The role of mass extinction events in shaping the body-size dynamics of fossil crinoids

Crinoids were abundant and highly diversified marine invertebrates with a long and rich fossil record extending back to the Ordovician. Although significant progress has been made in recent years to understand their body size evolution, a complete characterization of their body-size dynamics at macroevolutionary scale and over extended time periods using up-to-date source of data remains largely unexplored. Here, we compiled a new database on crinoid calyx biovolumes throughout the Paleozoic and Mesozoic to explore their size dynamics. Despite complexities of the observed body size trajectories that differ at various taxonomic and temporal scales, a common pattern emerges from our analyses: the mean size of crinoid calyx declined significantly around most of the major extinction events (during the late Ordovician, the mid-late Devonian, the end Permian and the mid-late Cretaceous). The observed decline in the mean size of crinoid calyces is mostly governed by extinction of larger taxa, except during the mid-late Cretaceous anoxic events, when it appears to be mostly driven by origination of small-sized taxa. Overall, these findings highlight important role of extinction events in altering body size evolution