Neogene History of the Amazonian Flora: A Perspective Based on Geological, Palynological, and Molecular Phylogenetic Data

The Amazon hosts one of the largest and richest rainforests in the world, but its origins remain debated. Growing evidence suggests that geodiversity and geological history played essential roles in shaping the Amazonian flora. Here we summarize the geo-climatic history of the Amazon and review paleopalynological records and time-calibrated phylogenies to evaluate the response of plants to environmental change. The Neogene fossil record suggests major sequential changes in plant composition and an overall decline in diversity. Phylogenies of eight Amazonian plant clades paint a mixed picture, with the diversification of most groups best explained by constant speciation rates through time, while others indicate clade-specific increases or decreases correlated with climatic cooling or increasing Andean elevation. Overall, the Amazon forest seems to represent a museum of diversity with a high potential for biological diversification through time. To fully understand how the Amazon got its modern biodiversity, further multidisciplinary studies conducted within a multimillion-year perspective are needed. ▪The history of the Amazon rainforest goes back to the beginning of the Cenozoic (66 Ma) and was driven by climate and geological forces. ▪In the early Neogene (23-13.8 Ma), a large wetland developed with episodic estuarine conditions and vegetation ranging from mangroves to terra firme forest. ▪In the late Neogene (13.8-2.6 Ma), the Amazon changed into a fluvial landscape with a less diverse and more open forest, although the details of this transition remain to be resolved. ▪These geo-climatic changes have left imprints on the modern Amazonian diversity that can be recovered with dated phylogenetic trees. ▪Amazonian plant groups show distinct responses to environmental changes, suggesting that Amazonia is both a refuge and a cradle of biodiversity

Reconciling the Cretaceous breakup and demise of the Phoenix Plate with East Gondwana orogenesis in New Zealand

Following hundreds of millions of years of subduction in all circum-Pacific margins, the Pacific Plate started to share a mid-ocean ridge connection with continental Antarctica during a Late Cretaceous south Pacific plate reorganization. This reorganization was associated with the cessation of subduction of the remnants of the Phoenix Plate along the Zealandia margin of East Gondwana, but estimates for the age of this cessation from global plate reconstructions (∼86 Ma) are significantly younger than those based on overriding plate geological records (105–100 Ma). To find where this discrepancy comes from, we first evaluate whether incorporating the latest available marine magnetic anomaly interpretations change the plate kinematic estimate for the end of convergence. We then identify ways to reconcile the outcome of the reconstruction with geological records of subduction along the Gondwana margin of New Zealand and New Caledonia. We focus on the plate kinematic evolution of the Phoenix Plate from 150 Ma onward, from its original spreading relative to the Pacific Plate, through its break-up during emplacement of the Ontong Java Nui Large Igneous Province into four plates (Manihiki, Hikurangi, Chasca, and Aluk), through to the end of their subduction below East Gondwana, to today. Our updated reconstruction is in line with previous compilations in demonstrating that as much as 800–1100 km of convergence occurred between the Pacific Plate and Zealandia after 100 Ma, which was accommodated until 90–85 Ma. Even more convergence occurred at the New Zealand sector owing to spreading of the Hikurangi Plate relative to the Pacific Plate at the Osbourn Trough, with the most recent age constraints suggesting that spreading may have continued until 79 Ma. The end of subduction below most of East Gondwana coincides with a change in relative plate motion between the Pacific Plate and East Gondwana from westerly to northerly, of which the cause remains unknown. In addition, the arrival of the Hikurangi Plateau in the subduction zone occurred independent from, and did not likely cause, the change in Pacific Plate motion. Finally, our plate reconstruction suggests that the previously identified geochemical change in the New Zealand arc around 105–100 Ma that was considered evidence of subduction cessation, may have been caused by Aluk-Hikurangi ridge subduction instead. The final stages of convergence before subduction cessation must have been accommodated by subduction without or with less accretion. This is common in oceanic subduction zones but makes dating the cessation of subduction from geological records alone challenging

Freshwater fish diversity in the western Amazon basin shaped by Andean uplift since the Late Cretaceous

South America is home to the highest freshwater fish biodiversity on Earth, and the hotspot of species richness is located in the western Amazon basin. The location of this hotspot is enigmatic, as it is inconsistent with the pattern observed in river systems across the world of increasing species richness towards a river’s mouth. Here we investigate the role of river capture events caused by Andean mountain building and repeated episodes of flooding in western Amazonia in shaping the modern-day richness pattern of freshwater fishes in South America, and in Amazonia in particular. To this end, we combine a reconstruction of river networks since 80 Ma with a mechanistic model simulating dispersal, allopatric speciation and extinction over the dynamic landscape of rivers and lakes. We show that Andean mountain building and consequent numerous small river capture events in western Amazonia caused freshwater habitats to be highly dynamic, leading to high diversification rates and exceptional richness. The history of marine incursions and lakes, including the Miocene Pebas mega-wetland system in western Amazonia, played a secondary role

A global apparent polar wander path for the last 320 Ma calculated from site-level paleomagnetic data

Apparent polar wander paths (APWPs) calculated from paleomagnetic data describe the motion of tectonic plates relative to the Earth's rotation axis through geological time, providing a quantitative paleogeographic framework for studying the evolution of Earth's interior, surface, and atmosphere. Previous APWPs were typically calculated from collections of paleomagnetic poles, with each pole computed from collections of paleomagnetic sites, and each site representing a spot reading of the paleomagnetic field. It was recently shown that the choice of how sites are distributed over poles strongly determines the confidence region around APWPs and possibly the APWP itself, and that the number of paleomagnetic data used to compute a single paleomagnetic pole varies widely and is essentially arbitrary. Here, we use a recently proposed method to overcome this problem and provide a new global APWP for the last 320 million years that is calculated from simulated site-level paleomagnetic data instead of from paleopoles, in which spatial and temporal uncertainties of the original datasets are incorporated. We provide an updated global paleomagnetic database scrutinized against quantitative, stringent quality criteria, and use an updated global plate motion model. The new global APWP follows the same trend as the most recent pole-based APWP but has smaller uncertainties. This demonstrates that the first-order geometry of the global APWP is robust and reproducible. Moreover, we find that previously identified peaks in APW rate disappear when calculating the APWP from site-level data and correcting for a temporal bias in the underlying data. Finally, we show that a higher-resolution global APWP frame may be determined for time intervals with high data density, but that this is not yet feasible for the entire 320–0 Ma time span. Calculating polar wander from site-level data provides opportunities to significantly improve the quality and resolution of the global APWP by collecting large and well-dated paleomagnetic datasets from stable plate interiors, which may contribute to solving detailed Earth scientific problems that rely on a paleomagnetic reference frame

On the enigmatic birth of the Pacific Plate within the Panthalassa Ocean

The oceanic Pacific Plate started forming in Early Jurassic time within the vast Panthalassa Ocean that surrounded the supercontinent Pangea, and contains the oldest lithosphere that can directly constrain the geodynamic history of the circum-Pangean Earth. We show that the geometry of the oldest marine magnetic anomalies of the Pacific Plate attests to a unique plate kinematic event that sparked the plate’s birth at virtually a point location, surrounded by the Izanagi, Farallon, and Phoenix Plates. We reconstruct the unstable triple junction that caused the plate reorganization, which led to the birth of the Pacific Plate, and present a model of the plate tectonic configuration that preconditioned this event. We show that a stable but migrating triple junction involving the gradual cessation of intraoceanic Panthalassa subduction culminated in the formation of an unstable transform-transform-transform triple junction. The consequent plate boundary reorganization resulted in the formation of a stable triangular three-ridge system from which the nascent Pacific Plate expanded. We link the birth of the Pacific Plate to the regional termination of intra-Panthalassa subduction. Remnants thereof have been identified in the deep lower mantle of which the locations may provide paleolongitudinal control on the absolute location of the early Pacific Plate. Our results constitute an essential step in unraveling the plate tectonic evolution of “Thalassa Incognita” that comprises the comprehensive Panthalassa Ocean surrounding Pangea

Reconstructing Jurassic‐Cretaceous Intra‐Oceanic Subduction Evolution in the Northwestern Panthalassa Ocean Using Ocean Plate Stratigraphy From Hokkaido, Japan

Plate reconstructions of the Panthalassa Ocean typically portray a simple system of diverging plates surrounded by active margins, yet geological and seismic tomographic records demonstrate that intra-oceanic subduction existed. Here, we reconstruct the plate tectonic evolution of the pre-Cretaceous intra-oceanic Oku-Niikappu island arc, remnants of which are exposed on Hokkaido, Japan. This arc formed at a Jurassic subduction zone separating two oceanic plates: the Izanagi Plate and the here proposed ‘Izanami’ Plate. The Oku-Niikappu arc was previously shown to have gone extinct in an intra-oceanic setting, was subsequently (hyper)extended, and overlain by Berriasian cherts. The extinct arc remained on the Panthalassa ocean floor for ∼45 Myr until its ∼100 Ma accretion to Hokkaido, revealing an original position far from the continental margin and likely above the previously identified Telkhinia slabs. We show that arc extinction coincided with a northwestern Panthalassa plate reorganization recorded by a ∼30° change in spreading direction, and that extinction and subsequent extension of the arc is straightforwardly explained by subduction of the Izanami-Pacific ridge followed by continued divergence between the Izanagi and Pacific plates. From our reconstruction, it follows that the outer zone of Japan, to which the accretionary complex in which the Oku-Niikappu Complex resides belongs, was separated from the inner zone by a back-arc basin during the Early to mid-Cretaceous. This study illustrates the value of accretionary orogens in the development of plate reconstructions of lost oceanic plates and ancient continental margins, particularly when combined with seismic tomographic and marine geophysical data sets

Neogene History of the Amazonian Flora: A Perspective Based on Geological, Palynological, and Molecular Phylogenetic Data

International audienceThe Amazon hosts one of the largest and richest rainforests in the world, but its origins remain debated. Growing evidence suggests that geodiversity and geological history played essential roles in shaping the Amazonian flora. Here we summarize the geo-climatic history of the Amazon and review paleopalynological records and time-calibrated phylogenies to evaluate the response of plants to environmental change. The Neogene fossil record suggests major sequential changes in plant composition and an overall decline in diversity. Phylogenies of eight Amazonian plant clades paint a mixed picture, with the diversification of most groups best explained by constant speciation rates through time, while others indicate clade-specific increases or decreases correlated with climatic cooling or increasing Andean elevation. Overall, the Amazon forest seems to represent a museum of diversity with a high potential for biological diversification through time. To fully understand how the Amazon got its modern biodiversity, further multidisciplinary studies conducted within a multimillion-year perspective are needed. ▪ The history of the Amazon rainforest goes back to the beginning of the Cenozoic (66 Ma) and was driven by climate and geological forces. ▪ In the early Neogene (23–13.8 Ma), a large wetland developed with episodic estuarine conditions and vegetation ranging from mangroves to terra firme forest. ▪ In the late Neogene (13.8–2.6 Ma), the Amazon changed into a fluvial landscape with a less diverse and more open forest, although the details of this transition remain to be resolved. ▪ These geo-climatic changes have left imprints on the modern Amazonian diversity that can be recovered with dated phylogenetic trees. ▪ Amazonian plant groups show distinct responses to environmental changes, suggesting that Amazonia is both a refuge and a cradle of biodiversity

The Miocene wetland of western Amazonia and its role in Neotropical biogeography

In the Miocene (23-5 Ma), a large wetland known as the Pebas System characterized western Amazonia. During the Middle Miocene Climatic Optimum (c. 17-15 Ma), this system reached its maximum extent and was episodically connected to the Caribbean Sea, while receiving sediment input from the Andes in the west, and the craton (continental core) in the east. Towards the late Miocene (c. 10 Ma) the wetland transitioned into a fluvial-dominated system. In biogeographic models, the Pebas System is often considered in two contexts: one describing the system as a cradle of speciation for aquatic or semi-aquatic taxa such as reptiles, molluscs and ostracods, and the other describing the system as a barrier for dispersal and gene flow for amphibians and terrestrial taxa such as plants, insects and mammals. Here we highlight a third scenario in which the Pebas System is a permeable biogeographical system. This model is inspired by the geological record of the mid-Miocene wetland, which indicates that sediment deposition was cyclic and controlled by orbital forcing and sea-level change, with environmental conditions repeatedly altered. This dynamic landscape favoured biotic exchange at the interface of (1) aquatic and terrestrial, (2) brackish and freshwater and (3) eutrophic to oligotrophic conditions. In addition, the intermittent connections between western Amazonia and the Caribbean Sea, the Andes and eastern Amazonia favoured two-way migrations. Therefore, biotic exchange and adaptation was probably the norm, not the exception, in the Pebas System. The myriad of environmental conditions contributed to the Miocene Amazonian wetland system being one of the most species-rich systems in geological history.ISSN:0024-4074ISSN:1095-833

Elevational Goldilocks zone underlies the exceptional diversity of a large lizard radiation (Liolaemus; Liolaemidae)

Mountains are among the most biodiverse regions on the planet, and how these landforms shape diversification through the interaction of biological traits and geo-climatic dynamics is integral to understanding global biodiversity. In this study, we investigate the dual roles of climate change and mountain uplift on the evolution of a hyper-diverse radiation, Liolaemus lizards, with a spatially explicit model of diversification using a reconstruction of uplift and paleotemperature in central and southern South America. The diversification model captures a hotspot for Liolaemus around 40°S in lineages with low-dispersal ability and narrow niche breadths. Under the model, speciation rates are highest in low latitudes (\u3c35°S) and mid elevations (~1,000 m), while extinction rates are highest at higher latitudes (\u3e35°S) and higher elevations (\u3e2,000 m). Temperature change through the Cenozoic explained variation in speciation and extinction rates through time and across different elevational bands. Our results point to the conditions of mid elevations being optimal for diversification (i.e., Goldilocks Zone), driven by the combination of (1) a complex topography that facilitates speciation during periods of climatic change, and (2) a relatively moderate climate that enables the persistence of ectothermic lineages and buffers species from extinction