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What was the composition of the Cretaceous neotropical floras? When and how did tropical rain forests first appear? In this work  we address these questions by investigating the palynological content of several surface/subsurface sections from Colombia, ranging in age from Middle Aptian to Late Maastrichtian. During the Aptian – Albian interval the neotropical flora was clearly dominated by spores, with common gymnosperms, while angiosperm and gnetales were present in low abundances. In terms of diversity, of the 113 species we found, 51 were spores, 36 flowering plants, 14 gymnosperms and 12 gnetales. In contrast, Cenomanian assemblages gave rise to forests with abundant and diverse elements with affinity to gnetales, a well diversified but relatively low abundant assemblage of angiosperms –characterized by little evolved apertures-, spores and common gymnosperms. The Cenomanian-Turonian marks a turnover in Neotropical floras, with Turonian flowering plants found in high diversities and abundances, while gnetalean abundance and diversity decreased severely compared to Albian and Cenomanian times. Coniacian/Campanian rocks show a very important marine influence and floral diversity artificially decreases due to high sea-levels. At this time dinoflagellates are very diverse and correspond with tropical provinces previously reported for the Tethyan Ocean. Late Campanian-Maastrichtian microfloras are differentiated from Cenomanian assemblages in that pteridophyte spores and angiosperm pollen became dominant, while gnetalean-like pollen and other gymnosperms are present only as subordinate elements. Finally the Cretaceous-Tertiary boundary corresponds with an episode of increasing extinction of angiosperms and pteridophytes, and the presence of presumably poorly stratified forests. Our results agree with phylogenetic studies that indicate a middle-Cretaceous age for the radiation of many angiosperms clades. Nevertheless, our findings imply that angiosperms did not dominate the landscape long time after they first appear, but most probably conformed poorly stratified forests that contrast with the structure of today’s tropical rain forests.

Cretaceous biostratigraphy, Northwestern South America, angiosperms, gymnosperms, gnetales, dinoflagellates