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Abstract The Cretaceous–Paleogene (K–Pg) mass extinction was geologically instantaneous, causing the most drastic extinction rates in Earth’s History. The rapid species losses and environmental destruction from the Chicxulub impact at 66.02 Ma made the K–Pg the most comparable past event to today’s projected “sixth” mass extinction. The extinction famously eliminated major clades of animals and plankton. However, for land plants, losses primarily occurred among species observed in regional studies but left no global trace at the family or major-clade level, leading to questions about whether there was a significant K–Pg plant extinction. We review emerging paleobotanical data from the Americas and argue that the evidence strongly favors profound (generally >50%), geographically heterogeneous species losses and recovery consistent with mass extinction. The heterogeneity appears to reflect several factors, including distance from the impact site and marine and latitudinal buffering of the impact winter. The ensuing transformations have affected all land life, including true angiosperm dominance in the world’s forests, the birth of the hyperdiverse Neotropical rainforest biome, and evolutionary radiations leading to many crown angiosperm clades. Although the worst outcomes are still preventable, the sixth mass extinction could mirror the K–Pg event by eliminating comparable numbers of plant species in a geologic instant, impoverishing and eventually transforming terrestrial ecosystems while having little effect on global plant-family diversity. 

Leguminosae are one of the most diverse flowering-plant groups today, but the evolutionary history of the family remains obscure because of the scarce early fossil record, particularly from lowland tropics. Here, we report ~500 compression or impression specimens with distinctive legume features collected from the Cerrejón and Bogotá Formations, Middle to Late Paleocene of Colombia. The specimens were segregated into eight fruit and six leaf morphotypes. Two bipinnate leaf morphotypes are confidently placed in the Caesalpinioideae and are the earliest record of this subfamily. Two of the fruit morphotypes are placed in the Detarioideae and Dialioideae. All other fruit and leaf morphotypes show similarities with more than one subfamily or their affinities remain uncertain. The abundant fossil fruits and leaves described here show that Leguminosae was the most important component of the earliest rainforests in northern South America c. 60–58 million years ago. 

The end-Cretaceous event was catastrophic for terrestrial communities worldwide, yet its long-lasting effect on tropical forests remains largely unknown. We quantified plant extinction and ecological change in tropical forests resulting from the end-Cretaceous event using fossil pollen (>50,000 occurrences) and leaves (>6000 specimens) from localities in Colombia. Late Cretaceous (Maastrichtian) rainforests were characterized by an open canopy and diverse plant–insect interactions. Plant diversity declined by 45% at the Cretaceous–Paleogene boundary and did not recover for ~6 million years. Paleocene forests resembled modern Neotropical rainforests, with a closed canopy and multistratal structure dominated by angiosperms. The end-Cretaceous event triggered a long interval of low plant diversity in the Neotropics and the evolutionary assembly of today’s most diverse terrestrial ecosystem.