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Abstract Ecological observations and paleontological data show that communities of organisms recur in space and time. Various observations suggest that communities largely disappear in extinction events and appear during radiations. This hypothesis, however, has not been tested on a large scale due to a lack of methods for analyzing fossil data, identifying communities, and quantifying their turnover. We demonstrate an approach for quantifying turnover of communities over the Phanerozoic Eon. Using network analysis of fossil occurrence data, we provide the first estimates of appearance and disappearance rates for marine animal paleocommunities in the 100 stages of the Phanerozoic record. Our analysis of 124,605 fossil collections (representing 25,749 living and extinct marine animal genera) shows that paleocommunity disappearance and appearance rates are generally highest in mass extinctions and recovery intervals, respectively, with rates three times greater than background levels. Although taxonomic change is, in general, a fair predictor of ecologic reorganization, the variance is high, and ecologic and taxonomic changes were episodically decoupled at times in the past. Extinction rate, therefore, is an imperfect proxy for ecologic change. The paleocommunity turnover rates suggest that efforts to assess the ecological consequences of the present-day biodiversity crisis should focus on the selectivity of extinctions and changes in the prevalence of biological interactions. 

ABSTRACT Konservat-Lagerstätten provide the most complete snapshots of ancient organisms and communities in the fossil record. In the Mesozoic, these deposits are rarely found in marine facies outside Oceanic Anoxic Event (OAE) intervals, suggesting that OAEs set the stage for exceptional fossil preservation. Although anoxia does not guarantee survival of non-biomineralized tissues or articulated skeletons, other OAE phenomena may promote their conservation. Here, we test this hypothesis with a taphonomic analysis of the Konservat-Lagerstätte in the black shales and siltstones of the Jurassic Fernie Formation at Ya Ha Tinda (Alberta, Canada). This deposit contains crustacean cuticles, coleoid gladii with ink sacs and mantle tissues, and articulated skeletons of fish, crinoids, and ichthyosaurs. The fossils were preserved in the Pliensbachian and Toarcian (Early Jurassic) when euxinic conditions were common in the area, in part, due to the ∼183 Ma Toarcian OAE. Some of the fossils contain carbonaceous material, but the majority consists of apatite minerals, and phosphatic gladii demonstrate that some animals were preserved through secondary phosphate mineralization. Phosphatization generally occurs within phosphate-rich sediment, but oceanic anoxia causes sediment to release phosphorus and prevents animals from colonizing seafloor habitats. Accordingly, we propose that the animals were preserved during brief episodes of bottom water oxia and/or dysoxia, when the environment would have been most favorable to benthic communities and phosphate mineralization. In this setting, phosphatization may have been fueled by phosphate delivery from continental weathering in response to climatic warming, ocean upwelling of eutrophic water, and/or nutrient trapping by anoxia in the basin.