrostratigraphic and ecological variables in determining extinction risk. There is a major pulse of stratigraphic truncations at the end of the Katian Stage, consistent with other stratigraphic and geochemical lines of evidence for a major glacioeustatically forced regression at this time. Genus extinction rates also peak at the end of of the Katian, and genera that had large proportions of their ranges affected by stratigraphic truncation and/or shifts in lithofacies distribution exhibit the highest extinction rates. Genera with prior occurrences at high paleolatitude exhibit reduced extinction risk during this interval, even after controlling for the covariation between maximum latitude, geographic range, endemicity, and genus age. These patterns strongly suggest that both eustatically-forced habitat losses and cooling of the tropical oceans played important roles in the Late Ordovician mass extinction in Laurentia. “Background” extinction selectivity patterns before and after the mass extinction interval are complex but illustrate trends commonly observed in studies of the marine invertebrate record - emergent macroecological traits such as geographic range strongly influence extinction risk whereas autecological traits play a comparatively minor role after controlling for phylogeny.