Climate change and the selective signature of the Late Ordovician mass extinction

Abstract

Selectivity patterns provide insights into the causes of ancient extinction events. The Late Ordovician mass extinction was related to Gondwanan glaciation; however, it is still unclear whether elevated extinction rates were attributable to record failure, habitat loss, or climatic cooling. We examined Middle Ordovician-Early Silurian North American fossil occurrences within a spatiotemporally explicit stratigraphic framework that allowed us to quantify rock record effects on a per-taxon basis and assay the interplay of macrostratigraphic and macroecological variables in determining extinction risk. Genera that had large proportions of their observed geographic ranges affected by stratigraphic truncation or environmental shifts at the end of the Katian stage were particularly hard hit. The duration of the subsequent sampling gaps had little effect on extinction risk, suggesting that this extinction pulse cannot be entirely attributed to rock record failure; rather, it was caused, in part, by habitat loss. Extinction risk at this time was also strongly influenced by the maximum paleolatitude at which a genus had previously been sampled, a macroecological trait linked to thermal tolerance. A model trained on the relationship between 16 explanatory variables and extinction patterns during the early Katian interval substantially underestimates the extinction of exclusively tropical taxa during the late Katian interval. These results indicate that glacioeustatic sea-level fall and tropical ocean cooling played important roles in the first pulse of the Late Ordovician mass extinction in Laurentia.climate change | stratigraphy | sea level | Hirnantian | marine invertebrates T he Late Ordovician Mass Extinction (LOME) was the first of the "Big Five" Phanerozoic mass extinctions, and it eliminated an estimated 61% of marine genera globally (1). The LOME stands out among major mass extinctions in being unambiguously linked to climate change. The primary pulse of extinction near the Katian/Hirnantian stage boundary closely coincided with the rapid growth of south polar ice sheets on Gondwana (1-4). Expansion of continental ice sheets was accompanied by substantial cooling of the tropical oceans (5, 6), a major perturbation of the global carbon cycle (7-9) and a large drop in eustatic sea level (2, 5, 10, 11), which drained the vast cratonic seaways that characterized the Late Ordovician world (12). Extinction rates were particularly high around the tropical paleocontinent of Laurentia (13) where retreat of cratonic seas drove a sharp reduction in the area of preserved sedimentary rock between Katian and Hirnantian time (Fig. 1).The complex interrelated events surrounding the LOME exemplify a classic problem in paleobiology. Peaks in apparent extinction rate (14) are commonly associated with major gaps in the stratigraphic record or rapid changes in depositional environments. It is not always clear, however, whether these peaks simply reflect the spurious accumulation of last appearances at hiatal surfaces and lithofacies j...

Graptolite community responses to global climate change and the Late Ordovician mass extinction

“…Furthermore, relative sea level rise during the latest D. mirus interval did not restore the previous community structures. These features indicate that the observed changes in graptolite community structure were not a sampling artifact caused by shifting facies and eustatic sea level fall (43) and reinforce suggestions that carefully controlled analysis across multiple depositional environments is essential to understand the common cause effects of sea level and environmental changes on mass extinction (43,44).…”

Biogeographic and bathymetric determinants of brachiopod extinction and survival during the Late Ordovician mass extinction

“…The sharp decline in the amount of preserved sedimentary rock between the Katian and the Hirnantian [13] raises the possibility that some of the apparent extinction during the first pulse of the LOME reflects record failure rather than reflecting true extinction. No existing database captures the global distribution of sedimentary rock with spatio-temporal resolution sufficient to compare directly with our database.…”

“…However, substantial uncertainty remains regarding the mechanisms of extinction-there are many ways in which climatic transitions and associated oceanographic changes could potentially lead to elevated extinctions, particularly through habitat loss [5,8,11]. Previous studies of the LOME have implicated two major drivers of extinction: (i) loss of species inhabiting shallow cratonic seaways that drained as Gondwanan glaciers grew; and (ii) loss of species with narrow and/or relatively warm thermal tolerance ranges as the polar front advanced and the latitudinal temperature gradient steepened [12,13]. Late Ordovician -Early Silurian climatic events seem also to have been associated with major changes in oceanographic circulation, productivity and oxygenation of outer shelf and slope settings [6,14].…”

Evolution caused by extreme events

“…For example, mass extinction near the end of the Ordovician Period, some 445 million years ago, is associated with a short-lived ice age [82]. Why did Ordovician ice sheets result in widespread species loss, when relatively few marine extinctions are associated with Pleistocene glaciation?…”

“…R. Soc. B 372: 20160146 effective migration in the face of climate change than was probable in the Ordovician [82].…”