Did the amalgamation of continents drive the end Ordovician mass extinctions?

Global biodiversity has been punctuated throughout the Phanerozoic by extinction events that vary in their degree of intensity and devastation. The mass extinction event that occurred at the end of the Ordovician Period rapidly removed a wide range of species. Because taxonomic loss occurred during an ice age, this is believed to have initiated the extinctions and thus, these extinctions have often been viewed as a deep time analogue to the loss in species diversity during the present day glacial interval. The current study, however, indicates that temperature – though arguably being a trigger – was not the sole reason for the crisis. Based on a large, bibliographic database of rhynchonelliform brachiopods that specifically operates within very narrow time-slices where every locality has been precisely georeferenced for the Upper Ordovician–Lower Silurian interval, we show that the extinctions were not uniformly distributed, nor was the succeeding recovery. Here we argue that changing plate tectonic configurations during the Ordovician–Silurian interval may have exerted a primary control on biotic extinction and recovery. In particular the proximity and ultimate loss of microcontinents and associated smaller terranes around Laurentia may have restricted shelf and slope habitats during the latest Ordovician but, nevertheless, in a contracted Iapetus Ocean, provided migration routes to help drive a diachronous early Silurian recovery. The conclusion that plate tectonics was a primary factor controlling the extent of the extinctions and the subsequent diversity rebound, demonstrates that a reduction in gamma-diversity was perhaps the most important manifestation of the end Ordovician crisis and further raises the question whether this could be applied to other large Phanerozoic perturbations in biodiversity levels.