Palynological record of the Cretaceous angiosperm radiation: Diversity, abundance and morphological patterns

During the Cretaceous, terrestrial ecosystems began to undergo a dramatic reorganization as angiosperms (flowering plants) radiated taxonomically, ecologically and morphologically. The angiosperm radiation ended the ecological dominance of gymnosperms (conifers, cycads, etc.) and free-sporing plants (ferns, mosses, etc.) in many terrestrial habitats. To examine the angiosperm radiation, I compiled taxonomically-standardized palynological (pollen and spores) data (4,400 species in 2,500 samples for 47,000 records) from the published literature to examine temporal and spatial patterns in terrestrial vegetation, and morphological innovation among angiosperms in North America across a broad range of paleolatitudes.; On a continental scale, angiosperm species diversity (number of species), floristic diversity (percent of species within a sample) and ecological abundance (percent of specimens within a sample) reveal significant increases through the Cretaceous. Gymnosperms exhibit a more marked decline in ecological abundance than in floristic diversity, while the opposite is true of free-sporing plants. Contrary to previous studies, angiosperms do not attain dominance over gymnosperms and free-sporing plants in most assemblages even by the end of the Cretaceous.; Segregation of samples by paleolatitude reveals underlying structure to the radiation. Higher latitudes lag behind lower latitudes in angiosperm diversity and in the ecological abundance of angiosperms. Further, the lag is sufficiently great that continental abundance curves, combining data across latitudes, obscures decreases in abundance at smaller spatial scales. Quantitatively-defined palynological provinces suggest the presence of distinct floral regions as early as the Aptian rather than just in the Late Cretaceous as previously documented. These results imply that angiosperms were sorting along established, presumably climatic, gradients and that they did not substantially affect the overall distributional patterns of vegetation assemblages.; Taxonomic data, useful for the analysis of diversity patterns, does not capture key details of morphological variety among clades. Morphological variety, measured as disparity between taxa, shows that angiosperms rapidly increase in disparity in the Aptian and that disparity remains nearly constant throughout the rest of the Cretaceous. This pattern of immediate high morphological disparity contrasts with the more gradual accumulation of species diversity and suggests changes in evolutionary stepsizes over time.