Bryozoans are a group of colony-forming animals with a rich fossil record on account of their resistant, chalky skeletons. This paper is a preliminary study of extinctions and originations of bryozoans over the past 100 million years. Limitations in the database result from the scant study of bryozoans compared with many other fossil groups. Nevertheless, we are able to show that, for bryozoan genera belonging to two separate groups (cheilostomes and cyclostomes), the greatest intensity of extinction occurred during the Maastrichtian stage of geological time and may correspond with the famous K-T mass extinction seen in many other animals and plants at this time. A second phase of bryozoan extinction followed almost immediately, during or at the end of the Danian stage of geological time. Most bryozoans of this age are known from shallow water limestone environments in northwest Europe and the demise of these environments probably explains the Danian extinction. A third but less intense phase of extinction occurred during the Priabonian age at the end of the Eocene epoch of geological time, about 33 million years ago, corresponding with yet another time of global extinction in numerous other groups of organisms. Bryozoans with upright colonies (as opposed to encrusting colonies closely adpressed to a hard surface) were especially hard hit in the Priabonian. The number of bryozoans present in each successive interval of geological time depends on the interplay between extinction and origination rates. For both groups of bryozoans, origination rates were high during the Late Cretaceous (between about 100 and 65 million years ago) and both consequently increased in diversity. This pattern was continued by cheilostomes in the Cenozoic (65 million years ago to present day) but not by cyclostomes whose origination rate dropped immediately in the earliest Cenozoic causing diversity to level-off or even dip. Bryozoans are particularly interesting in understanding evolutionary dynamics because of the related and yet distinct evolutionary histories evident in the two different groups, despite the fact that the groups contain species having a very similar range of ecologies. In fact, our analysis of the temporal patterns of extinction and origination rates in cheilostomes yields results consistent with the Sepkoski et al. (2000) coupled-logistic model of cheilostome/cyclostome clade interaction. This model attributed the flat Cenozoic diversity history of cyclostomes to suppression of cyclostome originations by the competitively interacting cheilostomes rather than an increase in cyclostome extinctions.