Pliocene-Pleistocene Transition Research Articles

Impact of the climatic changes in the Pliocene-Pleistocene transition on Irano-Turanian species. The radiation of genus Jurinea (Compositae)

The Irano-Turanian region is one of the world’s richest floristic regions and the centre of diversity for numerous xerophytic plant lineages. However, we still have limited knowledge on the timing of evolution and biogeographic history of its flora, and potential drivers of diversification remain underexplored. To fill this knowledge gap, we focus on the Eurasian genus Jurinea (ca. 200 species), one of the largest plant radiations that diversified in the region. We applied a macroevolutionary integrative approach to explicitly test diversification hypotheses and investigate the relative roles of geography vs. ecology and niche conservatism vs. niche lability in speciation processes. To do so, we gathered a sample comprising 77% of total genus richness and obtained data about (1) its phylogenetic history, recovering 502 nuclear loci sequences; (2) growth forms; (3) ecological niche, compiling data of 21 variables for more than 2500 occurrences; and (4) paleoclimatic conditions, to estimate climatic stability. Our results revealed that climate was a key factor in the evolutionary dynamics of Jurinea. The main diversification and biogeographic events that occurred during past climate changes, which led to colder and drier conditions, are the following: (1) the origin of the genus (10.7 Ma); (2) long-distance dispersals from the Iranian Plateau to adjacent regions (∼7–4 Ma); and (3) the diversification shift during Pliocene-Pleistocene Transition (ca. 3 Ma), when net diversification rate almost doubled. Our results supported the pre-adaptation hypothesis, i.e., the evolutionary success of Jurinea was linked to the retention of the ancestral niche adapted to aridity. Interestingly, the paleoclimatic analyses revealed that in the Iranian Plateau long-term climatic stability favoured old-lineage persistence, resulting in current high species richness of semi-arid and cold adapted clades; whereas moderate climate oscillations stimulated allopatric diversification in the lineages distributed in the Circumboreal region. In contrast, growth form lability and high niche disparity among closely related species in the Central Asian clade suggest adaptive radiation to mountain habitats. In sum, the radiation of Jurinea is the result of both adaptive and non-adaptive processes influenced by climatic, orogenic and ecological factors.

Neogene–Quaternary tectonic, eustatic and climatic events shaped the evolution of a South American treefrog

AbstractAimUnderstanding how past geological and climatic events could have generated intraspecific genetic variation at different temporal and spatial scales in the Neotropics requires a model encompassing distinct ecoregions. Because Anura species have their evolutionary history affected by climate and environmental changing, it is a suitable model to investigate the signatures of Neotropical historical events in species populations. Here we used a treefrog species to test hypotheses associated with tectonic, eustatic and climatic events along with isolation‐by‐environment and isolation‐by‐distance spatial patterns in genetic diversity.TaxonScinax squalirostris (Lutz, 1925), Anura: Hylidae.LocationAtlantic Forest, Cerrado, Chaco, Uruguayan Savanna and Pampas ecoregions in South America.MethodsWe sequenced nuclear and mitochondrial data from 219 individuals of S. squalirostris sampled at 26 locations in South America. We performed statistical phylogeographic analyses and reconstruction of spatiotemporal dispersal dynamics. Ecological niche modelling was conducted to predict spatial changes in environmental suitability from the Last Glacial Maximum to the Holocene and present day.ResultsWe recovered a significant phylogeographic break roughly dated back to the Miocene (~7.6 Ma), coinciding with the retraction of marine incursions in the Paraná basin. Most dispersal events occurred in cooler periods of the Pliocene–Pleistocene transition. The spatial pattern in genetic diversity was not correlated with geographical distance or environmental variables.Main ConclusionsScinax squalirostris had a quasi‐stable distribution through time. Neogene–Quaternary tectonic, eustatic and climatic events drove the demographic history and dispersal dynamics of species, with a phylogeographical break dated to the Miocene coinciding with retractions of marine incursions in the Paraná basin. Lineage dispersal spread from the southern Atlantic Forest and retrieved gene flow signals congruent with the cold periods of the Pliocene and Pleistocene.

What Does the “Elephant-Equus” Event Mean Today? Reflections on Mammal Dispersal Events around the Pliocene-Pleistocene Boundary and the Flexible Ambiguity of Biochronology

The dispersal of primitive elephantines and monodactyl equids in Eurasia has long been regarded as representative of a substantial turnover in mammal faunas, denoting the spread of open environments linked to the onset of cold and dry conditions in the Northern Hemisphere. During the 1980s, this event was named the “Elephant-Equus event” and it was correlated with the Gauss-Matuyama reversal, today corresponding to the Pliocene-Pleistocene transition and the beginning of the Quaternary, dated at ~2.6 Ma. Therefore, the Elephant-Equus event became a concept of prominent biochronological and paleoecological significance, especially in western Europe. Yet, uncertainties surrounding the taxonomy and chronology of early “elephant” and “Equus”, as well as conceptual differences in adopting (or understanding) the Elephant-Equus event as an intercontinental dispersal event or as a stratigraphic datum, engendered ambiguity and debate. Here, we provide a succinct review of the Elephant-Equus event, considering separately the available evidence on the “elephant” and the “Equus”. Elephantines dispersed out of Africa during the Pliocene (Piacenzian). Their earliest calibrated occurrences from eastern Europe date at ~3.2 Ma and they are usually referred to Mammuthus rumanus, although the allocation of several samples to this species is tentative. Available dating constraints for other localities do not resolve whether the dispersal of Mammuthus was synchronous across Eurasia, but this possibility cannot be ruled out. The spread of Mammuthus was part of an intercontinental faunal exchange between Africa and Eurasia that occurred during the Piacenzian, but in this scenario, Mammuthus is quite unique in being the only genus of African origin dispersing to western Eurasia. The arrival of monodactyl equids from North America coincides with the Pliocene-Pleistocene transition, with several occurrences dated or calibrated at ~2.6 Ma and no compelling evidence prior to this age. In Europe, early monodactyl equids are often aligned to Equus livenzovensis, but the material from the type locality of this species is chronologically time-averaged and taxonomically heterogeneous, and western European samples are seldom abundant or informative. Regardless, this does not diminish the biochronological significance of the “Equus event”. Indeed, while the term “Elephant-Equus event” should no longer be used, as the appearance of elephantines in the European fossil record markedly precedes that of monodactyl equids, we endorse the use of the “Equus event” as a valid alternative to refer to the intercontinental dispersal event that characterizes the middle Villafranchian faunal turnover, epitomized by but not limited to monodactyl equids.

Changes in deep Pacific circulation and carbon storage during the Pliocene-Pleistocene transition

The global climate has been gradually cooling over the Cenozoic and is punctuated by the intensification of Northern Hemisphere Glaciation (NHG) from the latest Pliocene to earliest Pleistocene (∼3.1–2.5 millions of years ago, Ma). A decline of atmospheric CO2 is supposed as a prerequisite for the NHG, but the associated carbon-cycle processes remain elusive. Here we combine foraminiferal records of neodymium isotope and boron-calcium ratio, and simulations of an Earth system model, to investigate changes in the water-mass composition and carbonate-ion concentration of the deep Pacific Ocean during the NHG. Our proxy records have revealed a significant expansion of southern-sourced waters with increased respired carbon storage into the deep Pacific during the NHG. These changes may be explained by strengthened deep-water formation and biological-pump efficiency in the Southern Ocean due to Antarctic sea-ice growth, as suggested by our model experiments and evidence from the Sub-Antarctic region. These results provide key clues for quantifying the role of the dissolved inorganic carbon content of deep Pacific waters in modulating atmospheric CO2 during the NHG.

The Pliocene–Pleistocene transition in the subsurface of the Dutch-Belgian border region: insights from borehole Huijbergen

Cross-border correlations of the Pliocene–Pleistocene successions in the southern Netherlands and northernmost Belgium are problematic, because biostratigraphic markers are often lacking. Correlation is further hampered by the poor age constraints of the Belgian Merksplas Formation. To address these issues, sedimentary, mollusc and dinoflagellate cyst analyses are combined to characterise the lithostratigraphic units in the Huijbergen borehole (The Netherlands) and to provide age estimates. Subsequently, the Huijbergen borehole was correlated with nearby boreholes in Essen and Kalmthout (Belgium). The Piacenzian intervals of the Dutch Oosterhout Formation can be correlated with the Belgian Lillo Formation, with the latter’s threefold borehole log signature appearing virtually continuous across the border between both countries. The Dutch Maassluis and Waalre formations are correlated with the shell-bearing lower part and the unfossiliferous higher part of the Merksplas Formation respectively. Although dinocysts are not age-diagnostic for the Maassluis and Waalre formations in borehole Huijbergen, characteristic interglacial marine shells provide a Gelasian age assessment for the Maassluis Formation. By correlation, this age estimate can also be applied to the lower part of the Merksplas Formation, thereby elucidating the Pliocene–Pleistocene transition near the Dutch-Belgian border.

EARLY PLEISTOCENE SEROTINE BAT <i>EPTESICUS PRAEGLACIALIS</i> (VESPERTILIONIDAE, CHIROPTERA) FROM THE TAURIDA CAVE IN CRIMEA

The cranial and mandibular remains of a large serotine bat Eptesicus praeglacialis Kormos, 1930 are described from the Lower Pleistocene deposits of the Taurida cave in the central Crimea. This is the first finding of the skull material of E. praeglacialis and the first record of the species in Crimea. Judging by the tooth wear stages, the remains of both young and adult specimens are present in the taphocenosis. The small mammal tooth marks on the bones (caused by eating the remnants of soft tissues) in the absence of signs of digestion, characterizing materials from the predatory bird pellets, indicate that the taphocenosis includes the remains of E. praeglacialis individuals that used the cave as a shelter and died there. This corresponds to the idea of appearance of hibernation in caves as a climatically determined ecological adaptation in some European forest-dwelling bats (including Eptesicus) at the Pliocene–Pleistocene transition.

Changing sediment supply during glacial-interglacial intervals in the North Atlantic revealed by particle size characterization and environmental magnetism

The Pliocene-Pleistocene transition is characterized by an abundance of Ice-Rafted Debris (IRD) in the North Atlantic basin. One of the regions affected by IRD during this period is the Gardar Drift, where the DSDP Leg 94 Hole 611A is located. This region received sediments from different sources during the glacial and interglacial intervals (e.g., Iceland and Greenland). We analyzed grain size and particle-size specific magnetic properties of sediments for their provenance characterization between ~2.64 and 2.52 Ma. Our results show that major proportion of bulk sediments during both glacial and interglacial periods were made up of basaltic-rich Icelandic sediments, whereas only during more intense glacial periods (Marine Isotope Stages 100 and 104), a small proportion of non-basaltic sand compositions were identified, possibly sourced from Greenland and other non-basaltic provenances. The non-basaltic sand fractions during the intense glacial periods were likely supplied as IRDs. In addition, a new level of coarse lithics (38 pcs. of >1 mm) composed of different rocks types (e.g., basalt, granite, granodiorite etc.) were identified in DSDP 611A Hole during the end of glacial MIS 104. The coarse lithic fragments showed distinctive magnetic properties than rest of the particle sizes and were classified as Iceberg-Rafted Debris (IBRD). Our results show that higher sand percentage was found during the intense glacial episodes, and their magnetic grain size analysis could help in distinguishing their provenance. We elaborate that particle size specific magnetic measurements of sand fractions could help in rapidly characterizing the glacial episodes in the subpolar North Atlantic.

East Asian monsoon precipitation decrease during Plio-Pleistocene transition revealed by changes in the chemical weathering intensity of Red Clay and loess-paleosol

East Asian Monsoon variations during the Plio-Pleistocene transition have attracted much scientific interest, but they are still not well understood. We analysed the trace and major element concentrations of the Red Clay and loess-paleosol sequence of the XSC section, on the southern Chinese Loess Plateau (CLP), over the time interval of 4–2 Ma. From the results of geochemical and mineralogical analysis, we conclude that the Na/K ratio can be used to reflect the weathering intensity of plagioclase. Grain- size effects on the Na/K ratio were minimized based on the analysis of multiple size fractions. The Na/K ratios show similar trends between different grain-size fractions during the Pliocene-Pleistocene transition. Additionally, the Na/K ratio for various Holocene eolian sediments is well correlated with the regional mean annual precipitation (MAP). Based on this observation, we relate the Na/K ratio to East Asian Summer Monsoon (EASM) precipitation and propose that the EASM is the primary control of the post-depositional weathering intensity. The Na/K record of the EASM precipitation, as inferred from the Na/K record of the XSC section, progressively weakened and increased in amplitude between 4 and 2 Ma, indicating that the climate on the monsoonal margin evolved from warm and moist during the Late Pliocene to dry and cold during the Early Pleistocene. Our results support the hypothesis that global cooling was responsible for driving the decrease in EASM-derived rainfall via the migration of the intertropical convergence zone (ITCZ) and the associated monsoon precipitation belt during the Plio-Pleistocene transition.

The Río Grío–Pancrudo Fault Zone (central Iberian Chain, Spain): recent extensional activity revealed by drainage reversal

AbstractThe NNW–SSE-trending extensional Río Grío–Pancrudo Fault Zone is a large-scale structure that obliquely cuts the Neogene NW–SE Calatayud Basin. Its negative inversion during the Neogene–Quaternary extension gave rise to structural and geomorphological rearrangement of the basin margin. Geological mapping has allowed two right-relayed fault segments to be distinguished, whose recent extensional activity has been mainly characterized using a deformed planation surface (Fundamental Erosion Surface (FES) 3; 3.5 Ma) as a geomorphic marker. Normal slip along the Río Grío–Lanzuela Fault Segment has induced hanging-wall tilting, subsequent drainage reversal at the Güeimil valley after the Pliocene–Pleistocene transition, as well as morphological scarps and surficial ruptures in Pleistocene materials. In this sector, an offset of FES3 indicates a total throw of c. 240 m, resulting in a slip rate of 0.07 mm a–1, while retrodeformation of hanging-wall tilting affecting a younger piedmont surface allows the calculation of a minimum throw in the range of 140–220 m after the Pliocene–Pleistocene transition, with a minimum slip rate of 0.07–0.11 mm a–1. For the late Pleistocene period, vertical displacement of c. 20 m of a sedimentary level dated to 66.6 ± 6.5 ka yields a slip rate approaching 0.30–0.36 mm a–1. At the Cucalón–Pancrudo Fault Segment, the offset of FES3 allows the calculation of a maximum vertical slip of 300 m for the last 3.5 Ma, and hence a net slip rate close to 0.09 mm a–1. Totalling c. 88 km in length, the Río Grío–Pancrudo Fault Zone could be the largest recent macrostructure in the Iberian Chain, probably active, with the corresponding undeniable seismogenic potential.

Early Pleistocene climate-induced erosion of the Alaska Range formed the Nenana Gravel

Abstract The Pliocene-Pleistocene transition resulted in extensive global cooling and glaciation, but isolating this climate signal within erosion and exhumation responses in tectonically active regimes can be difficult. The Nenana Gravel is a foreland basin deposit in the northern foothills of the Alaska Range (USA) that has long been linked to unroofing of the Alaska Range starting ca. 6 Ma. Using 26Al/10Be cosmogenic nuclide burial dating, we determined the timing of deposition of the Nenana Gravel and an overlying remnant of the first glacial advance into the northern foothills. Our results indicate that initial deposition of the Nenana Gravel occurred at the onset of the Pleistocene ca. 2.34 Ma and continued until at least ca. 1.7 Ma. The timing of initial deposition is correlative with expansion of the Cordilleran ice sheet, suggesting that the deposit formed due to increased glacial erosion in the Alaska Range. Abandonment of Nenana Gravel deposition occurred prior to the first glaciation extending into the northern foothills. This glaciation was hypothesized to have occurred ca. 1.5 Ma, but we found that it occurred ca. 0.39 Ma. A Pleistocene age for the Nenana Gravel and marine oxygen isotope stage 10 age for the oldest glaciation of the foothills necessitate reanalysis of incision and tectonic rates in the northern foothills of the Alaska Range, in addition to a shift in perspective on how these deposits fit into the climatic and tectonic history of the region.

A Pliocene\u2013Pleistocene continental biota from Venezuela

The Pliocene–Pleistocene transition in the Neotropics is poorly understood despite the major climatic changes that occurred at the onset of the Quaternary. The San Gregorio Formation, the younger unit of the Urumaco Sequence, preserves a fauna that documents this critical transition. We report stingrays, freshwater bony fishes, amphibians, crocodiles, lizards, snakes, aquatic and terrestrial turtles, and mammals. A total of 49 taxa are reported from the Vergel Member (late Pliocene) and nine taxa from the Cocuiza Member (Early Pleistocene), with 28 and 18 taxa reported for the first time in the Urumaco sequence and Venezuela, respectively. Our findings include the first fossil record of the freshwater fishes Megaleporinus, Schizodon, Amblydoras, Scorpiodoras, and the pipesnake Anilius scytale, all from Pliocene strata. The late Pliocene and Early Pleistocene ages proposed here for the Vergel and Cocuiza members, respectively, are supported by their stratigraphic position, palynology, nannoplankton, and 86Sr/88Sr dating. Mammals from the Vergel Member are associated with the first major pulse of the Great American Biotic Interchange. In contrast to the dry conditions prevailing today, the San Gregorio Formation documents mixed open grassland/forest areas surrounding permanent freshwater systems, following the isolation of the northern South American basin from western Amazonia. These findings support the hypothesis that range contraction of many taxa to their current distribution in northern South America occurred rapidly during at least the last 1.5 million years.

Basin inversion: A worldwide Late Cenozoic phenomenon

Abstract The occurrence of endorheic basins on the Tibetan Plateau, both in its Pleistocene history and (fewer in number) at the present day, has been attributed to the ‘basin-and-range’ character of the orogen; the understanding of their conversion to exorheic drainage is key to interpreting the evolution of the Yellow River and other river systems of the plateau. However, such basins also occur in areas of lower altitude and relief and can be observed to have been considerably more common in pre-Quaternary times. In many areas, for example the Mediterranean region, such basins, previously having accumulated stacked sedimentary sequences, typically ‘inverted’ in the late Pliocene or at around the Pliocene–Pleistocene transition, possibly as part of a response to the cooling of global climate and its effect on surface processes. Some basins have inverted later, at around the time of the Mid-Pleistocene Revolution, coinciding with the increased severity of climate resulting from the 100 ka Milankovich cycles that followed that change. The progressive incision into the fills of these inverted sedimentary basins has also been linked to this climatic influence, perhaps taking effect as a result of erosional isostatic uplift, which would have replaced the accumulation-induced subsidence (also isostatic) of the basins. NW Europe, including Britain, had sediment-accumulating basins in the Early Cenozoic; the timing of their inversion is poorly known as a result of the paucity of preserved evidence from the Late Cenozoic in such areas. Endorheic basins that survive at the present day are mainly in regions of relative aridity and are often controlled by active tectonic structures, such as the pull-apart basins of the Dead Sea Fault Zone and similar examples. This review discusses the evidence from different climatic regions, tectonic settings and areas of different crustal type, with a view to elucidating meaningful patterns that might throw light on this phenomenon.

Topological Climate Change

This article presents a bifurcation analysis of a simple Energy Balance Model (EBM) of the Earth’s climate, which suggests that topological change has occurred in the paleoclimate history of the Earth. In the theory of dynamical systems, two systems that are topologically equivalent have solutions with the same qualitative behavior. A change in the topological equivalence class, as parameters are varied, is called a bifurcation. Thus, a bifurcation demarcates a significant change in the behavior of the solutions of a dynamical system. If that system represents climate, then that topological change may represent an abrupt transformation of the climate, occurring even with a very small change in the forcing parameters. In this paper, the existence of a cusp bifurcation is proven in a climate EBM. The existence of this cusp bifurcation implies the co-existence of two distinct stable equilibrium climate states (bistability), as well as the existence of abrupt transitions between these two states (fold bifurcations) in the EBM. These transitions are dependent on the past history of the system (hysteresis). The two universal unfolding parameters for the cusp bifurcation have been determined as functions of the relevant physical parameters. These ideas lead to the proposal of a new explanation for the so-called warm equable climate problem of the mid-Cretaceous and early Eocene. The analysis presented here implies that the mid-Cretaceous and early Eocene climate systems are topologically equivalent to each other, but they are not topologically equivalent to the preindustrial modern climate. The transition from the warm, equable paleoclimate to today’s cooler nonequable climate occurs via fold (or saddle-node) bifurcations in the EBM, which correspond to the Eocene-Oligocene Transition (EOT) at the south pole and the Pliocene-Pleistocene Transition (PPT) at the north pole, in the paleoclimate record of Earth.

On the origin and diversification history of the African genus Encephalartos

Of the 10 known genera of cycads, the genus Encephalartos is one of the two endemic genera to Africa. Although a number of studies have explored the taxonomic relationships within the genus as well as its diversification history, we still have limited understanding of its historical biogeography. In the present study, using five gene markers, we first reconstructed a complete phylogeny of the genus and its historical biogeography based on S-DIVA model. We then fitted the COMET model to the phylogeny to test for significant shifts in evolutionary events that may have driven the current diversity in the genus. Overall, our phylogeny is well supported and reveals two major clades following species geographic origins, one southern African clade and one east-central-west African clade. Our biogeographic analysis suggests that the genus may have diverged around 9 Ma from southern Africa (100% probability) and then colonized the region through dispersal. Although the origin of the east-central-west African clade is uncertain (50% probability), the clade may have diverged from the southern African clade through vicariance. We suggest that the eastern rift system in eastern Africa and the west African Dahomey Gap – a dry corridor that breaks pan-African tropical rainforest into different blocks – are geographical barriers limiting dispersal into the rest of the continent whilst, at the same time, promoting the vicariance signature observed. Although most species accumulated in the last 2.6 My, there were no significant shifts in any of the evolutionary events, suggesting that an overall constant-rate diversification model is best suited for the genus and that the rapid species accumulation during the Pliocene–Pleistocene transition may not be as dramatic as initially thought.

Environmental signals of Pliocene-Pleistocene climatic changes in Central Europe: Insights from the mineral magnetic record of the Heidelberg Basin sedimentary infill (Germany)

Abstract The entrance of Earth's climate into the present icehouse state during a time of rapid temperature decline in the late Pliocene was intensively investigated during the past decade. Even though it is well documented in marine archives, a detailed reconstruction of the Pliocene-Pleistocene climatic evolution of Central Europe is hampered by a general lack of data. The work presented here is based on sedimentary material from drill cores obtained at three sites within the Heidelberg Basin (Germany). The scientific relevance of this unique archive was discovered only in the last decade. The hundreds of metres thick sequences of mainly fluvial sediments record the evolution of the environment and climatic conditions during the late Pliocene and the entire Pleistocene of western Central Europe. In our present study, we implement unpublished mineral magnetic S-ratio data, and new evidence from X-ray analysis into two previously completed studies on the magnetic polarity stratigraphy, and the magnetic mineralogy of the Pliocene to Pleistocene sediments of the Heidelberg Basin. The total set of data enables distinction of environmental and climatic processes, and unveil details on the climatic conditions of continental Europe during this period. We demonstrate the dominance of a warm climate with alternation of humid and dry periods during the Pliocene. Cyclic variations in the groundwater table in the Rhine flood plain resulted in redox fluctuations, which led to the decomposition of the primary detrital mineral assemblage. Authigenic Fe oxides, particularly haematite, formed during dry periods. A rapid transition into cooler and moister conditions occurred at the end of the Pliocene, as indicated by the persistence of Fe sulphides, especially greigite. A high groundwater table and the associated reducing conditions have largely persisted to the present day. We show that the rapid transition from warm to cooler and moister climatic conditions in Central Europe during the final Pliocene is a regional response to the intensification of Northern Hemisphere glaciation (iNHG). This work supplements existing knowledge of the climatic evolution of Central Europe during the Pliocene-Pleistocene transition by data from a region from which little data has been available. A sideglance to climatic archives elsewhere in the Northern Hemisphere (e.g., North Atlantic Ocean, Chinese Loess Plateau, Russian arctic) is used to show the coincidence of the iNHG events in quite different environmental regimes.

Chromosomal dynamics in space and time: evolutionary history of Mycetophylax ants across past climatic changes in the Brazilian Atlantic coast

Fungus-farming ants of the genus Mycetophylax exhibit intra and interspecific chromosome variability, which makes them suitable for testing hypotheses about possible chromosomal rearrangements that endure lineage diversification. We combined cytogenetic and molecular data from Mycetophylax populations from coastal environments to trace the evolutionary history of the clade in light of chromosomal changes under a historical and geographic context. Our cytogenetic analyses revealed chromosomal differences within and among species. M. morschi exhibited three distinct karyotypes and considerable variability in the localization of 45S rDNA clusters. The molecular phylogeny was congruent with our cytogenetic findings. Biogeographical and divergence time dating analyses estimated that the most recent common ancestor of Mycetophylax would have originated at about 30 Ma in an area including the Amazon and Southern Grasslands, and several dispersion and vicariance events may have occurred before the colonization of the Brazilian Atlantic coast. Diversification of the psammophilous Mycetophylax first took place in the Middle Miocene (ca. 18–10 Ma) in the South Atlantic coast, while “M. morschi” lineages diversified during the Pliocene-Pleistocene transition (ca. 3–2 Ma) through founder-event dispersal for the Northern coastal regions. Psammophilous Mycetophylax diversification fits into the major global climatic events that have had a direct impact on the changes in sea level as well as deep ecological impact throughout South America. We assume therefore that putative chromosomal rearrangements correlated with increased ecological stress during the past climatic transitions could have intensified and/or accompanied the divergence of the psammophilous Mycetophylax. We further reiterate that “M. morschi” comprises a complex of at least three well-defined lineages, and we emphasize the role of this integrative approach for the identification and delimitation of evolutionary lineages.

Pliocene and Early Pleistocene glaciation and landscape evolution on the Patagonian Steppe, Santa Cruz province, Argentina

At least seven late Pliocene tills cap plateaus (mesetas) south of Lago Viedma, just east of the Andes in Argentine Patagonia. Chronologic constraints on the tills are provided by 40Ar/39Ar ages and magnetic polarities on associated basalt flows and sediments. The tills were deposited by piedmont glaciers that reached at least 80 km east of the crest of the Andes and flowed on a low-relief surface sloping gently downward in that direction. The oldest of the tills is about 3.6 Ma old. Glacial deposits dating to the Pliocene-Pleistocene transition are present at least 40 km beyond the east limit of the Pliocene tills at Lago Viedma, and tills of similar age occur at Condor Cliff in the Río Santa Cruz valley to the southeast. A sequence of at least seven Early Pleistocene (2.1–1.1 Ma) tills is present between basalt flows in the Cerro del Fraile meseta south of Lago Argentino. The glaciers that deposited these Early Pleistocene tills reached far beyond the Marine Isotope Stage 2 limit in the Río Santa Cruz valley. Based on positions, extents, and ages of the un-deformed, basalt-capped mesetas flanking Lago Viedma, we conclude that the topography in this area was profoundly changed during the Pleistocene – the low to moderate relief Pliocene surface was deeply incised by glaciers that became increasingly confined to, and flowed within, troughs. The valley floors today are up to 1350 m below the late Pliocene surface.

Late Pliocene and early Pleistocene vegetation and climate change revealed by a pollen record from Nihewan Basin, North China

The Nihewan Formation is an important early Quaternary sedimentary formation in North China. We conducted pollen analyses of 183 samples and 1611 modern surface samples to characterize the processes of vegetation succession and climate change during the Pliocene-Pleistocene transition (2.89–2.34 Ma) in the Nihewan Basin. The results show that pollen assemblages are dominated by arboreal pollen, indicating that the vegetation in the study area was forest dominated and that the climate was more humid than today, however, the temperature varied substantially. The most substantial vegetation and climate changes occurred at ∼2.8 Ma, when the pollen representation of warm and humid tolerant taxa such as evergreen Quercus and Carya disappeared, and also broadleaved deciduous types such as Ulmus, deciduous Quercus and Betula decreased obviously, on the contrary, the pollen representation of cold and drought tolerant taxa increased substantially: e.g. Picea (from generally less than 20% to more than 30%) and Chenopodiaceae (from generally less than 10% to more than 20%). The quantitative reconstructed results indicating that Tann decreased by about 2–3 °C and Pann decreased by ∼150 mm compared to before 2.8 Ma, with a maximum decrease of ∼9 °C for Tann and ∼450 mm for Pann. Another important vegetation and climate changes occurred at ∼2.6 Ma, which was the coldest and driest of the studied interval, when the vegetation was substantially simplified with spruce (generally above 80%) as the dominated types.

New fossils of Eucladoceros boulei (Artiodactyla, Mammalia) from Early Pleistocene Nihewan Beds, China

Recent excavations at Shanshenmiaozui site in Nihewan Basin of North China uncovered a rich collection of comb-antlered deer, which includes the first discovery of the yearling antler, complete upper and lower dentitions (both deciduous and permanent), associated limb bones including the longest metapodials ever recovered. Based on toothrow length and the dental characters as well as the postcranial bones, the new fossil materials can be referred to Eucladoceros boulei that is estimated to be 350kg and represents the largest Pleistocene cervid ever recovered in China. Besides the large size, E. boulei is also characterized by the pronounced anterior cingulids and entostylid ribs on lower molars as well as the moderately pachyostosed mandibles. The present study shows that the body weight of large cervids can be estimated by the length of toothrow and metacarpal, with exception for Cervus elaphus, which has larger toothrow length, but shorter metacarpal and smaller body size. E. boulei is a typical element of the Early Pleistocene fauna in northern China. The early Villafranchian is a bottleneck period for cervid evolution in northern China, which is characterized by the following features: decrease of cervid diversity, disappearance of archaic groups, and the rise of the medium to large-sized three-tined cervini taxa. The sudden appearance of the very large and/or multi-tined cervids at the Pliocene–Pleistocene transition may represent a great migration event of mammals. The Early Pleistocene cervids from Nihewan Basin are very diverse, and are in need of more taxonomic work.

Chronostratigraphic distribution of cetaceans in the Pliocene of Northern Apennines (Italy): palaeoecological implications

A large number of cetacean fossils have been recovered through the time from the Pliocene deposits in Northern Apennines thrust belt, on both the Padan-Adriatic and the Tyrrhenian side. In this work, the cetaceans of Castell'Arquato Basin (Padan-Adriatic side) have been placed within a high-resolution chronostratigraphic framework available for this area. This results in a better assessment of their evolutionary history and of the palaeoecologic factors controlling their diversity and abundance through the time.Our results document a greater diversity between 3.1 and 2.7 Ma time interval, likely due to the development of eutrophic conditions during precessionally-driven insolation maxima at 400 ka eccentricity maxima, which are recorded in deeper depositional settings by sapropel clusters. Eutrophic conditions kept a complex trophic chain, as currently observed in the Ligurian Sea (Corsican-Ligurian-Provençal Basin), an area characterized also by upwelling. A reduction in both number and ecological diversity of cetacean taxa is observed along the Pliocene-Pleistocene transition; this trend, related to the onset of the Quaternary icehouse conditions, appears in good agreement with the recently recognized extinction event that affecting the marine megafauna at the end of the Pliocene.