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The evolution of neotropical mangroves has not been a constant and gradual enrichment trend, but a complex process in which more stable phases have alternated with others of intense speciation, strong reductions in geographic ranges, and even mass extinctions. The present is a review of the changes occurred on neotropical mangroves in the Eocene/Oligocene boundary (EO), when they suffered their major evolutionary revolution. The purpose is to illustrate the change and discuss its possible causes.

The EO boundary is known to be the largest mass extinction event of the Tertiary, affecting a wide range of marine and terrestrial taxa. Climate is the more likely cause for this extinction event. Indeed, a significant fraction of the Eocene biota, adapted to warm and humid conditions, perished in the Late Eocene, when the climate became cold and arid. The new taxa which appeared from the Oligocene led to the present-day biota. In northern South America, the terrestrial flora experienced a turnover of about 50%. The neotropical mangroves radically changed in their composition. The eocene mangroves were dominated by Pelliciera Nypa, Acrostichum and an unknown taxon represented by the fossil pollen Brevitricolpites variabilis. The only survivor at present-day is Acrostichum, since B, variabilis disappeared at the end of the Eocene, whereas Nypa and Pelliciera notably reduced their ranges of distribution to relictual areas in the Indomalesian region (Nypa) and Central America (Pelliciera). The most accepted causes for this change are the environmental changes occurred at the end of the Eocene (glaciations, aridity and sea-level drops). The post-Eocene mangroves were fully established in the Miocene, when an important increase in the Rhizophora pollen (which was already present, but in very low quantities, in the Late Eocene) has been recorded. No more extinctions occurred from the Oligocene, when a diversification process started. The nowadays common elements progressively appeared in the Miocene (Avicennia), Pliocene (Laguncularia) and Quaternary (Conocarpus). The increase in biodiversity was slow in the Oligocene and Miocene, faster in the Pliocene, and especially intense in the Quaternary. Therefore, the present-day taxonomic richness of neotropical mangroves has been reached during the last 1.5 million years.