SKELETAL FOSSIL DIVERSITY AND ABUNDANCE ACROSS THE GREAT ORDOVICIAN BIODIVERSIFICATION EVENT (GOBE), POGONIP GROUP, ARROW CANYON RANGE, NEVADA

Abstract The Great Ordovician Biodiversification Event (GOBE) describes an interval of elevated diversification across the Middle and Late Ordovician against a backdrop of longer-term increases in biodiversity extending back to the Early Ordovician. Here, we report skeletal fossil abundance data from the Lower and Middle Ordovician Pogonip Group in the Arrow Canyon Range, Nevada to examine how skeletal biomass changed across this interval of substantial global diversification. Ninety-five samples of representative lithologies from informal units Opb, Opc, Opd, Ope, and Opf were point-counted to quantify skeletal abundance and diversity. We find that fossil biodiversity increases during the Lower Ordovician and across the Lower–Middle Ordovician transition in the Pogonip Group, suggesting that the higher diversification rates characteristic of the GOBE may be reflected in this locality in the Floian and Dapingian. Mean skeletal fossil abundance for each unit ranges from 8 to 14% and does not demonstrate a monotonic temporal increase across the full Pogonip Group. However, compared with Cambrian and Upper Ordovician data from other Laurentian localities, skeletal abundance in the Arrow Canyon Range supports a broad trend of increasing calcareous animal fossil abundance in the early Paleozoic. In sum, despite documented increases in biodiversity across the GOBE, skeletal abundance is variable in the Arrow Canyon Range, likely reflecting the influence of local environmental controls. This work illustrates the importance of examining animal abundance in strata representing various environments that span the Lower and Middle Ordovician across the globe to reconstruct the dynamics of how skeletal biomass and diversity changed through this critical diversification event.