The Origin of the Modern Amazon Rainforest: Implications of the Palynological and Palaeobotanical Record

Abstract

Northern South America harbours a highly diversifi ed forest vegetation. However, it is not clear when this remarkable diversity was attained and how it was produced. Is the high diversity the product of a positive speciation-extinction balance that accumulated species over long time periods, or is it the product of high origination rates over short time periods, or both? Middle Cretaceous fl oras, although very poorly studied, are dominated by non-angiosperm taxa. By the Paleocene, pollen and macrobotanical fossils suggest that the basic phylogenetic composition and fl oral physiognomy of Neotropical rainforests were already present. Hence there was a profound change in Amazonian fl ora during the Late Cretaceous, that still needs to be documented. Levels of Paleocene diversity are much lower than those of modern tropical rainforests. By the Early Eocene, however, pollen diversity was very high, exceeding values of modern rainforests. At the EoceneOligocene a major drop in diversity coincided with an episode of global cooling. The palynological and palaeobotanical records of Amazonia suggest that high levels of diversity existed during the Miocene, a period when the boundary conditions for sustaining a rainforest (e.g. low seasonality, high precipitation, edaphic heterogeneous substrate) were met. The predecessor of the present rainforest was formed during the Paleogene and Neogene when the western Amazon lowlands were affected by Andean tectonism, which radically changed drainage systems and promoted wetland development. An overall global cooling during the Neogene also may have affected the rainforest, decreasing its area and expanding adjacent savanna belts. Recent events like the Quaternary ice ages also played a role in the forest dynamics and composition, although it seems to have been minor. In this chapter we will review the main characteristics of the Neogene palynological and palaeobotanical records in Amazonia, and we will make some comparisons with pre-and post-Neogene records. The data indicate that the Amazonian rainforest is more likely to be a product of a dynamic geological history stretching back over the past 25 million years rather than the last few hundred thousand years.

Indicators of Holocene sea level changes along the coast of the states of Pernambuco and Paraíba, Brazil

“…Diatoms are excellent indicators of former sea levels in Quaternary studies worldwide (Horton and Sawai, 2010) and its use in association with pollen and spore grains have been employed by Castro et al (2013) to determine Quaternary sea level changes in Amazonian coast and by Amaral et al (2012) for southern Brazil whereas pollen, as the principal proxy, in studies of alternating sea level fluctuations are reported by Haberle (1997) in the Amazon and by Behling et al (2000) in northeastern Brazil. A more complete use of various microfossils, including pollen, spores, foraminifera and algal remains in reconstitution of paleoenvironments under the context of sea level change, is given by Jaramillo et al (2010). These studies exemplify the generalized use of such microfossils as reliable proxies for the evaluation of past changes in former sea levels in Quaternary and Cenozoic studies.…”

Crocodylian diversity peak and extinction in the late Cenozoic of the northern Neotropics

“…Palaeoenvironmental reconstructions based on palynofloras from the Urumaco Formation suggest a continuation of the Amazonian forest into northwestern Venezuela during the Miocene 39 , with the faunal context including marginal marine, freshwater and continental vertebrates 40 . The latest Mioceneearly Pliocene Codore Formation flora replaced the Amazonian palynoflora with xerophyte-dominated vegetations during the major environmental change related to the collapse of the Urumaco delta in the late Miocene, which correlates with a major uplift of the northern Andes 41 and the eastward changing hydrograph course of a paleo-Orinoco River 10,42 .…”

Multilocus Species Trees Show the Recent Adaptive Radiation of the Mimetic Heliconius Butterflies

“…Bayesian modeling shows that the gains have been gradual and cannot be correlated with a single environmental factor, although the speciation of Heliconius and Eueides may have been stimulated by the second rapid stage of Andean orogeny approximately 12 Ma (Rull 2011), which strongly changed the elevation gradients in the Central and Eastern sectors (Gregory-Wodzicki 2000; Blandin and Purser 2013). This was contemporaneous with climatic changes that affected the distribution of the rainforest (Lewis et al 2007;Jaramillo et al 2010), and followed shortly by the entrenchment of a major barrier, the Amazon, in its modern course 10 Ma (Hall and Harvey 2002;Hoorn et al 2010). Nonetheless, our results do not strongly support such a correlation and highlight the dangers (Rabosky 2014) of the commonly used approach of selecting a single rate shift configuration (reviewed in Stadler 2013 example, analysis of the Heliconiini data with DDD provided false confidence in a single distinct shift to a much higher rate of diversification.…”