Range and radiation of Cambrian Trilobites

Revealing the patterns and drivers of diversity in the Cambrian requires an understanding of distribution. On a dynamic Earth with uncertain palaeogeography, the understanding of range and diversity requires novel methodology and approaches. Trilobites, an extremely diverse group of arthropods, underwent important shifts in diversity and morphology throughout the Cambrian. However, the mechanisms driving their global dispersal and diversification during the early Palaeozoic remain inadequately understood. Persistent issues in studying the facilitators of distribution include morphological and life history constraints, e.g. the impact of benthic or pelagic larval stages. This uncertainty is compounded by the limitations of current palaeogeographical reconstructions. To address these issues, the Trilobite Biogeography and Ecology working group (TRiBE) applied  a novel approach to geography and reconstructed trilobite biogeographical patterns associated with their initial global radiation from throughout the Cambrian. Using phylobiogeographic methods, with the Paterson et al (2019) phylogeny, we took three approaches to area establishment and compared the resulting patterns. The results, strengthened through robust comparison of area establishment, provide insights into Cambrian trilobite ancestral geographical ranges, the frequency and type of allopatric speciation events, and the connectivity between different regions during this critical phase of euarthropod evolution. Comparison between palaeogeography, climate, and marine connectivity are examined as facilitators of a global trilobite distribution and the specialisation of the group throughout the Cambrian. This study aims to both make comment on the evolutionary success of early euarthropods, but also to highlight the influence of geographical assumptions on interpretation.