The stepwise rise of angiosperm-dominated terrestrial ecosystems.

Angiosperms are the most diverse and abundant plant taxon today and dominate the majority of Earth's terrestrial ecosystems. They underwent rapid divergence and biogeographic expansion from the early to the middle Cretaceous. Yet, transformative ecosystem change brought about by the increased ecological dominance of angiosperms unfolded progressively until the Late Cretaceous. After the Cretaceous-Paleogene (K-Pg) boundary, angiosperms restructured terrestrial ecosystems towards a modern form. By the Neogene, crown groups that make up modern terrestrial angiosperm biodiversity radiated, and regional floristic distinctions were established concurrently with the steepened latitudinal and vertical temperature gradients. Here, we summarize, based on fossils and molecular evidence, when and how angiosperms came to diversify, dominate, and shape terrestrial ecosystems, leading to the emergence and spread of angiosperm-dominated floras. We highlight five major phases of angiosperm evolution that took place against a background of palaeogeography and climate changes. There is a consistent delay in ecological dominance after lineage origination and taxonomic diversification, as a result of which angiosperms did not achieve ecological dominance across terrestrial biomes in a single step. The patterns of diversity seen among extant angiosperms, the dominant angiosperm groups within modern ecosystems, and the restriction of different groups of angiosperms to different parts of the world, reflect the contingent nature of the process of lineage diversification in the context of long-term, substantial and ongoing environmental change. Determining the origins, diversification, and ecological dominance of angiosperms continues to be a challenge and requires elucidation of their early forms, functions, habitats, and environmental interactions throughout evolutionary history.