MAASTRICHTIAN TO EARLY MIOCENE PATTERNS OF PLANT DIVERSIFICATION IN THE NEOTROPICS

The Neotropics holds one the highest plant diversities in the world. How this large biodiversity was produced is still uncertain. Many processes and mechanisms that could produce a high biodiversity in the tropics have been proposed in the last decade. In contrast, the patterns of diversification of Neotropical floras through geological time have been little studied. These patterns could be used to test the processes and mechanisms proposed. Here, we studied the pollen and spore diversity record of Colombia and Western Venezuela from the Maastrichtian to the Early Miocene. Thirty-two sections (including outcrops and wells), 4800 samples, and more than 960,000 individual records of pollen and spores were analyzed. Several techniques, including range-through method, detrended correspondence analysis, and Shannon index were used to assess the significance of the observed diversity pattern. The record shows a moderately diverse flora dominated by angiosperms, ferns and gymnosperms during the Maastrichtian, followed by a diversity crisis at the Cretaceous-Tertiary boundary. Paleocene floras have a low diversity and are dominated by angiosperms. Diversity significantly increases at the early to middle Eocene reaching levels similar to modern Neotropical lowland humid forests. This increase in the diversification engine could be related to the Eocene thermal maximum. The extinction rate increases by the end of the Eocene. During the Oligocene and early Miocene there is a period of low background origination and extinction never again reaching the levels seen in the Eocene. The overall pattern shows that plant diversity in the Neotropics is subject to historical accidents that produced discrete pulses of origination and extinction rather than a constant high rate of origination or low rate of extinction. Processes that explain the high diversity in the tropics must take into account this fact.