title: Palynological composition of a Lower Cretaceous South American tropical sequence: climatic implications and diversity comparisons with other latitudes.
abstract: OBJECTIVE
  Reconstruction of floristic patterns during the early diversification of angiosperms is impeded by the scarce fossil record, especially in tropical latitudes. Here we collected quantitative palynological data from a stratigraphic sequence in tropical South America to provide floristic and climatic insights into such tropical environments during the Early Cretaceous.
  
  
  METHODS
  We reconstructed the floristic composition of an Aptian-Albian tropical sequence from central Colombia using quantitative palynology (rarefied species richness and abundance) and used it to infer its predominant climatic conditions. Additionally, we compared our results with available quantitative data from three other sequences encompassing 70 floristic assemblages to determine latitudinal diversity patterns.
  
  
  RESULTS
  Abundance of humidity indicators was higher than that of aridity indicators (61% vs. 10%). Additionally, we found an angiosperm latitudinal diversity gradient (LDG) for the Aptian, but not for the Albian, and an inverted LDG of the overall diversity for the Albian. Angiosperm species turnover during the Albian, however, was higher in humid tropics.
  
  
  CONCLUSIONS
  There were humid climates in northwestern South America during the Aptian-Albian interval contrary to the widespread aridity expected for the tropical belt. The Albian inverted overall LDG is produced by a faster increase in per-sample angiosperm and pteridophyte diversity in temperate latitudes. However, humid tropical sequences had higher rates of floristic turnover suggesting a higher degree of morphological variation than in temperate regions.
authors.affiliation: Florida Museum of Natural History and Department of Biology, University of Florida, P.O. Box 117800, Gainesville, Florida 32611-7800, USA. paumejia@ufl .edu
authors.forename: Paula J
authors.initials: PJ
authors.lastname: Mejia-Velasquez
authors.forename: David L
authors.initials: DL
authors.lastname: Dilcher
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Jaramillo
authors.forename: Lucas B
authors.initials: LB
authors.lastname: Fortini
authors.forename: Steven R
authors.initials: SR
authors.lastname: Manchester
mesh_terms: D000704:Analysis of Variance; D044822:Biodiversity; D003105:Colombia; D032462:Cycadopsida / Q000145:classification / Q000254:growth & development*; D005580:Fossils; D005843:Geography; D006813:Humidity; D019684:Magnoliopsida / Q000145:classification / Q000254:growth & development*; D011058:Pollen / Q000254:growth & development*; D013020:South America; D014329:Tropical Climate