Palynological composition of a Lower Cretaceous South American tropical sequence: Climatic implications and diversity comparisons with other latitudes

American Journal of Botany 99(11): 1819–1827, 2012; http://www.amjbot.org/ © 2012 Botanical Society of America Flowering plants (angiosperms) originated during the Early Cretaceous, approximately 140–135 million years ago (Ma) ( Brenner, 1974 ; Gubeli et al., 1984 ; Hughes and McDougall, 1987 ; Thusu et al., 1988 ), and rapidly diversifi ed and radiated worldwide ( Wang et al., 2009 ; Moore et al., 2010 ). Analyses of Cretaceous palynofl oras by Crane and Lidgard (1989) and Lupia et al. (1999) suggested that angiosperms increased in abundance and diversity through the Early Cretaceous and that by the Late Cretaceous (Cenomanian to Campanian, 99–70 Ma) they were fl oristically dominant in middle and high latitudes of the northern hemisphere. However, the patterns of angiosperm radiation and diversifi cation in low, tropical latitudes are not well understood, mainly because of the few studies from tropical latitudes in Cretaceous successions, compared to the numerous fossil localities studied at higher latitudes (see Crane and Lidgard, 1989 ; Lupia et al., 1999 ). Given the scarcity of plant megafossil records in tropical latitudes, the use of palynology has proven crucial in understanding plant distribution and evolution for this age. Besides, palynological data provides high stratigraphic resolution, as well as large sample sizes, offering the opportunity of analyzing the fossil record using quantitative analytical techniques. The focus of many of the existing tropical palynological studies from the Early Cretaceous has been mainly taxonomic and biostratigraphic, providing mostly qualitative (e.g., presence/absence) or semiquantitative data. While we acknowledge that such qualitative data provide important information about fl oristic assemblages and the initial background for proposing of hypotheses, only quantitative data can be used in more robust statistical analyses, and therefore they are preferred in testing hypotheses and reconstructing fl oristic patterns through time and space (e.g., latitudinal diversity gradients, changes in fl oras due to climatic changes, evolutionary changes). One of the main objectives of this study is to reconstruct the fl oristic composition of a tropical sequence, in Colombia, of 1 Manuscript received 21 March 2012; revision accepted 12 October 2012. This work was supported by funds from the Evolving Earth Foundation, the Colombian Institute of Petroleum—Ecopetrol S.A., the Becker/Dilcher Paleobotany Fund at UF, and a fellowship at the Smithsonian Tropical Research Institute. P.J.M-V is especially thankful to Faculty for the Future, SEAGEP, and the University of Florida Student Research Fellowships; Dr. R. Lupia for kindly providing his compilation of North American palynological data; and T. Lott for obtaining several papers for the literature review. The authors thank M. Carvalho and three anonymous reviewers for comments and suggestions. Any use of trade, product, or fi rm names is for descriptive purposes only and does not imply endorsement by the U. S. Government. 6 Author for correspondence (e-mail: paumejia@ufl .edu)