Changes in the diversity and environmental distribution of marine stenolaemate bryozoans through the Permian to Early Jurassic interval are used to constrain the timing of environmental stress, determine the degree to which it differentially affected marine settings, evaluate its long-term impact on bryozoan evolution, and review current extinction scenarios for the end-Permian and end-Triassic crises. Results indicate that the end-Permian and end-Triassic mass extinctions were characterized by protracted intervals of environmental stress that initiated during the end-Guadalupian event several million years prior to the end-Permian, and again during the Norian stage prior to the end-Triassic. Environmental degradation lasted into the Early Triassic and Early Jurassic, hampering the recovery of marine communities. Prior to both extinctions offshore settings were affected first, suggesting environmental stress resulted from the gradual encroachment of a deep-water phenomenon onto the shelves, thus precluding catastrophic events as kill mechanisms and supporting long-term oceanographic processes such as widespread euxinia resulting from massive volcanism and global warming. The end-Permian event was the most influential for bryozoans, triggering a permanent change in their paleoenvironmental preferences from onshore to mid-shelf settings and a taxonomic switch between stenolaemate and gymnolaemate bryozoans. The taxonomic switch itself initiated a gradual shift in the overall morphological composition of bryozoan assemblages between erect-dominated Paleozoic communities and encruster-dominated Mesozoic communities. Major changes in the paleoenvironmental preferences of bryozoans were also coupled with fluctuations in their diversity.