Transient metazoan reefs in the aftermath of the end-Permian mass extinction

Recovery from the devastating Permian–Triassic mass extinction about 252 million years ago is usually assumed to have spanned the entire 5 million years of the Early Triassic epoch1, 2. The post-crisis interval was characterized by large-scale fluctuations of the global carbon cycle and harsh marine conditions, including a combination of ocean acidification, euxinia, and fluctuating productivity3. During this interval, metazoan-dominated reefs are thought to have been replaced by microbial deposits that are considered the hallmark of the Early Triassic4, 5, 6, 7. Here we use field and microscopic investigations to document Early Triassic bioaccumulations and reefs from the western USA that comprise of various sponges and serpulids associated with microbialites and other eukaryotic benthic organisms. These metazoan-rich reefs were formed only 1.5 million years after the extinction, in contrast to previous suggestions of a much delayed recovery of complex benthic communities. We conclude that the predominance of microbial reefs following the mass extinction is restricted to short intervals of the earliest Triassic. We suggest that metazoan reef building continued throughout the Early Triassic wherever permitted by environmental conditions

Lessons from the Past: Sponges and the Geological Record

Sponges have been a major part of marine ecosystems, in both shallow and deep water, from the time of the earliest animal communities. The great shifts in climate that have occurred over the past 541 million years have affected all organisms, including sponges. Although patchy knowledge of the sponge fossil record hinders recognition of trends, some general patterns are apparent. Shallow-water siliceous sponges were severely affected by glacial intervals, whereas deeper-water siliceous sponges appear to have flourished during these times. Some groups of hypercalcified sponges (such as stromatoporoids) were abundant during times of global warming and high sea level, but other groups (archaeocyathans and sphinctozoans) had their acme during times of low sea level and relatively cool climate. Overall, sponge diversity appears to have been controlled more by sea level than by climate: large-scale sponge biotas occurred at times of high sea level, when there were large areas of shallow sea.Fil: Muir, Lucy. National Museum Wales; Reino UnidoFil: Botting, Joseph P.. National Museum Wales; Reino Unido. Nanjing Institute Of Geology And Palaeontology; ChinaFil: Beresi, Matilde Sylvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin