The biogeography of the araucarian dispersed pollen Cyclusphaera

The pollen genus Cyclusphaera was first described from the Campanian of Peru. The distinctive pollen is spherical to ovoid and disc shaped, with two large openings, resembling pores, opposite each other on the pollen grain. We emend the description of Cyclusphaera scabrata from the Cenozoic of northern South America, based on new data from transmission electron and scanning electron microscopy. The worldwide spatial and temporal distributions of Cyclusphaera are examined. This taxon originated in midlatitudes in the Southern Hemisphere (Gondwana) and subsequently expanded its distribution to higher and lower latitudes, reaching a maximum latitudinal and longitudinal distribution by the middle Cretaceous. Following the Cretaceous, Cyclusphaera was extirpated from middle and high latitudes during the late Cretaceous and Paleogene while increasing its frequency in the tropics during the Cenozoic in both Africa and South America. By the Oligocene, Cyclusphaera was a common element of palynofloras in Colombia and Venezuela. During the Neogene, the distribution in tropical South America became restricted, with the youngest record occurring in the late Miocene of western Colombia. The overall biogeographic pattern of Cyclusphaera is similar to that of Podocarpaceae, one of the most persistent gymnosperm families in the tropics. The extinction of Cyclusphaera could be related to the increase in aridity and expansion of savanna habitats in the northern tropics of South America during the Neogene.