Studies in Neotropical paleobotany. XII. A palynoflorafrom the Pliocene Rio Banano Formation of Costa Rica and the Neogenevegetation of Mesoamerica.

An assemblage of 17 identified and four unknown pollen and sporetypes is reported from the Pliocene Rio Banano Formation of southeasternCosta Rica. The most abundant are monolete fern spores, Palmae, cf.Antrophyum, Symphonia, Pelliceria,Lacmella (previously unreported in the fossil record),Alchornea, and Sabicea. These arrange into twopaleocommunities-mangroves and lowland tropical rain forest. Annual precipitation is estimated at near the present ∼3500 mm, butless seasonal, and the MAT (mean annual temperature) at ∼27°C. No pollen taxa representing distinctly arid or high-altitude vegetationwas being blown or washed into the coastal depositional basin, and nopollen grains were recovered of northern temperate elements that arepresent in Neogene floras to the north in Guatemala and southeasternMexico. These data are consistent with those from 12 other Miocene andPliocene palynofloras from northern Latin America, indicating the lateappearance of dry habitats and moderate paleoelevations and aprogressive southward introduction of northern temperate elements withlate Cenozoic cooling.