Early Cretaceous angiosperm pollen from a low-latitude succession (Araripe Basin, NE Brazil)

Abstract

The radiation of flowering plants during the Cretaceous represents a marked evolutionary turnover from gymnosperm- to angiosperm-dominated ecosystems within a time span of about 30 Ma. Despite the importance of this profound ecological transformation, many aspects regarding the timing, floral composition and spatial distribution of early angiosperms are poorly documented. Here, we present a record of early angiosperm pollen from the Brazilian Araripe Basin from the late Aptian to early Albian time interval. For this study, 17 samples from 5 sedimentary sections, spanning a total of ∼ 150 m, have been investigated for their palynological content with particular attention on the occurrence of angiosperm pollen. Our results show a relatively high angiosperm pollen diversity of 70 different taxa, including numerous undescribed forms. Across the succession, angiosperm pollen accounts on average for 7% of the total palynoflora, with maximum abundances reaching 18%. Dominant taxa include monocolpate pollen of “magnoliid” or monocotyledon origin (e.g. Stellatopollis, Retimonocolpites, Pennipollis, Dichastopollenites, and Trisectoris) as well as pollen with eudicotyledon affinities (e.g. triaperturate forms like Rousea, Tricolpites, and Striatopollis). Judging from the existing evidence it appears that the diversity of the late Aptian–early Albian angiosperm palynoflora from the Araripe Basin has been underestimated. In addition, the composition of the total palynoflora shows congruent shifts in the abundance of hygrophilic ferns, Afropollis spp. and angiosperm pollen. The co-occurrence of moisture-loving ferns and early angiosperm pollen may support the hypothesis that early angiosperms evolved and diversified in moist and shady disturbed habitats near the palaeoequator.