Changes in calyx size of fossil crinoids

The analysis of calyx sizes of fossil crinoids has shown that the mean calyx size significantly decreased during the periods of mass extinction (during the late Ordovician, the middle-late Devonian, the Permian–Triassic boundary, the Cretaceous anoxic events). These declines were mostly governed by extinction of larger taxa, except during the Cretaceous anoxic events, when the mean size decrease was driven by origination of small-sized taxa. The analysis is based on a newly created database with measurements of 1263 Palaeozoic and Mesozoic crinoid calyces.