The Flower Revolution

The rise of angiosperms was accompanied by massive expansion in biodiversity. From Benton et al., 2021

Angiosperms, or flowering plants, represent almost 90% of all living land plants. The group first appeared in the fossil record during the Early Cretaceous and by the Late Cretaceous, angiosperms came to dominate plant diversity. Charles Darwin’s fascination and frustration with the evolutionary events associated with the origin and early radiation of angiosperms are legendary. On 22 July 1879, in a letter to Joseph Dalton Hooker, Darwin refers to the early evolution of flowering plants as an “abominable mystery”. Since Darwin many new fossils have been found and facilitated the calibration of molecular clock age estimates for various angiosperm clades. Before the Aptian, the only convincing angiosperm megafossils are from the Barremian Las Hoyas flora of Spain and the Yixian flora of northeastern China. By contrast, there is an extensive pre-Aptian pollen record of angiosperms.

Model of the ancestral flower (From Sauquet et al., 2017)

The Angiosperm Terrestrial Revolution (Benton et al., 2021) reshaped the entire terrestrial ecosystem. Flowering plants altered climate and water cycles, and drove a massive expansion in biodiversity of numerous key groups of fungi, insects, arachnids, reptiles, mammals and birds. But angiosperm success lies no only in their possesion of flowers. They have smaller genomes on average than other plants, which lead to small cell sizes in angiosperms with tightly-packed internal structures. Other key innovations like high vein density and densely packed stomata are also related to genome size. Stomata are the controlled pores through which plants exchange gases with their environments, and play a key role in regulating the balance between photosynthetic productivity and water loss through transpiration

Atmospheric CO2 concentrations and paleotemperatures were the major drivers of floristic turnover. Multiple climate proxy records, identified the EECO as the warmest interval of the past 65 million years. During EECO (Eocene Climate Optimum), the warmest interval of the past 65 million years, emerged many angiosperm dominated forest. Today, many organisms depend substantially or entirely on angiosperms for their existence, especially in tropical rain forests. Among them are about 15 000 species of lizards, birds and mammals. 

References:

Benton, Michael J., et al. 2021. The Angiosperm Terrestrial Revolution and the Origins of Modern Biodiversity. New Phytologist. Wiley Online Library https://doi.org/10.1111/nph.17822

Sauquet, H., von Balthazar, M., Magallón, S. et al. The ancestral flower of angiosperms and its early diversification. Nat Commun 8, 16047 (2017). https://doi.org/10.1038/ncomms16047

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