Sporopollenin chemistry and its durability in the geological record: an integration of extant and fossil chemical data across the seed plants.

Sporopollenin is a highly resistant biopolymer that forms the outer wall of pollen and spores (sporomorphs). Recent research into sporopollenin chemistry has opened up a range of new avenues for palynological research, including chemotaxonomic classification of morphologically cryptic taxa. However, there have been limited attempts to directly integrate extant and fossil sporopollenin chemical data. Of particular importance is the impact of sample processing to isolate sporopollenin from fresh sporomorphs, and the extent of chemical changes that occur once sporomorphs enter the geological record. Here, we explore these issues using Fourier transform infrared (FTIR) microspectroscopy data from extant and fossil grass, Nitraria (a steppe plant), and conifer pollen. We show a 98% classification success rate at subfamily level with extant grass pollen, demonstrating a strong taxonomic signature in isolated sporopollenin. However, we also reveal substantial chemical differences between extant and fossil sporopollenin, which can be tied to both early diagenetic changes acting on the sporomorphs and chemical derivates of sample processing. Our results demonstrate that directly integrating extant and late Quaternary chemical data should be tractable as long as comparable sample processing routines are maintained. Consistent differences between extant and deeper time sporomorphs, however, suggests that classifying fossil specimens using extant training sets will be challenging. Further work is therefore required to understand and simulate the effects of diagenetic processes on sporopollenin chemistry

Linking modern-day relicts to a Miocene mangrove community of western Amazonia

The Amazon drainage basin is extremely biodiverse, yet the origins of this diversification remain much debated. One of the possible drivers of plant diversity are the marine incursions that reached Amazonia during the Miocene and connected western Amazonia with the Caribbean. In the Miocene, large parts of western Amazonia were covered by extensive wetlands that, during high eustatic episodes, were episodically colonised by coastal taxa such as mangroves. In this paper, we hypothesise that some of these mangrove community taxa could adapt to freshwater conditions enriching the modern plant composition of the Amazon drainage basin. To assess the past plant composition in the basin, we statistically analyse the palynological composition of two Miocene sections from western Amazonia that were especially rich in presumed mangrove pollen (Zonocostites ramonae). We identify the pollen taxa that coexisted with this community using clustering methods supported by Kendall’s W coefficient concordance analysis. Our results suggest that at least fourteen taxa are closely associated with Zonocostites ramonae (Cricotriporites guianensis, Deltoidospora adriennis, Psilabrevitricolporites devriesii, Psiladiporites redundantis, Psilamonocolpites amazonicus, P. rinconii, Psilatricolporites crassoexinatus, P. labiatus, P. operculatus, Psilatriporites corstanjei, Retitricolporites kaarsii, Rhoipites guianensis, Rhoipites hispidus, and Tetracolporopollenites transversalis). We also illustrate the pollen of this fossil mangrove, and some of its associated fossil taxa, using light microscopy (LM) and scanning electron microscopy (SEM), and we compare them with potential nearest living relatives (NLR). We found that pollen of the modern mangrove Rhizophora mangle is the NLR of Zonocostites ramonae. Of the three associated taxa, the best analogy is between Psilabrevitricolporites devriesii and Humiria balsamifera, the latter a taxon best known from the coastal restinga vegetation in Brazil and Surinam. Tentatively, we assign Forsteronia spp. as NLR for Cricotriporites guianensis, and we propose Euterpe sp. for Psilamonocolpites rinconii (but also Oenocarpus, Hyospathe, Prestoea, and Sabinaria are affine). Based on this study we propose that, at least for some fossil taxa of the Miocene mangrove environment, there are still NLR or relict species that occur in inland Amazonia and along the South American coastline. We thus conclude that the Amazonian flora, like riverine fauna such as the pink river dolphin (Inia) and selected fish taxa, carry an imprint of the Miocene coastal communities

Climate and geological change as drivers of Mauritiinae palm biogeography

Aim Forest composition and distribution are determined by a myriad of factors, including climate. As models of tropical rain forest, palms are often used as indicator taxa, particularly the Mauritiinae. We question, what characterizes the Mauritiinae pollen in the global fossil record? And when did the Mauritiinae become endemic to South America?Location Global tropics.Taxon Mauritiinae palms (Arecaceae: Lepidocaryeae).Methods Pollen trait data from extinct and extant Mauritiinae pollen were generated from light-, scanning-, and transmission electron microscopy. Statistical morphometric analysis was used to define species and their relationships to other Mauritiinae. We also compiled a comprehensive pollen database for extinct and extant Mauritiinae and mapped their global geographical distribution from Late Cretaceous to present, using GBIF and fossil data.Results Our morphometric analysis identified 18 species (11 extinct and seven extant), all exhibiting exine indentations, a synapomorphy of the subtribe. The fossil taxa and early divergent extant Lepidocaryum are all monosulcate, whereas the extant Mauritia and Mauritiella species are all monoulcerate. Paleobiogeographical maps of fossil Mauritiinae pollen occurrences suggest the taxon originated in equatorial Africa during the Cretaceous, and expanded their range to South America, and to India in the Paleocene. Range retraction started in the early Eocene with extirpation from India, and reduction in diversity in Africa culminating at the Eocene-Oligocene Transition (EOT). In contrast, in South America, the distribution is maintained, and since the Neogene Mauritiinae palms are mostly restricted to swampy, lowland habitats.Main conclusions Morphometric analysis shows that since their origin Mauritiinae pollen are relatively species poor, and Mauritiidites resembles Lepidocaryum. We also conclude that the biogeographical history of the Mauriitinae and, by extension, tropical forests was strongly affected by global climatic cooling events. In particular, the climate change at the EOT was a fundamental determinant of current tropical forest distribution