Exploring changes in trilobite provincialism across the Cambrian redlichiid–olenellid extinction

Trilobite faunal provincialism is embedded in our understanding of early Cambrian palaeobiogeography, with the redlichiid, olenellid and bigotinid realms observed during Cambrian Epoch 2. However, provincialism apparently became reduced in trilobites across the diachronous late Age 4 redlichiid–olenellid extinction, with many families developing cosmopolitan ranges. We analysed data from the Paleobiology Database using network analysis to determine the nature and degree of trilobite provincialism during Cambrian Epoch 2, and how this changed across the redlichiid–olenellid extinction, with the aim of constraining the drivers of such patterns (e.g. biology, tectonics) under a neutral methodological framework. Results confirm that provincialism was elevated for trilobites during Epoch 2, but that Cambrian trilobite realms were not distinct entities. Rather, they reflect a continuous gradient of faunal turnover across the early Cambrian world that is most consistent with a model of rapid radiation and dispersal. Following the demise of the Cambrian Epoch 2 realms, faunal provinciality in trilobites at the family and genus level decreased measurably, with both biological and tectonic processes possible drivers of this change. Future work should aim to refine the observations and suggestions made here by exploring such patterns in higher stratigraphic resolution and in a broader range of taxa.