Two distinct and short-lived flooding events of shallow marine waters covered western Amazonia during the Miocene.

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.

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Taxonomic resolution is a major challenge in palynology, largely limiting the ecological and evolutionary interpretations possible with deep-time fossil pollen data. We present an approach for fossil pollen analysis that uses optical superresolution microscopy and machine learning to create a quantitative and higher throughput workflow for producing palynological identifications and hypotheses of biological affinity. We developed three convolutional neural network (CNN) classification models: maximum projection (MPM), multislice (MSM), and fused (FM). We trained the models on the pollen of 16 genera of the legume tribe Amherstieae, and then used these models to constrain the biological classifications of 48 fossil Striatopollis specimens from the Paleocene, Eocene, and Miocene of western Africa and northern South America. All models achieved average accuracies of 83 to 90% in the classification of the extant genera, and the majority of fossil identifications (86%) showed consensus among at least two of the three models. Our fossil identifications support the paleobiogeographic hypothesis that Amherstieae originated in Paleocene Africa and dispersed to South America during the Paleocene-Eocene Thermal Maximum (56 Ma). They also raise the possibility that at least three Amherstieae genera (Crudia, Berlinia, and Anthonotha) may have diverged earlier in the Cenozoic than predicted by molecular phylogenies.

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During the Miocene, Andean tectonism caused the development of a vast wetland across western Amazonia. Palynological studies have been the main source of chronological and paleobotanical information for this region, including several boreholes in the Solimões Formation in western Brazilian Amazonia. Here, a palynological study of well core 1-AS-105-AM drilled in Tabatinga (Amazonas, Brazil) is presented: 91 new taxa are erected (25 spores and 66 pollen, including one new genus), 16 new combinations are proposed, and a list of botanical/ecological affinities is updated. We recorded 23,880 palynomorphs distributed in 401 different types. Among pollen and spores, 62 extant families and 99 extant genera were identified, which accounts for 39% and 30% of known botanical affinities to the family and genus level, respectively. Individual samples have pollen/spore counts with approximately 25% to 95% of known affinities to the family level. Pollen associations are sourced primarily from the wetland environments and to a minor extent from nonflooded forests. Palynological diversity analyses indicate an increase from the early to the middle/early late Miocene in core 1-AS-105-AM. Probable scenarios to explain this diversity increase include a higher degree of environmental complexity from the middle Miocene onwards, that is, a more heterogeneous riverscape, including broader extensions of nonflooded forests, as opposed to the swamp-dominated early Miocene. Additionally, the positive effects of the Miocene Climatic Optimum on plant richness could explain the increase in pollen richness. We posit hypotheses of forest diversification that can be tested as more botanical affinities are established along with a longer Miocene record.

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