Schuster, A.; Canfield, D. E.

Sponges (phylum Porifera) have been essential to marine ecosystems for over 600 million years, contributing to nutrient cycling, reef building, and ecological stability. Despite their evolutionary importance, the drivers of their diversity dynamics remain poorly understood. This study investigates the diversification patterns of Demospongiae, the largest class of sponges with a well documented fossil record throughout the Phanerozoic Eon (541 to 0 Ma). Using fossil occurrence data and a Bayesian framework, we modeled origination and extinction rates to understand their evolutionary history. Our findings reveal key extinction events, including three previously unrecognized events in the Cambrian, Late Silurian, and Late Jurassic, alongside known events such as the Permian Triassic and Triassic Jurassic extinctions. Notably, there was no statistical evidence for mass extinction during the Late Ordovician or Late Devonian. Additionally, Demosponges underwent a significant decline prior to the Cretaceous Paleogene extinction. To explore abiotic influences, we applied the Multivariate Birth-Death (MBD) model across all extinction events. This analysis identified correlations between major speciation and extinction events and key variables, including temperature, continental fragmentation, oxygen levels, and sea level, as well as geochemical proxies such as sulfur and strontium, which may reflect underlying drivers like anoxia, weathering, or tectonic activity. Temperature and oxygen levels, in particular, correlated with speciation and extinction during the Permian-Triassic extinction. These findings underscore the role of environmental fluctuations in shaping demosponge diversity and highlight the complex interplay between changes in abiotic factors and sponge evolution. Our work provides critical insights into the factors driving sponge biodiversity and offers perspectives on how modern sponges might respond to ongoing climate change.