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"Eocene"
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Rhinoceros giants : the paleobiology of Indricotheres
Introduces the giant hornless rhinoceros, Indricotherium. These massive animals inhabited Asia and Eurasia for more than 14 million years, about 23 to 37 million years ago. They had skulls 6 feet long, stood 22 feet high at the shoulder, and were twice as heavy as the largest elephant ever recorded, tipping the scales at 44,100 pounds. Fortunately, the big brutes were vegetarians.
Book
Correction: Eocene metatherians from Anatolia illuminate the assembly of an island fauna during Deep Time
[This corrects the article DOI: 10.1371/journal.pone.0206181.].
Journal Article
Assessing the Duration of the Paleocene‐Eocene Thermal Maximum
The Paleocene‐Eocene Thermal Maximum (PETM) was a climate/carbon cycle perturbation recognized in stable carbon isotope (δ13C) records with a negative carbon isotope excursion (CIE). The PETM CIE termination has been associated with a δ13C inflection with pre‐PETM‐like values referred to as the G point. However, the G point approach has produced variable PETM CIE duration estimates (∼120–230 kyr), which reflects a need to test its reliability. Here, we apply statistical analyses to existing δ13C records and reveal that the G point is sensitive to underlying δ13C uncertainties. We generate a probabilistic‐based CIE detection limit, which constrains the time range over which the PETM is detected in δ13C records. This protocol reveals a protracted CIE recovery (>145 kyr) that accounts for a 268.8+21.2/−20.5 kyr PETM CIE duration. Our new duration estimate exceeds previous values, which confirms the potential of extreme carbon cycle perturbations to cause long‐lasting carbon cycle disruptions.
Journal Article
Correction: Skeleton of an unusual, cat-sized marsupial relative (Metatheria: Marsupialiformes) from the middle Eocene (Lutetian: 44-43 million years ago) of Turkey
Citation: Maga AM, Beck RMD (2017) Correction: Skeleton of an unusual, cat-sized marsupial relative (Metatheria: Marsupialiformes) from the middle Eocene (Lutetian: 44-43 million years ago) of Turkey.
Maga AM, Beck RMD (2017) Skeleton of an unusual, cat-sized marsupial relative (Metatheria: Marsupialiformes) from the middle Eocene (Lutetian: 44–43 million years ago) of Turkey.
Journal Article
Sedimentology and chronostratigraphy of the Apt Basin, southeastern France; lacustrine response to Late Paleogene cooling and regional rifting
The Apt Basin, sub-basin of the wider Manosque Basin of southeastern France, contains deposits of Eocene-Oligocene lake systems that were part of a broader network of evaporative lakes and lagoons spread across the European Cenozoic rift system. The onset and mechanisms of subsidence in the rift system, the interconnectivity of these lakes, and their response to the transition into the Oligocene icehouse are poorly understood. This study aims to clarify these points by examining the stratigraphy and depositional environments in the Apt Basin. We correlate and date Eocene to lowermost Oligocene geological units using a basin-wide facies model combined with sedimentological and geochronological approaches. We show the existence of three lacustrine phases, each separated by complete lake drying events: (1) an Ypresian (?) - Lutetian lake-marsh system dominated by palustrine carbonates; (2) a Bartonian (?) - Priabonian siliciclastic fluvio-deltaic and saline lake system; and (3) a lower Rupelian saline carbonate lake system. The presence of a lake system during the Ypresian (?) - Lutetian suggests an onset of basin subsidence before most other basins of the rift system in southeastern France, and is associated with the late Pyrenean deformation phase. The initiation of the second lacustrine phase marks the beginning of E-W extension and the formation of the Apt Basin as an individual horst & graben system. Based on facies distribution, we demonstrate the hydrological isolation of the Apt Basin from other basins and the improbability of any marine connection during the first two phases. This isolation is less certain for the third phase. We show a close synchronicity between the second lake drying event and the Eocene-Oligocene Transition. The third lacustrine phase, dominated by carbonate production and low siliciclastic input, is interpreted as reflecting a long-term decrease in surface runoff associated with the fall into the Oligocene icehouse.
Journal Article
The enigma of Oligocene climate and global surface temperature evolution
Falling atmospheric CO₂ levels led to cooling through the Eocene and the expansion of Antarctic ice sheets close to their modern size near the beginning of the Oligocene, a period of poorly documented climate. Here, we present a record of climate evolution across the entire Oligocene (33.9 to 23.0 Ma) based on TEX86 sea surface temperature (SST) estimates from southwestern Atlantic Deep Sea Drilling Project Site 516 (paleolatitude ∼36°S) and western equatorial Atlantic Ocean Drilling Project Site 929 (paleolatitude ∼0°), combined with a compilation of existing SST records and climate modeling. In this relatively low CO₂ Oligoceneworld (∼300 to 700 ppm),warm climates similar to those of the late Eocene continued with only brief interruptions, while the Antarctic ice sheet waxed and waned. SSTs are spatially heterogenous, but generally support late Oligocene warming coincident with declining atmospheric CO₂. This Oligocene warmth, especially at high latitudes, belies a simple relationship between climate and atmospheric CO₂ and/or ocean gateways, and is only partially explained by current climate models. Although the dominant climate drivers of this enigmatic Oligocene world remain unclear, our results help fill a gap in understanding past Cenozoic climates and the way long-term climate sensitivity responded to varying background climate states.
Journal Article
Spatial patterns of climate change across the Paleocene—Eocene Thermal Maximum
The Paleocene—Eocene Thermal Maximum (PETM; 56 Ma) is one of our best geological analogs for understanding climate dynamics in a “greenhouse” world. However, proxy data representing the event are only available from select marine and terrestrial sedimentary sequences that are unevenly distributed across Earth’s surface, limiting our view of the spatial patterns of climate change. Here, we use paleoclimate data assimilation (DA) to combine climate model and proxy information and create a spatially complete reconstruction of the PETM and the climate state that precedes it (“PETM-DA”). Our data-constrained results support strong polar amplification, which in the absence of an extensive cryosphere, is related to temperature feedbacks and loss of seasonal snow on land. The response of the hydrological cycle to PETM warming consists of a narrowing of the Intertropical Convergence Zone, off-equatorial drying, and an intensification of seasonal monsoons and winter storm tracks. Many of these features are also seen in simulations of future climate change under increasing anthropogenic emissions. Since the PETM-DA yields a spatially complete estimate of surface air temperature, it yields a rigorous estimate of global mean temperature change (5.6 ◦C; 5.4 ◦C to 5.9 ◦C, 95% CI) that can be used to calculate equilibrium climate sensitivity (ECS). We find that PETM ECS was 6.5 ◦C (5.7 ◦C to 7.4 ◦C, 95% CI), which is much higher than the present-day range. This supports the view that climate sensitivity increases substantially when greenhouse gas concentrations are high.
Journal Article
Silicate and Carbonate Weathering Perturbation at the Eocene‐Oligocene Transition Recorded by Mg Isotopes
During the Eocene‐Oligocene Transition (ca. 34 Ma), the Earth underwent a dramatic decline in atmospheric CO2, global cooling, a deepening of the carbonate compensation depth (CCD), and the formation of a permanent ice sheet on Antarctica. The expansion of Antarctic glaciers eroded the underlying bedrock and increased the weathering flux to the ocean. However, the role silicate and carbonate weathering play in atmospheric CO2 removal and the CCD through Ca2+ and alkalinity production is poorly understood. Magnesium isotopes (δ26Mg) are fractionated during carbonate and clay mineral formation and can be used to quantify the relative flux from silicate and carbonate weathering. Here, we report the δ26Mg composition of the carbonate, reactive (ferromanganese coatings), and residual (silicate) fraction of marine sediments from the Kerguelen Plateau (Ocean Drilling Program Site 738), near a major drainage system of the East Antarctic Ice Sheet, to explore the response of subglacial and shelf weathering to ice sheet expansion. The δ26Mg of the carbonate fraction (−2.29‰ to −0.95‰), reactive fraction (−0.36‰ to 0.10‰), and residual fraction (−0.05‰ to 0.55‰) display similar values to surface‐dwelling calcareous nannofossils, deep‐water ferromanganese nodules, and Antarctic bedrock, respectively. Isotope fluctuations in all three phases suggest that the formation of the Antarctic ice sheet drove efficient chemical weathering of underlying silicate bedrock, which was rapidly transported to the Southern Ocean, resulting in further CO2 drawdown, while a local sea‐level low stand exposed carbonates on the Antarctic continental shelf to weathering, contributing to a deepening of the CCD.
Journal Article
Analysis of Phylogenomic Tree Space Resolves Relationships Among Marsupial Families
A fundamental challenge in resolving evolutionary relationships across the tree of life is to account for heterogeneity in the evolutionary signal across loci. Studies of marsupial mammals have demonstrated that this heterogeneity can be substantial, leaving considerable uncertainty in the evolutionary timescale and relationships within the group. Using simulations and a new phylogenomic data set comprising nucleotide sequences of 1550 loci from 18 of the 22 extant marsupial families, we demonstrate the power of a method for identifying clusters of loci that support different phylogenetic trees. We find two distinct clusters of loci, each providing an estimate of the species tree that matches previously proposed resolutions of the marsupial phylogeny. We also identify a well-supported placement for the enigmatic marsupial moles (Notoryctes) that contradicts previous molecular estimates but is consistent with morphological evidence. The pattern of gene-tree variation across tree-space is characterized by changes in information content, GC content, substitution-model adequacy, and signatures of purifying selection in the data. In a simulation study, we show that incomplete lineage sorting can explain the division of loci into the two tree-topology clusters, as found in our phylogenomic analysis of marsupials. We also demonstrate the potential benefits of minimizing uncertainty from phylogenetic conflict for molecular dating. Our analyses reveal that Australasian marsupials appeared in the early Paleocene, whereas the diversification of present-day families occurred primarily during the late Eocene and early Oligocene. Our methods provide an intuitive framework for improving the accuracy and precision of phylogenetic inference and molecular dating using genome-scale data.
Journal Article
Synchronous tropical and polar temperature evolution in the Eocene
Palaeoclimate reconstructions of periods with warm climates and high atmospheric CO
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concentrations are crucial for developing better projections of future climate change. Deep-ocean
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,
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and high-latitude
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palaeotemperature proxies demonstrate that the Eocene epoch (56 to 34 million years ago) encompasses the warmest interval of the past 66 million years, followed by cooling towards the eventual establishment of ice caps on Antarctica. Eocene polar warmth is well established, so the main obstacle in quantifying the evolution of key climate parameters, such as global average temperature change and its polar amplification, is the lack of continuous high-quality tropical temperature reconstructions. Here we present a continuous Eocene equatorial sea surface temperature record, based on biomarker palaeothermometry applied on Atlantic Ocean sediments. We combine this record with the sparse existing data
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,
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–
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to construct a 26-million-year multi-proxy, multi-site stack of Eocene tropical climate evolution. We find that tropical and deep-ocean temperatures changed in parallel, under the influence of both long-term climate trends and short-lived events. This is consistent with the hypothesis that greenhouse gas forcing
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,
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, rather than changes in ocean circulation
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,
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, was the main driver of Eocene climate. Moreover, we observe a strong linear relationship between tropical and deep-ocean temperatures, which implies a constant polar amplification factor throughout the generally ice-free Eocene. Quantitative comparison with fully coupled climate model simulations indicates that global average temperatures were about 29, 26, 23 and 19 degrees Celsius in the early, early middle, late middle and late Eocene, respectively, compared to the preindustrial temperature of 14.4 degrees Celsius. Finally, combining proxy- and model-based temperature estimates with available CO
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reconstructions
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yields estimates of an Eocene Earth system sensitivity of 0.9 to 2.3 kelvin per watt per square metre at 68 per cent probability, consistent with the high end of previous estimates
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A 26-million-year record of equatorial sea surface temperatures reveals synchronous changes of tropical and polar temperatures during the Eocene epoch forced by variations in concentrations of atmospheric carbon dioxide, with a constant degree of polar amplification.
Journal Article