STUDIES IN NEOTROPICAL PALEOBOTANY - XII - A PALYNOFLORA FROM THE PLIOCENE RIO BANANO FORMATION OF COSTA-RICA AND THE NEOGENE VEGETATION OFMESOAMERICA

An assemblage of 17 identified and four unknown pollen and spore types is reported from the Pliocene Rio Banano Formation of southeastern Co sta Rica. The most abundant are monolete fern spores, Palmae, cf. Antr ophyum, Symphonia, Pelliceria, Lacmella (previously unreported in the fossil record), Alchornea, and Sabicea. These arrange into two paleoco mmunities-mangroves and lowland tropical rain forest. Annual precipita tion is estimated at near the present similar to 3500 mm, but less sea sonal, and the MAT (mean annual temperature) at similar to 27 degrees C. No pollen taxa representing distinctly arid or high-altitude vegeta tion was being blown or washed into the coastal depositional basin, an d no pollen grains were recovered of northern temperate elements that are present in Neogene floras to the north in Guatemala and southeaste rn Mexico. These data are consistent with those from 12 other Miocene and Pliocene palynofloras from northern Latin America, indicating the late appearance of dry habitats and moderate paleoelevations and a pro gressive southward introduction of northern temperate elements with la te Cenozoic cooling.